https://github.com/grobian/carbon-c-relay

Enhanced C implementation of Carbon relay, aggregator and rewriter
https://github.com/grobian/carbon-c-relay

c graphite monitoring relays

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Enhanced C implementation of Carbon relay, aggregator and rewriter

• Host: GitHub
• URL: https://github.com/grobian/carbon-c-relay
• Owner: grobian
• License: apache-2.0
• Created: 2013-12-21T10:33:29.000Z (about 11 years ago)
• Default Branch: master
• Last Pushed: 2024-09-28T13:13:00.000Z (4 months ago)
• Last Synced: 2025-01-12T06:02:52.022Z (10 days ago)
• Topics: c, graphite, monitoring, relays
• Language: C
• Homepage:
• Size: 4.08 MB
• Stars: 379
• Watchers: 40
• Forks: 107
• Open Issues: 20
• Metadata Files:
  • Readme: README.md
  • Changelog: ChangeLog.md
  • License: LICENSE.md

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README

        
carbon-c-relay(1) -- graphite relay, aggregator and rewriter

============================================================

[![Build Status](https://github.com/grobian/carbon-c-relay/actions/workflows/build-test-ci.yml/badge.svg)](https://github.com/grobian/carbon-c-relay/actions/workflows/build-test-ci.yml)

## SYNOPSIS

`carbon-c-relay` `-f` *config-file* `[ options` ... `]`

## DESCRIPTION

**carbon-c-relay** accepts, cleanses, matches, rewrites, forwards and

aggregates graphite metrics by listening for incoming connections and

relaying the messages to other servers defined in its configuration.

The core functionality is to route messages via flexible rules to the

desired destinations.

**carbon-c-relay** is a simple program that reads its routing information

from a file.  The command line arguments allow to set the location for

this file, as well as the amount of dispatchers (worker threads) to use

for reading the data from incoming connections and passing them onto the

right destination(s).  The route file supports two main constructs:

clusters and matches.  The first define groups of hosts data metrics can

be sent to, the latter define which metrics should be sent to which

cluster.  Aggregation rules are seen as matches.  Rewrites are actions

that directly affect the metric at the point in which they appear in the

configuration.

For every metric received by the relay, cleansing is performed.  The

following changes are performed before any match, aggregate or rewrite

rule sees the metric:

  - double dot elimination (necessary for correctly functioning

    consistent hash routing)

  - trailing/leading dot elimination

  - whitespace normalisation (this mostly affects output of the relay

    to other targets: metric, value and timestamp will be separated by

    a single space only, ever)

  - irregular char replacement with underscores (\_), currently

    irregular is defined as not being in `[0-9a-zA-Z-_:#]`, but can be

    overridden on the command line.

    Note that tags (when present and allowed) are not processed this

    way.

## OPTIONS

These options control the behaviour of **carbon-c-relay**.

  * `-v`:

    Print version string and exit.

  * `-d`:

    Enable debug mode, this prints statistics to stdout and prints extra

    messages about some situations encountered by the relay that normally

    would be too verbose to be enabled.  When combined with `-t`

    (test mode) this also prints stub routes and consistent-hash ring

    contents.

  * `-s`:

    Enable submission mode.  In this mode, internal statistics are not

    generated.  Instead, queue pressure and metrics drops are reported on

    stdout.  This mode is useful when used as submission relay which'

    job is just to forward to (a set of) main relays.  Statistics about

    the submission relays in this case are not needed, and could easily

    cause a non-desired flood of metrics e.g. when used on each and

    every host locally.

  * `-S`:

    Enable iostat-like mode where every second the current state of

    statistics are reported.  This implies submission mode `-s`.

  * `-t`:

    Test mode.  This mode doesn't do any routing at all, but instead reads

    input from stdin and prints what actions would be taken given the loaded

    configuration.  This mode is very useful for testing relay routes for

    regular expression syntax etc.  It also allows to give insight on how

    routing is applied in complex configurations, for it shows rewrites and

    aggregates taking place as well.  When `-t` is repeated, the relay

    will only test the configuration for validity and exit immediately

    afterwards.  Any standard output is suppressed in this mode, making

    it ideal for start-scripts to test a (new) configuration.

  * `-f` *config-file*:

    Read configuration from *config-file*.  A configuration consists of

    clusters and routes.  See [CONFIGURATION SYNTAX](#configuration-syntax)

    for more information on the options and syntax of this file.

  * `-l` *log-file*:

    Use *log-file* for writing messages.  Without this option, the relay

    writes both to *stdout* and *stderr*.  When logging to file, all

    messages are prefixed with `MSG` when they were sent to *stdout*, and

    `ERR` when they were sent to *stderr*.

  * `-p` *port*:

    Listen for connections on port *port*.  The port number is used for

    both `TCP`, `UDP` and `UNIX sockets`.  In the latter case, the socket

    file contains the port number.  The port defaults to *2003*, which is

    also used by the original `carbon-cache.py`.  Note that this only

    applies to the defaults, when `listen` directives are in the config,

    this setting is ignored.

  * `-w` *workers*:

    Use *workers* number of threads.  The default number of workers is

    equal to the amount of detected CPU cores.  It makes sense to reduce

    this number on many-core machines, or when the traffic is low.

  * `-b` *batchsize*:

    Set the amount of metrics that sent to remote servers at once to

    *batchsize*.  When the relay sends metrics to servers, it will

    retrieve `batchsize` metrics from the pending queue of metrics waiting

    for that server and send those one by one.  The size of the batch will

    have minimal impact on sending performance, but it controls the amount

    of lock-contention on the queue.  The default is *2500*.

