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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
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.
Currently supported PostgreSQL versions: 9.3 to 13.
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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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/>__
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
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.
Pre-requirements for Mac OS
To install requirements on a Mac, run the following:
brew install postgresql etcd haproxy libyaml python
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:
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
pip install psycopg2-binary
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 or etcd3
python-etcd module in order to use Etcd as DCS
python-consul module in order to use Consul as DCS
kazoo module in order to use Zookeeper as DCS
kazoo module in order to use Exhibitor as DCS (same dependencies as for Zookeeper)
kubernetes module in order to use Kubernetes as DCS in Patroni
pysyncobj module in order to use python Raft implementation as DCS
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.
To get started, do the following from different terminals: ::
> etcd --data-dir=data/etcd --enable-v2=true > ./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.
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,
> haproxy -f haproxy.cfg
> psql --host 127.0.0.1 --port 5000 postgres
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
here <https://github.com/zalando/patroni/blob/master/docs/ENVIRONMENT.rst>__ for comprehensive information about configuring(overriding) settings via environment variables.
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.
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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