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Patroni: A Template for PostgreSQL HA with ZooKeeper, etcd or Consul

You can find a version of this documentation that is searchable and also easier to navigate at patroni.readthedocs.io <https://patroni.readthedocs.io>__.

There are many ways to run high availability with PostgreSQL; for a list, see the PostgreSQL Documentation <https://wiki.postgresql.org/wiki/Replication,_Clustering,_and_Connection_Pooling>__.

Patroni is a template for you to create your own customized, high-availability solution using Python and - for maximum accessibility - a distributed configuration store like ZooKeeper <https://zookeeper.apache.org/>, etcd <https://github.com/coreos/etcd>, Consul <https://github.com/hashicorp/consul>__ or Kubernetes <https://kubernetes.io>__. Database engineers, DBAs, DevOps engineers, and SREs who are looking to quickly deploy HA PostgreSQL in the datacenter-or anywhere else-will hopefully find it useful.

We call Patroni a "template" because it is far from being a one-size-fits-all or plug-and-play replication system. It will have its own caveats. Use wisely.

Note to Kubernetes users: Patroni can run natively on top of Kubernetes. Take a look at the Kubernetes <https://github.com/zalando/patroni/blob/master/docs/kubernetes.rst>__ chapter of the Patroni documentation.

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=================
How Patroni Works

Patroni originated as a fork of Governor <https://github.com/compose/governor>__, the project from Compose. It includes plenty of new features.

For an example of a Docker-based deployment with Patroni, see Spilo <https://github.com/zalando/spilo>__, currently in use at Zalando.

For additional background info, see:

• Elephants on Automatic: HA Clustered PostgreSQL with Helm <https://www.youtube.com/watch?v=CftcVhFMGSY>_, talk by Josh Berkus and Oleksii Kliukin at KubeCon Berlin 2017
• PostgreSQL HA with Kubernetes and Patroni <https://www.youtube.com/watch?v=iruaCgeG7qs>__, talk by Josh Berkus at KubeCon 2016 (video)
• Feb. 2016 Zalando Tech blog post <https://tech.zalando.de/blog/zalandos-patroni-a-template-for-high-availability-postgresql/>__

==================
Development Status

Patroni is in active development and accepts contributions. See our Contributing <https://github.com/zalando/patroni/blob/master/docs/CONTRIBUTING.rst>__ section below for more details.

We report new releases information here <https://github.com/zalando/patroni/releases>__.

=========
Community

There are two places to connect with the Patroni community: on github <https://github.com/zalando/patroni>, via Issues and PRs, and on channel #patroni in the PostgreSQL Slack <https://postgres-slack.herokuapp.com/>. If you're using Patroni, or just interested, please join us.

===================================
Technical Requirements/Installation

Pre-requirements for Mac OS

To install requirements on a Mac, run the following:

::

brew install postgresql etcd haproxy libyaml python

Psycopg2

Starting from psycopg2-2.8 <http://initd.org/psycopg/articles/2019/04/04/psycopg-28-released/>__ the binary version of psycopg2 will no longer be installed by default. Installing it from the source code requires C compiler and postgres+python dev packages.
Since in the python world it is not possible to specify dependency as psycopg2 OR psycopg2-binary you will have to decide how to install it.

There are a few options available:

1. Use the package manager from your distro

::

sudo apt-get install python-psycopg2   # install python2 psycopg2 module on Debian/Ubuntu
sudo apt-get install python3-psycopg2  # install python3 psycopg2 module on Debian/Ubuntu
sudo yum install python-psycopg2       # install python2 psycopg2 on RedHat/Fedora/CentOS

2. Install psycopg2 from the binary package

::

pip install psycopg2-binary

3. Install psycopg2 from source

::

pip install psycopg2>=2.5.4

General installation for pip

Patroni can be installed with pip:

::

pip install patroni[dependencies]

where dependencies can be either empty, or consist of one or more of the following:

etcd
python-etcd module in order to use Etcd as DCS
consul
python-consul module in order to use Consul as DCS
zookeeper
kazoo module in order to use Zookeeper as DCS
exhibitor
kazoo module in order to use Exhibitor as DCS (same dependencies as for Zookeeper)
kubernetes
kubernetes module in order to use Kubernetes as DCS in Patroni
aws
boto in order to use AWS callbacks

For example, the command in order to install Patroni together with dependencies for Etcd as a DCS and AWS callbacks is:

::

pip install patroni[etcd,aws]

Note that external tools to call in the replica creation or custom bootstap scripts (i.e. WAL-E) should be installed independently of Patroni.

=======================
Running and Configuring

To get started, do the following from different terminals:
::

> etcd --data-dir=data/etcd
> ./patroni.py postgres0.yml
> ./patroni.py postgres1.yml

You will then see a high-availability cluster start up. Test different settings in the YAML files to see how the cluster's behavior changes. Kill some of the components to see how the system behaves.

Add more postgres*.yml files to create an even larger cluster.

Patroni provides an HAProxy <http://www.haproxy.org/>__ configuration, which will give your application a single endpoint for connecting to the cluster's leader. To configure,
run:

::

> haproxy -f haproxy.cfg

::

> psql --host 127.0.0.1 --port 5000 postgres

==================
YAML Configuration

Go here <https://github.com/zalando/patroni/blob/master/docs/SETTINGS.rst>__ for comprehensive information about settings for etcd, consul, and ZooKeeper. And for an example, see postgres0.yml <https://github.com/zalando/patroni/blob/master/postgres0.yml>__.

=========================
Environment Configuration

Go here <https://github.com/zalando/patroni/blob/master/docs/ENVIRONMENT.rst>__ for comprehensive information about configuring(overriding) settings via environment variables.

===================
Replication Choices

Patroni uses Postgres' streaming replication, which is asynchronous by default. Patroni's asynchronous replication configuration allows for maximum_lag_on_failover settings. This setting ensures failover will not occur if a follower is more than a certain number of bytes behind the leader. This setting should be increased or decreased based on business requirements. It's also possible to use synchronous replication for better durability guarantees. See replication modes documentation <https://github.com/zalando/patroni/blob/master/docs/replication_modes.rst>__ for details.

======================================
Applications Should Not Use Superusers

When connecting from an application, always use a non-superuser. Patroni requires access to the database to function properly. By using a superuser from an application, you can potentially use the entire connection pool, including the connections reserved for superusers, with the superuser_reserved_connections setting. If Patroni cannot access the Primary because the connection pool is full, behavior will be undesirable.

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