  * `-q` *queuesize*:

    Each server from the configuration where the relay will send metrics

    to, has a queue associated with it.  This queue allows for disruptions

    and bursts to be handled.  The size of this queue will be set to

    *queuesize* which allows for that amount of metrics to be stored in

    the queue before it overflows, and the relay starts dropping metrics.

    The larger the queue, more metrics can be absorbed, but also more

    memory will be used by the relay.  The default queue size is *25000*.

  * `-L` *stalls*:

    Sets the max mount of stalls to *stalls* before the relay starts

    dropping metrics for a server.  When a queue fills up, the relay uses

    a mechanism called stalling to signal the client (writing to the

    relay) of this event.  In particular when the client sends a large

    amount of metrics in very short time (burst), stalling can help to

    avoid dropping metrics, since the client just needs to slow down for a

    bit, which in many cases is possible (e.g. when catting a file with

    `nc`(1)).  However, this behaviour can also obstruct, artificially

    stalling writers which cannot stop that easily.  For this the stalls

    can be set from *0* to *15*, where each stall can take around 1 second

    on the client.  The default value is set to *4*, which is aimed at the

    occasional disruption scenario and max effort to not loose metrics

    with moderate slowing down of clients.

  * `-C` *CAcertpath*:

    Read CA certs (for use with TLS/SSL connections) from given path or

    file.  When not given, the default locations are used.  Strict

    verfication of the peer is performed, so when using self-signed

    certificates, be sure to include the CA cert in the default

    location, or provide the path to the cert using this option.

  * `-T` *timeout*:

    Specifies the IO timeout in milliseconds used for server connections.

    The default is *600* milliseconds, but may need increasing when WAN

    links are used for target servers.  A relatively low value for

    connection timeout allows the relay to quickly establish a server is

    unreachable, and as such failover strategies to kick in before the

    queue runs high.

  * `-c` *chars*:

    Defines the characters that are next to `[A-Za-z0-9]` allowed in

    metrics to *chars*.  Any character not in this list, is replaced by

    the relay with `_` (underscore).  The default list of allowed

    characters is *-_:#*.

  * `-m` *length*:

    Limits the metric names to be of at most *length* bytes long.  Any

    lines containing metric names larger than this will be discarded.

  * `-M` *length*

    Limits the input to lines of at most *length* bytes.  Any excess

    lines will be discarded.  Note that `-m` needs to be smaller than

    this value.

  * `-H` *hostname*:

    Override hostname determined by a call to `gethostname`(3) with

    *hostname*.  The hostname is used mainly in the statistics metrics

    `carbon.relays..<...>` sent by the relay.

  * `-B` *backlog*:

    Sets TCP connection listen backlog to *backlog* connections.  The

    default value is *32* but on servers which receive many concurrent

    connections, this setting likely needs to be increased to avoid

    connection refused errors on the clients.

  * `-U` *bufsize*:

    Sets the socket send/receive buffer sizes in bytes, for both TCP and UDP

    scenarios.  When unset, the OS default is used.  The maximum is also

    determined by the OS.  The sizes are set using setsockopt with the flags

    SO_RCVBUF and SO_SNDBUF.  Setting this size may be necessary for large

    volume scenarios, for which also `-B` might apply.  Checking the *Recv-Q*

    and the *receive errors* values from *netstat* gives a good hint

    about buffer usage.

  * `-E`:

    Disable disconnecting idle incoming connections.  By default the

    relay disconnects idle client connections after 10 minutes.  It does

    this to prevent resources clogging up when a faulty or malicious

    client keeps on opening connections without closing them.  It

    typically prevents running out of file descriptors.  For some

    scenarios, however, it is not desirable for idle connections to be

    disconnected, hence passing this flag will disable this behaviour.

  * `-D`:

    Deamonise into the background after startup.  This option requires

    `-l` and `-P` flags to be set as well.

  * `-P` *pidfile*:

    Write the pid of the relay process to a file called *pidfile*.  This

    is in particular useful when daemonised in combination with init

    managers.

  * `-O` *threshold*:

    The minimum number of rules to find before trying to optimise the

    ruleset.  The default is `50`, to disable the optimiser, use `-1`,

    to always run the optimiser use `0`.  The optimiser tries to group

    rules to avoid spending excessive time on matching expressions.

## CONFIGURATION SYNTAX

The config file supports the following syntax, where comments start with

a `#` character and can appear at any position on a line and suppress

input until the end of that line:

```

cluster 

    <  [useall] |

       [replication ] [dynamic] >

        ]

                                [type linemode]

                                [transport 

                                           [ssl | mtls  ]]> ...

    ;

cluster 

    file [ip]

         ...

    ;

match

        <* | expression ...>

    [validate  else ]

    send to 

    [stop]

    ;

rewrite 

    into 

    ;

aggregate

         ...

    every  seconds

    expire after  seconds

    [timestamp at  of bucket]

    compute  | variance | stddev> write to

        

    [compute ...]

    [send to ]

    [stop]

    ;

send statistics to 

    [stop]

    ;

statistics

    [submit every  seconds]

    [reset counters after interval]

    [prefix with ]

    [send to ]

    [stop]

    ;

listen

    type linemode [transport 

                      [ 

                          [protomin ] [protomax ]

                          [ciphers ] [ciphersuites ]

                      ]

                  ]

        < proto > ...

         ...

    ;

    # tlsproto: 

    # ssl-ciphers: see ciphers(1)

    # tls-suite: see SSL_CTX_set_ciphersuites(3)

include 

    ;

```

### CLUSTERS

Multiple clusters can be defined, and need not to be referenced by a

match rule.   All clusters point to one or more hosts, except the `file`

cluster which writes to files in the local filesystem.  `host` may be an

IPv4 or IPv6 address, or a hostname.  Since host is followed by an

optional `:` and port, for IPv6 addresses not to be interpreted wrongly,

either a port must be given, or the IPv6 address surrounded by brackets,

e.g. `[::1]`.  Optional `transport` and `proto` clauses can be used to

wrap the connection in a compression or encryption layer or specify the

use of UDP or TCP to connect to the remote server.  When omitted the

connection defaults to a plain TCP connection.  `type` can only be

`linemode` at the moment, e.g. Python's pickle mode is not supported.

