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https://github.com/ClusterLabs/PAF

PostgreSQL Automatic Failover: High-Availibility for Postgres, based on Pacemaker and Corosync.
https://github.com/ClusterLabs/PAF

failover high-availability pacemaker paf postgres postgresql resource-agent

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PostgreSQL Automatic Failover: High-Availibility for Postgres, based on Pacemaker and Corosync.

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# PostgreSQL Automatic Failover



High-Availibility for Postgres, based on industry references Pacemaker and

Corosync.



## Description



Pacemaker is nowadays the industry reference for High Availability. In the same

fashion than for Systemd, all Linux distributions moved (or are moving) to this

unique Pacemaker+Corosync stack, removing all other existing high availability

stacks (CMAN, RGManager, OpenAIS, ...). It is able to detect failure on various

services and automatically decide to failover the failing resource to another

node when possible.



To be able to manage a specific service resource, Pacemaker interact with it

through a so-called "Resource Agent". Resource agents must comply to the OCF

specification which define what they must implement (start, stop, promote,

etc), how they should behave and inform Pacemaker of their results.



PostgreSQL Automatic Failover is a new OCF resource Agent dedicated to

PostgreSQL. Its original wish is to keep a clear limit between the Pacemaker

administration and the PostgreSQL one, to keep things simple, documented and

yet powerful.



Once your PostgreSQL cluster built using internal streaming replication, PAF is

able to expose to Pacemaker what is the current status of the PostgreSQL

instance on each node: master, slave, stopped, catching up, etc. Should a

failure occurs on the master, Pacemaker will try to recover it by default.

Should the failure be non-recoverable, PAF allows the slaves to be able to

elect the best of them (the closest one to the old master) and promote it as

the new master. All of this thanks to the robust, feature-full and most

importantly experienced project: Pacemaker.



For information about how to install this agent, see `INSTALL.md`.



## Setup and requirements



PAF supports PostgreSQL 9.3 and higher. It has been extensively tested under

CentOS 6 and 7 in various scenario.



PAF has been written to give to the administrator the maximum control

over their PostgreSQL configuration and architecture. Thus, you are 100%

responsible for the master/slave creations and their setup. The agent

will NOT edit your setup. It only requires you to follow these pre-requisites:



  * slave __must__ be in hot_standby (accept read-only connections) ;

  * the following parameters __must__ be configured in the appropriate place :

    * `standby_mode = on` (for PostgreSQL 11 and before)

    * `recovery_target_timeline = 'latest'`

    * `primary_conninfo` wih `application_name` set to the node name as seen

      in Pacemaker.

  * these last parameters has been merged inside the instance configuration

    file with PostgreSQL 12. For PostgreSQL 11 and before, you __must__

    provide a `recovery.conf` template file.



When setting up the resource in Pacemaker, here are the available parameters you

can set:



  * `bindir`: location of the PostgreSQL binaries (default: `/usr/bin`)

  * `pgdata`: location of the PGDATA of your instance (default:

    `/var/lib/pgsql/data`)

  * `datadir`: path to the directory set in `data_directory` from your

    postgresql.conf file. This parameter has same default than PostgreSQL

    itself: the `pgdata` parameter value. Unless you have a special PostgreSQL

    setup and you understand this parameter, __ignore it__

  * `pghost`: the socket directory or IP address to use to connect to the

    local instance (default: `/tmp` or `/var/run/postgresql` for DEBIAN)

  * `pgport`:  the port to connect to the local instance (default: `5432`)

  * `recovery_template`: __only__ for PostgreSQL 11 and before. The local 

    template that will be copied as the `PGDATA/recovery.conf` file. This

    file must not exist on any node for PostgreSQL 12 and after.

    (default: `$PGDATA/recovery.conf.pcmk`)

  * `start_opts`: Additional arguments given to the postgres process on startup.

    See "postgres --help" for available options. Useful when the postgresql.conf

    file is not in the data directory (PGDATA), eg.:

    `-c config_file=/etc/postgresql/9.3/main/postgresql.conf`

  * `system_user`: the system owner of your instance's process (default:

    `postgres`)

  * `maxlag`: maximum lag allowed on a standby before we set a negative master

    score on it. The calculation is based on the difference between the current

    xlog location on the master and the write location on the standby.

    (default: 0, which disables this feature)



For a demonstration about how to setup a cluster, see

[http://clusterlabs.github.io/PAF/documentation.html](http://clusterlabs.github.io/PAF/documentation.html).