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https://github.com/elasticio/haproxy-srv

Flexible HAProxy auto configuration and auto service discovery for SkyDNS or Mesos-DNS
https://github.com/elasticio/haproxy-srv

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Flexible HAProxy auto configuration and auto service discovery for SkyDNS or Mesos-DNS

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# HAProxy SRV



HAProxy-SRV is a templating solution that can flexibly reconfigure HAProxy based on the regular polling of the

service data from DNS (e.g. SkyDNS or Mesos-DNS) using SRV records.



HAProxy-SRV also works with Round-Robin DNS A records, like Docker Swarm Mode.



It has a very simple logic - HA Proxy is configured based on the Handlebars template that is re-evaluated every time changes in DNS are detecting. Script is polling DNS and trigger a HA Proxy configuration refresh after changes.



Made by [elastic.io](http://www.elastic.io) in Germany.



# Quick start



Simplest way to start it with Docker:



```

docker run -d -p 8080:8080 -p 80:80 -v $PWD/haproxy.cfg.template:/src/haproxy.cfg.template elasticio/haproxy-srv:latest

```



if you want to see more DEBUG output then just add ``-e "DEBUG=*"``



# How it works



Script works very simple - after docker container started script parse and validates template, create a HAProxy configuration file in ``/src/haproxy.cfg`` and start HAProxy as a daemon. Every second (by default, can be configured via ``REFRESH_TIMEOUT`` env variable, default 1000) scirpt will execute a DNS lookup and re-evaluate the template, if result of evaluation is different from original configuration, original config will be overwritten and HAProxy reload will be triggered. HAProxy reload will not affect existing connections.



# How to use it



Recommended way to deploy is is to use [a Docker image](https://hub.docker.com/r/elasticio/haproxy-srv/). You would need to place your configuration file template, the simples way to do it is to build an image based on ``haproxy-srv`` image. 



Create a new ``Dockerfile`` content like this:



```

FROM elasticio/haproxy-srv:latest



COPY haproxy.cfg.template /src/



EXPOSE 80 8880

```



Note the ``EXPOSE`` part here, don't forget to specify exposed ports if your HAProxy configuration listens on any port different from ``80``.



As a next step create a template file, it should be placed under ``/src/haproxy.cfg.template`` in resulting Docker container and should have a [Handlebars](http://handlebarsjs.com/) syntax with one little extension (see below). Here is the sample:



```hbs

global

    user root

    group root



    # Stats required for this module to work

    # https://github.com/observing/haproxy#haproxycfg

    stats socket /tmp/haproxy.sock level admin



defaults

    mode    http

    timeout connect 5000

    timeout client  50000

    timeout server  50000



{{#dns-srv "_frontend._tcp.marathon.mesos"}}

    frontend sample

        bind 0.0.0.0:80

        balance roundrobin

        option http-server-close

        option forwardfor

        {{#each this}}

            server frontend-{{@index}} {{ip}}:{{port}} check weight {{weight}}

        {{/each}}

{{/dns-srv}}



# Standard DNS Round-Robin

{{#dns-a "cluster.example.com"}}

  frontend sample2

    bind 0.0.0.0:8080

    {{#each this}}

      server {{name}} {{ip}}:80 check

    {{/each}}

{{/dns-a}}



# Docker Swarm Mode example

{{#dns-a "tasks.myservice"}}

  frontend sample3

    bind 0.0.0.0:8081

    {{#each this}}

      server {{name}} {{ip}}:80 check

    {{/each}}

{{/dns-a}}

```



It could be any valid HAProxy configuration with one mandatory addition:



```

stats socket /tmp/haproxy.sock level admin

```



to trigger HAProxy restart the script inside the file will communicate with HAProxy daemon via socket ```/tmp/haproxy.sock```.



# Template



Configuration template is a normal [Handlebars](http://handlebarsjs.com/) so that you could use any of the feature of this template language. There is however one additional helper ``dns-srv`` implemented. This helper takes one string parameter and will execute a [DNS SRV lookup](https://nodejs.org/api/dns.html#dns_dns_resolvesrv_hostname_callback) to fetch an SRV record(s). After SRV Record lookup, for each SRV record a [DNS resolution](https://nodejs.org/api/dns.html#dns_dns_resolve_hostname_rrtype_callback) to find the IP will be made.



This template will give you an idea how to use it:



```hbs

# Your usual configuration is here

{{#dns-srv "_frontend._tcp.marathon.mesos"}}

    # This block will only be rendered when _frontend._tcp.marathon.mesos was found in DNS

    {{#each this}}

        # This piece will be rendered for each SRV entry from DNS

        SRV Name is {{name}}

        SRV Weight is {{weight}}

        SRV Port is {{port}}

        IP for SRV Name is {{ip}}

    {{/each}}

{{/dns-srv}}

# rest of your configuration

```



Typical use-case for Msos-DNS you can see above.



# Docker Swarm Mode Guide



First, create a network, and web service:



```

$ docker network create -d overlay --subnet 10.1.1.0/24 my_net

$ docker service create --replicas 2 --name my_web --network my_net nginx

```



By default, services are created as `--endpoint-mode vip`.  If you use VIP mode,

then the Round-Robin DNS name is `tasks.my_web`.  If you use `--endpoint-mode dnsrr`

then the `my_web` DNS name will work in the HAProxy `dns-a` template.



Follow the **How to use it** section above on creating a new proxy image using

a custom haproxy.cfg.template.  For the `dns-a` section use:



```

{{#dns-a "tasks.my_web"}}

  # other configs

  backend my_web

  {{#each this}}

    server {{name}} {{ip}}:80 check

  {{/each}}

{{/dns-a}}

```



```

$ mkdir my_proxy ; cd my_proxy

#  (make a new Dockerfile)

$ docker build -t my_proxy_image .

```



Fire up a new proxy, publishing port 80 to something unique on each docker host node



```

$ docker service create --name my_proxy --network my_net -p 8081:80 my_proxy_image

```



Optionally, use some other method for sharing & binding the haproxy.cfg.template file

into the `elasticio/haproxy-srv` image.



# Debugging



Just set the ``DEBUG`` environment variable into ``*`` to see detailed logging.



# TODOs



PRs are welcome for

 * Bug fixes

 * Unit tests

 * Gulp or Grunt-based builds

 * CircleCI config for continous integration