DNS hostnames are resolved to a single address, according to the preference

rules in [RFC 3484](https://www.ietf.org/rfc/rfc3484.txt).  The

`any_of`, `failover` and `forward` clusters have an explicit `useall`

flag that enables expansion for hostnames resolving to multiple

addresses.  Using this option, each address of any type becomes a

cluster destination.  This means for instance that both IPv4 and IPv6

addresses are added.

There are two groups of cluster types, simple forwarding clusters and

consistent hashing clusters.

* `forward` and `file` clusters

  The `forward` and `file` clusters simply send everything they receive

  to the defined members (host addresses or files).  When a cluster has

  multiple members, all incoming metrics are sent to *all* members,

  basically duplicating the input metric stream over all members.

* `any_of` cluster

  The `any_of` cluster is a small variant of the `forward` cluster, but

  instead of sending the input metrics to all defined members, it sends

  each incoming metric to only one of the defined members.  The purpose of

  this is a load-balanced scenario where any of the members can receive

  any metric.  As `any_of` suggests, when any of the members become

  unreachable, the remaining available members will immediately receive

  the full input stream of metrics.  This specifically mean that when 4

  members are used, each will receive approximately 25% of the input

  metrics.  When one member becomes unavailable (e.g. network

  interruption, or a restart of the service), the remaining 3 members

  will each receive about 25% / 3 = ~8% more traffic (33%).  Alternatively,

  they will receive 1/3rd the total input.  When designing cluster

  capacity, one should take into account that in the most extreme case,

  the final remaining member will receive all input traffic.

  An `any_of` cluster can in particular be useful when the cluster

  points to other relays or caches.  When used with other relays, it

  effectively load-balances, and adapts immediately to inavailability

  of targets.  When used with caches, there is a small detail to how

  `any_of` works, that makes it very suitable.  The implementation of

  this router is not to round-robin over any available members, but

  instead it uses a consistent hashing strategy to deliver the same

  metrics to the same destination all the time.  This helps caches, and

  makes it easier to retrieve uncommitted datapoints (from a single

  cache), but still allows for a rolling restart of the caches.  When a

  member becomes unavailable, the hash destinations are not changed, but

  instead traffic destined for the unavailable node is spread evenly

  over available nodes.

* `failover` cluster

  The `failover` cluster is like the `any_of` cluster, but sticks to the

  order in which servers are defined.  This is to implement a pure

  failover scenario between servers.  All metrics are sent to at most 1

  member, so no hashing or balancing is taking place.  For example, a

  `failover` cluster with two members will only send metrics to the

  second member when the first member becomes unavailable.  As soon as

  the first member returns, all metrics are sent to the first node

  again.

* `carbon_ch` cluster

  The `carbon_ch` cluster sends the metrics to the member that is

  responsible according to the consistent hash algorithm as used in the

  original carbon python relay.  Multiple members are possible if

  replication is set to a value higher than 1.  When `dynamic` is set,

  failure of any of the servers does not result in metrics being dropped

  for that server, but instead the undeliverable metrics are sent to any

  other server in the cluster in order for the metrics not to get lost.

  This is most useful when replication is 1.

  The calculation of the hashring, that defines the way in which metrics

  are distributed, is based on the server host (or IP address) and the

  optional `instance` of the member.  This means that using `carbon_ch`

  two targets on different ports but on the same host will map to the

  same hashkey, which means no distribution of metrics takes place.  The

  instance is used to remedy that situation.  An instance is appended to

  the member after the port, and separated by an equals sign, e.g.

  `127.0.0.1:2006=a` for instance `a`.  Instances are a concept

  introduced by original python carbon-cache, and need to be used in

  accordance with the configuration of those.

  Consistent hashes are consistent in the sense that removal of a member

  from the cluster should not result in a complete re-mapping of all

  metrics to members, but instead only add the metrics from the removed

  member to all remaining members, approximately each gets its fair

  share.  The other way around, when a member is added, each member

  should see a subset of its metrics now being addressed to the new

  member.  This is an important advantage over a normal hash, where each

  removal or addition of members (also via e.g. a change in their IP

  address or hostname) would cause a full re-mapping of all metrics over

  all available metrics.

* `fnv1a_ch` cluster

  The `fnv1a_ch` cluster is an incompatible improvement to `carbon_ch`

  introduced by carbon-c-relay.  It uses a different hash technique

  (FNV1a) which is faster than the MD5-hashing used by `carbon_ch`.

  More importantly, `fnv1a_ch` clusters use both host and port to

  distinguish the members.  This is useful when multiple targets live on

  the same host just separated by port.

  Since the `instance` property is no longer necessary with `fnv1a_ch`

  this way, it is used to completely override the host:port string

  that the hashkey would be calculated off.  This is an important

  aspect, since the hashkey defines which metrics a member receives.

  Such override allows for many things, including masquerading old IP

  addresses e.g. when a machine was migrated to newer hardware.  An

  example of this would be `10.0.0.5:2003=10.0.0.2:2003` where a machine

  at address 5 now receives the metrics for a machine that were at

  address 2.

  While using instances this way can be very useful to perform

  migrations in existing clusters, for newly to setup clusters,

  instances allow to avoid this work by using an instance from day one

  to detach the machine location from the metrics it receives.  Consider

  for instance

  `10.0.0.1:2003=4d79d13554fa1301476c1f9fe968b0ac` where a random hash

  as instance is used.  This would allow to change port and/or ip

  address of the server that receives data as many times without having

  deal with any legacy being visible, assuming the random hash is

  retained.

  Note that since the instance name is used as full hash input,

  instances as `a`, `b`, etc. will likely result in poor hash

  distribution, as their hashes have very little input.  For that

  reason, consider using longer and mostly differing instance names such

  as random hashes as used in above example for better hash distribution

  behaviour.

* `jump_fnv1a_ch` cluster

  The `jump_fnv1a_ch` cluster is also a consistent hash cluster like the

  previous two, but it does not take the member host, port or instance

  into account at all.  This means this cluster type looks at the order

  in which members are defined, see also below for more on this order.

  Whether this is useful to you depends on your scenario.  In contrast

  to the previous two consistent hash cluster types, the jump hash has

  an almost perfect balancing over the members defined in the cluster.

  However, this comes at the expense of not being able to remove any

  member but the last from the cluster without causing a complete

  re-mapping of all metrics over all members.  What this basically means

  is that this hash is fine to use with constant or ever growing

  clusters where older nodes are never removed, but replaced instead.

  If you have a cluster where removal of old nodes takes place,

  the jump hash is not suitable for you.  Jump hash works with servers

  in an ordered list.  Since this order is important, it can be made

  explicit using the instance as used in previous cluster types.  When

  an instance is given with the members, it will be used as sorting key.

  Without this instance, the order will be as given in the configuration

  file, which may be prone to changes when e.g. generated by some config

  management software.

  As such, it is probably a good practice to fix the order of the

  servers with instances such that it is explicit what the right nodes

  for the jump hash are.  One can just use numbers for these, but be

  aware that sorting of 1, 2 and 10 results in 1, 10, 2, so better to

  use something like P0001, P0002, P0010 instead.

### MATCHES

Match rules are the way to direct incoming metrics to one or more

clusters.  Match rules are processed top to bottom as they are defined

in the file.  It is possible to define multiple matches in the same

rule.  Each match rule can send data to one or more clusters.  Since

match rules "fall through" unless the `stop` keyword is added,

carefully crafted match expression can be used to target

multiple clusters or aggregations.  This ability allows to replicate

metrics, as well as send certain metrics to alternative clusters with

careful ordering and usage of the `stop` keyword.  The special cluster

`blackhole` discards any metrics sent to it.  This can be useful for

weeding out unwanted metrics in certain cases.  Because throwing metrics

away is pointless if other matches would accept the same data, a match

with as destination the blackhole cluster, has an implicit `stop`.

The `validation` clause adds a check to the data (what comes after the

metric) in the form of a regular expression.  When this expression

matches, the match rule will execute as if no validation clause was

present.  However, if it fails, the match rule is aborted, and no

metrics will be sent to destinations, this is the `drop` behaviour.

When `log` is used, the metric is logged to stderr.  Care should be

taken with the latter to avoid log flooding.  When a validate clause is

present, destinations need not to be present, this allows for applying a

global validation rule.  Note that the cleansing rules are applied

before validation is done, thus the data will not have duplicate spaces.

The `route using` clause is used to perform a temporary modification to

the key used for input to the consistent hashing routines.  The primary

purpose is to route traffic so that appropriate data is sent to the

needed aggregation instances.

### REWRITES

Rewrite rules take a regular expression as input to match incoming

metrics, and transform them into the desired new metric name.  In the

replacement, backreferences are allowed to match capture groups

defined in the input regular expression.  A match of `server\.(x|y|z)\.`

allows to use e.g.  `role.\1.` in the substitution. If needed, a notation

of `\g{n}` can be used instead of `\n` where the backreference is followed

by an integer, such as `\g{1}100`.  A few caveats apply to the current

implementation of rewrite rules.  First, their location in the config

file determines when the rewrite is performed.  The rewrite is done

in-place, as such a match rule before the rewrite would match the

original name, a match rule after the rewrite no longer matches the

original name.  Care should be taken with the ordering, as multiple

rewrite rules in succession can take place, e.g. `a` gets replaced by

`b` and `b` gets replaced by `c` in a succeeding rewrite rule.  The

second caveat with the current implementation, is that the rewritten

metric names are not cleansed, like newly incoming metrics are.  Thus,

double dots and potential dangerous characters can appear if the

replacement string is crafted to produce them.  It is the responsibility

of the writer to make sure the metrics are clean.  If this is an issue

for routing, one can consider to have a rewrite-only instance that

forwards all metrics to another instance that will do the routing.

Obviously the second instance will cleanse the metrics as they come in.

The backreference notation allows to lowercase and uppercase the

replacement string with the use of the underscore (`_`) and carret

(`^`) symbols following directly after the backslash.  For example,

`role.\_1.` as substitution will lowercase the contents of `\1`.  The

dot (`.`) can be used in a similar fashion, or followed after the

underscore or caret to replace dots with underscores in the

substitution.  This can be handy for some situations where metrics are

sent to graphite.

### AGGREGATIONS

The aggregations defined take one or more input metrics expressed by one

or more regular expresions, similar to the match rules.  Incoming

metrics are aggregated over a period of time defined by the interval in

seconds.  Since events may arrive a bit later in time, the expiration

time in seconds defines when the aggregations should be considered

final, as no new entries are allowed to be added any more.  On top of an

aggregation multiple aggregations can be computed.  They can be of the

same or different aggregation types, but should write to a unique new

metric.  The metric names can include back references like in rewrite

expressions, allowing for powerful single aggregation rules that yield

in many aggregations.  When no `send to` clause is given, produced

metrics are sent to the relay as if they were submitted from the

outside, hence match and aggregation rules apply to those.  Care should

be taken that loops are avoided this way.  For this reason, the use of

the `send to` clause is encouraged, to direct the output traffic where

possible.  Like for match rules, it is possible to define multiple

cluster targets.  Also, like match rules, the `stop` keyword applies to

control the flow of metrics in the matching process.

### STATISTICS

The `send statistics to` construct is deprecated and will be removed in

the next release.  Use the special `statistics` construct instead.

The `statistics` construct can control a couple of things about the

(internal) statistics produced by the relay.  The `send to` target can

be used to avoid router loops by sending the statistics to a certain

destination cluster(s).  By default the metrics are prefixed with

`carbon.relays.`, where hostname is determinted on startup and

can be overridden using the `-H` argument.  This prefix can be set using

the `prefix with` clause similar to a rewrite rule target.  The input

match in this case is the pre-set regular expression

`^(([^.]+)(\..*)?)$` on the hostname.  As such, one can see that the

default prefix is set by `carbon.relays.\.1`.  Note that this uses the

replace-dot-with-underscore replacement feature from rewrite rules.

Given the input expression, the following match groups are available:

`\1` the entire hostname, `\2` the short hostname and `\3` the domainname

(with leading dot).  It may make sense to replace the default by

something like `carbon.relays.\_2` for certain scenarios, to always use

the lowercased short hostname, which following the expression doesn't

contain a dot.  By default, the metrics are submitted every 60 seconds,

this can be changed using the `submit every  seconds` clause

To obtain a more compatible set of values to carbon-cache.py, use the

`reset counters after interval` clause to make values non-cumulative,

that is, they will report the change compared to the previous value.

### LISTENERS

The ports and protocols the relay should listen for incoming connections

can be specified using the `listen` directive.  Currently, all listeners

need to be of `linemode` type.  An optional compression or encryption

wrapping can be specified for the port and optional interface given by

ip address, or unix socket by file.  When interface is not specified,

the any interface on all available ip protocols is assumed.  If no

`listen` directive is present, the relay will use the default listeners

for port 2003 on tcp and udp, plus the unix socket

`/tmp/.s.carbon-c-relay.2003`.  This typically expands to 5 listeners on

an IPv6 enabled system.  The default matches the behaviour of versions

prior to v3.2.

### INCLUDES

In case configuration becomes very long, or is managed better in

separate files, the `include` directive can be used to read another

file.  The given file will be read in place and added to the router

configuration at the time of inclusion.  The end result is one big route

configuration.  Multiple `include` statements can be used throughout the

configuration file.  The positioning will influence the order of rules

as normal.  Beware that recursive inclusion (`include` from an included

file) is supported, and currently no safeguards exist for an inclusion

loop.  For what is worth, this feature likely is best used with simple

configuration files (e.g. not having `include` in them).

## EXAMPLES

**carbon-c-relay** evolved over time, growing features on demand as the

tool proved to be stable and fitting the job well.  Below follow some

annotated examples of constructs that can be used with the relay.

Clusters can be defined as much as necessary.  They receive data from

match rules, and their type defines which members of the cluster finally

get the metric data.  The simplest cluster form is a `forward` cluster:

```

cluster send-through

    forward

        10.1.0.1

    ;

```

Any metric sent to the `send-through` cluster would simply be forwarded to

the server at IPv4 address `10.1.0.1`.  If we define multiple servers,

all of those servers would get the same metric, thus:

```

cluster send-through

    forward

        10.1.0.1

        10.2.0.1

    ;

```

The above results in a duplication of metrics send to both machines.

This can be useful, but most of the time it is not.  The `any_of`

cluster type is like `forward`, but it sends each incoming metric to any

of the members.  The same example with such cluster would be:

```

cluster send-to-any-one

    any_of 10.1.0.1:2010 10.1.0.1:2011;

```

This would implement a multipath scenario, where two servers are used,

the load between them is spread, but should any of them fail, all

metrics are sent to the remaining one.  This typically works well for

upstream relays, or for balancing carbon-cache processes running on the

same machine.  Should any member become unavailable, for instance due to

a rolling restart, the other members receive the traffic.  If it is

necessary to have true fail-over, where the secondary server is only

used if the first is down, the following would implement that:

```

cluster try-first-then-second

    failover 10.1.0.1:2010 10.1.0.1:2011;

```

These types are different from the two consistent hash cluster types:

```

cluster graphite

    carbon_ch

        127.0.0.1:2006=a

        127.0.0.1:2007=b

        127.0.0.1:2008=c

    ;

```

If a member in this example fails, all metrics that would go to that

member are kept in the queue, waiting for the member to return.  This

is useful for clusters of carbon-cache machines where it is desirable

that the same

metric ends up on the same server always.  The `carbon_ch` cluster type

is compatible with carbon-relay consistent hash, and can be used for

existing clusters populated by carbon-relay.  For new clusters, however,

it is better to use the `fnv1a_ch` cluster type, for it is faster, and

allows to balance over the same address but different ports without an

instance number, in constrast to `carbon_ch`.

Because we can use multiple clusters, we can also replicate without the

use of the `forward` cluster type, in a more intelligent way:

```

cluster dc-old

    carbon_ch replication 2

        10.1.0.1

        10.1.0.2

        10.1.0.3

    ;

cluster dc-new1

    fnv1a_ch replication 2

        10.2.0.1

        10.2.0.2

        10.2.0.3

    ;

cluster dc-new2

    fnv1a_ch replication 2

        10.3.0.1

        10.3.0.2

        10.3.0.3

    ;

match *

    send to dc-old

    ;

match *

    send to

        dc-new1

        dc-new2

    stop

    ;

```

In this example all incoming metrics are first sent to `dc-old`, then

`dc-new1` and finally to `dc-new2`.  Note that the cluster type of

`dc-old` is different.  Each incoming metric will be send to 2 members

of all three clusters, thus replicating to in total 6 destinations.  For

each cluster the destination members are computed independently.

Failure of clusters or members does not affect the others, since all

have individual queues.  The above example could also be written using

three match rules for each dc, or one match rule for all three dcs.  The

difference is mainly in performance, the number of times the incoming

metric has to be matched against an expression.  The `stop` rule in

`dc-new` match rule is not strictly necessary in this example, because

there are no more following match rules.  However, if the match would

target a specific subset, e.g.  `^sys\.`, and more clusters would be

defined, this could be necessary, as for instance in the following

abbreviated example:

```

cluster dc1-sys ... ;

cluster dc2-sys ... ;

cluster dc1-misc ... ;

cluster dc2-misc ... ;

match ^sys\. send to dc1-sys;

match ^sys\. send to dc2-sys stop;

match * send to dc1-misc;

match * send to dc2-misc stop;

```

As can be seen, without the `stop` in dc2-sys' match rule, all metrics

starting with `sys.` would also be send to dc1-misc and dc2-misc.  It

can be that this is desired, of course, but in this example there is a

dedicated cluster for the `sys` metrics.

Suppose there would be some unwanted metric that unfortunately is

generated, let's assume some bad/old software.  We don't want to store

this metric.  The `blackhole` cluster is suitable for that, when it is

harder to actually whitelist all wanted metrics.  Consider the

following:

```

match

        some_legacy1$

        some_legacy2$

    send to blackhole

    stop;

```

This would throw away all metrics that end with `some_legacy`, that

would otherwise be hard to filter out.  Since the order matters, it

can be used in a construct like this:

```

cluster old ... ;

cluster new ... ;

match * send to old;

match unwanted send to blackhole stop;

match * send to new;

```

In this example the old cluster would receive the metric that's unwanted

for the new cluster.  So, the order in which the rules occur does

matter for the execution.

Validation can be used to ensure the data for metrics is as expected.  A

global validation for just number (no floating point) values could be:

```

match *

    validate ^[0-9]+\ [0-9]+$ else drop

    ;

```

(Note the escape with backslash `\` of the space, you might be able to

use `\s` or `[:space:]` instead, this depends on your configured regex

implementation.)

The validation clause can exist on every match rule, so in principle,

the following is valid:

```

match ^foo

    validate ^[0-9]+\ [0-9]+$ else drop

    send to integer-cluster

    ;

match ^foo

    validate ^[0-9.e+-]+\ [0-9.e+-]+$ else drop

    send to float-cluster

    stop;

```

Note that the behaviour is different in the previous two examples.  When

no `send to` clusters are specified, a validation error makes the match

behave like the `stop` keyword is present.  Likewise, when validation

passes, processing continues with the next rule.

When destination clusters are present, the `match` respects the `stop`

keyword as normal.  When specified, processing will always stop when

specified so.  However, if validation fails, the rule does not send

anything to the destination clusters, the metric will be dropped or

logged, but never sent.

The relay is capable of rewriting incoming metrics on the fly.  This

process is done based on regular expressions with capture groups that

allow to substitute parts in a replacement string.  Rewrite rules allow

to cleanup metrics from applications, or provide a migration path.  In

it's simplest form a rewrite rule looks like this:

```

rewrite ^server\.(.+)\.(.+)\.([a-zA-Z]+)([0-9]+)

    into server.\_1.\2.\3.\3\4

    ;

```

In this example a metric like `server.DC.role.name123` would be

transformed into `server.dc.role.name.name123`.

For rewrite rules hold the same as for matches, that their order

matters.  Hence to build on top of the old/new cluster example done

earlier, the following would store the original metric name in the old

cluster, and the new metric name in the new cluster:

```

rewrite ^server\.(.+)\.(.+)\.([a-zA-Z]+)([0-9]+)

    into server.\_1.\2.\3.\3\4

    ;

rewrite ^server\.(.+)\.(.+)\.([a-zA-Z]+)([0-9]+)

    into server.\g{_1}.\g{2}.\g{3}.\g{3}\g{4}

    ;

```

The alternate syntax for backreference notation using `g\{n}` instead of `\n`

notation shown above.  Both rewrite rules are identical.

```

match * send to old;

rewrite ... ;

match * send to new;

```

Note that after the rewrite, the original metric name is no longer

available, as the rewrite happens in-place.

Aggregations are probably the most complex part of carbon-c-relay.  Two

ways of specifying aggregates are supported by carbon-c-relay.  The

first, static rules, are handled by an optimiser which tries to fold

thousands of rules into groups to make the matching more efficient.  The

second, dynamic rules, are very powerful compact definitions with

possibly thousands of internal instantiations.  A typical static

aggregation looks like:

```

aggregate

        ^sys\.dc1\.somehost-[0-9]+\.somecluster\.mysql\.replication_delay

        ^sys\.dc2\.somehost-[0-9]+\.somecluster\.mysql\.replication_delay

    every 10 seconds

    expire after 35 seconds

    timestamp at end of bucket

    compute sum write to

        mysql.somecluster.total_replication_delay

    compute average write to

        mysql.somecluster.average_replication_delay

    compute max write to

        mysql.somecluster.max_replication_delay

    compute count write to

        mysql.somecluster.replication_delay_metric_count

    ;

```

In this example, four aggregations are produced from the incoming

matching metrics.  In this example we could have written the two matches

as one, but for demonstration purposes we did not.  Obviously they can

refer to different metrics, if that makes sense.  The `every 10 seconds`

clause specifies in what interval the aggregator can expect new metrics

to arrive.  This interval is used to produce the aggregations, thus each

10 seconds 4 new metrics are generated from the data received sofar.

Because data may be in transit for some reason, or generation stalled,

the `expire after` clause specifies how long the data should be kept

before considering a data bucket (which is aggregated) to be complete.

In the example, 35 was used, which means after 35 seconds the first

aggregates are produced.  It also means that metrics can arrive 35

seconds late, and still be taken into account.  The exact time at which

the aggregate metrics are produced is random between 0 and interval (10

in this case) seconds after the expiry time.  This is done to prevent

thundering herds of metrics for large aggregation sets.

The `timestamp` that is used for the aggregations can be specified to be

the `start`, `middle` or `end` of the bucket.  Original

carbon-aggregator.py uses `start`, while carbon-c-relay's default has

always been `end`.

The `compute` clauses demonstrate a single aggregation rule can produce

multiple aggregates, as often is the case.  Internally, this comes for

free, since all possible aggregates are always calculated, whether or

not they are used.  The produced new metrics are resubmitted to the

relay, hence matches defined before in the configuration can match

output of the aggregator.  It is important to avoid loops, that can be

generated this way.  In general, splitting aggregations to their own

carbon-c-relay instance, such that it is easy to forward the produced

metrics to another relay instance is a good practice.

The previous example could also be written as follows to be dynamic:

```

aggregate

        ^sys\.dc[0-9].(somehost-[0-9]+)\.([^.]+)\.mysql\.replication_delay

    every 10 seconds

    expire after 35 seconds

    compute sum write to

        mysql.host.\1.replication_delay

    compute sum write to

        mysql.host.all.replication_delay

    compute sum write to

        mysql.cluster.\2.replication_delay

    compute sum write to

        mysql.cluster.all.replication_delay

    ;

```

Here a single match, results in four aggregations, each of a different

scope.  In this example aggregation based on hostname and cluster are

being made, as well as the more general `all` targets, which in this

example have both identical values.  Note that with this single

aggregation rule, both per-cluster, per-host and total aggregations are

produced.  Obviously, the input metrics define which hosts and clusters

are produced.

With use of the `send to` clause, aggregations can be made more

intuitive and less error-prone.  Consider the below example:

```

cluster graphite fnv1a_ch ip1 ip2 ip3;

aggregate ^sys\.somemetric

    every 60 seconds

    expire after 75 seconds

    compute sum write to

        sys.somemetric

    send to graphite

    stop

    ;

match * send to graphite;

```

It sends all incoming metrics to the graphite cluster, except the

sys.somemetric ones, which it replaces with a sum of all the incoming

ones.  Without a `stop` in the aggregate, this causes a loop, and

without the `send to`, the metric name can't be kept its original name,

for the output now directly goes to the cluster.

When configuring cluster you might want to check how the metrics will be routed

and hashed. That's what the `-t` flag is for. For the following configuration:

```

cluster graphite_swarm_odd

    fnv1a_ch replication 1

        host01.dom:2003=31F7A65E315586AC198BD798B6629CE4903D089947

        host03.dom:2003=9124E29E0C92EB63B3834C1403BD2632AA7508B740

        host05.dom:2003=B653412CD96B13C797658D2C48D952AEC3EB667313

;

cluster graphite_swarm_even

    fnv1a_ch replication 1

        host02.dom:2003=31F7A65E315586AC198BD798B6629CE4903D089947

        host04.dom:2003=9124E29E0C92EB63B3834C1403BD2632AA7508B740

        host06.dom:2003=B653412CD96B13C797658D2C48D952AEC3EB667313

;

match *

    send to

        graphite_swarm_odd

        graphite_swarm_even

    stop

;

```

Running the command:

`echo "my.super.metric" | carbon-c-relay -f config.conf  -t`, will result in:

```

[...]

match

    * -> my.super.metric

    fnv1a_ch(graphite_swarm_odd)

        host03.dom:2003

    fnv1a_ch(graphite_swarm_even)

        host04.dom:2003

    stop

```

You now know that your metric `my.super.metric` will be hashed and arrive on the

host03 and host04 machines.  Adding the `-d` flag will increase the amount of

information by showing you the hashring

## STATISTICS

When **carbon-c-relay** is run without `-d` or `-s` arguments,

statistics will be produced.  By default they are sent to the relay

itself in the form of `carbon.relays..*`.  See the

`statistics` construct to override this prefix, sending interval and

values produced.  While many metrics have a similar name to what

carbon-cache.py would produce, their values are likely different.  By

default, most values are running counters which only increase over time.

The use of the nonNegativeDerivative() function from graphite is useful

with these.

The following metrics are produced under the `carbon.relays.`

namespace:

* metricsReceived

  The number of metrics that were received by the relay.  Received here

  means that they were seen and processed by any of the dispatchers.

* metricsSent

  The number of metrics that were sent from the relay.  This is a total

  count for all servers combined.  When incoming metrics are duplicated

  by the cluster configuration, this counter will include all those

  duplications.  In other words, the amount of metrics that were

  successfully sent to other systems.  Note that metrics that are

  processed (received) but still in the sending queue (queued) are not

  included in this counter.

* metricsDiscarded

  The number of input lines that were not considered to be a valid

  metric.  Such lines can be empty, only containing whitespace, or

  hitting the limits given for max input length and/or max metric length

  (see `-m` and `-M` options).

* metricsQueued

  The total number of metrics that are currently in the queues for all

  the server targets.  This metric is not cumulative, for it is a sample

  of the queue size, which can (and should) go up and down.  Therefore

  you should not use the derivative function for this metric.

* metricsDropped

  The total number of metric that had to be dropped due to server queues

  overflowing.  A queue typically overflows when the server it tries to

  send its metrics to is not reachable, or too slow in ingesting the

  amount of metrics queued.  This can be network or resource related,

  and also greatly depends on the rate of metrics being sent to the

  particular server.

* metricsBlackholed

  The number of metrics that did not match any rule, or matched a rule

  with blackhole as target.  Depending on your configuration, a high

  value might be an indication of a misconfiguration somewhere.  These

  metrics were received by the relay, but never sent anywhere, thus they

  disappeared.

* metricStalls

  The number of times the relay had to stall a client to indicate that

  the downstream server cannot handle the stream of metrics.  A stall is

  only performed when the queue is full and the server is actually

  receptive of metrics, but just too slow at the moment.  Stalls

  typically happen during micro-bursts, where the client typically is

  unaware that it should stop sending more data, while it is able to.

* connections

  The number of connect requests handled.  This is an ever increasing

  number just counting how many connections were accepted.

* disconnects

  The number of disconnected clients.  A disconnect either happens

  because the client goes away, or due to an idle timeout in the relay.

  The difference between this metric and connections is the amount of

  connections actively held by the relay.  In normal situations this

  amount remains within reasonable bounds.  Many connections, but few

  disconnections typically indicate a possible connection leak in the

  client.  The idle connections disconnect in the relay here is to guard

  against resource drain in such scenarios.

* dispatch\_wallTime\_us

  The number of microseconds spent by the dispatchers to do their work.

  In particular on multi-core systems, this value can be confusing,

  however, it indicates how long the dispatchers were doing work

  handling clients.  It includes everything they do, from reading data

  from a socket, cleaning up the input metric, to adding the metric to

  the appropriate queues.  The larger the configuration, and more

  complex in terms of matches, the more time the dispatchers will spend

  on the cpu.  But also time they do /not/ spend on the cpu is included

  in this number.  It is the pure wallclock time the dispatcher was

  serving a client.

* dispatch\_sleepTime\_us

  The number of microseconds spent by the dispatchers sleeping waiting

  for work.  When this value gets small (or even zero) the dispatcher

  has so much work that it doesn't sleep any more, and likely can't

  process the work in a timely fashion any more.  This value plus the

  wallTime from above sort of sums up to the total uptime taken by this

  dispatcher.  Therefore, expressing the wallTime as percentage of this

  sum gives the busyness percentage draining all the way up to 100% if

  sleepTime goes to 0.

* server\_wallTime\_us

  The number of microseconds spent by the servers to send the metrics

  from their queues.  This value includes connection creation, reading

  from the queue, and sending metrics over the network.

* dispatcherX

  For each indivual dispatcher, the metrics received and blackholed plus

  the wall clock time.  The values are as described above.

* destinations.X

  For all known destinations, the number of dropped, queued and sent

  metrics plus the wall clock time spent.  The values are as described

  above.

* aggregators.metricsReceived

  The number of metrics that were matched an aggregator rule and were

  accepted by the aggregator.  When a metric matches multiple

  aggregators, this value will reflect that.  A metric is not counted

  when it is considered syntactically invalid, e.g. no value was found.

* aggregators.metricsDropped

  The number of metrics that were sent to an aggregator, but did not fit

  timewise.  This is either because the metric was too far in the past

  or future.  The expire after clause in aggregate statements controls

  how long in the past metric values are accepted.

* aggregators.metricsSent

  The number of metrics that were sent from the aggregators.  These

  metrics were produced and are the actual results of aggregations.

## BUGS

Please report them at:

## AUTHOR

Fabian Groffen <[email protected]>

## SEE ALSO

All other utilities from the graphite stack.

This project aims to be a fast replacement of the original

[Carbon relay](http://graphite.readthedocs.org/en/1.0/carbon-daemons.html#carbon-relay-py).

**carbon-c-relay** aims to deliver performance and configurability.

Carbon is single threaded, and sending metrics to multiple

consistent-hash clusters requires chaining of relays.  This project

provides a multithreaded relay which can address multiple targets and

clusters for each and every metric based on pattern matches.

There are a couple more replacement projects out there, which

are [carbon-relay-ng](https://github.com/graphite-ng/carbon-relay-ng) and

[graphite-relay](https://github.com/markchadwick/graphite-relay).

Compared to carbon-relay-ng, this project does provide carbon's

consistent-hash routing.  graphite-relay, which does this, however

doesn't do metric-based matches to direct the traffic, which this

project does as well.  To date, carbon-c-relay can do aggregations,

failover targets and more.

## ACKNOWLEDGEMENTS

This program was originally developed for Booking.com, which approved

that the code was published and released as Open Source on GitHub, for

which the author would like to express his gratitude.

Development has continued since with the help of many contributors

suggesting features, reporting bugs, adding patches and more to make

carbon-c-relay into what it is today.