postgresql_cluster

PostgreSQL High-Availability Cluster :elephant: :sparkling_heart:

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Production-ready PostgreSQL High-Availability Cluster (based on Patroni). Automating with Ansible.

postgresql_cluster automates the deployment and management of highly available PostgreSQL clusters in production environments. This solution is tailored for use on dedicated physical servers, virtual machines, and within both on-premises and cloud-based infrastructures.

You can find a version of this documentation that is searchable and also easier to navigate at postgresql-cluster.org

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Supported setups of Postgres Cluster

postgresql_cluster

You have three schemes available for deployment:

1. PostgreSQL High-Availability only

This is simple scheme without load balancing.

Components of high availability:

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, etcd, Consul or Kubernetes. Used for automate the management of PostgreSQL instances and auto failover.
etcd is a distributed reliable key-value store for the most critical data of a distributed system. etcd is written in Go and uses the Raft consensus algorithm to manage a highly-available replicated log. It is used by Patroni to store information about the status of the cluster and PostgreSQL configuration parameters. What is Distributed Consensus?
vip-manager (optional, if the cluster_vip variable is specified) is a service that gets started on all cluster nodes and connects to the DCS. If the local node owns the leader-key, vip-manager starts the configured VIP. In case of a failover, vip-manager removes the VIP on the old leader and the corresponding service on the new leader starts it there. Used to provide a single entry point (VIP) for database access.
PgBouncer (optional, if the pgbouncer_install variable is true) is a connection pooler for PostgreSQL.

2. PostgreSQL High-Availability with Load Balancing

This scheme enables load distribution for read operations and also allows for scaling out the cluster with read-only replicas.

When deploying to cloud providers such as AWS, GCP, Azure, DigitalOcean, and Hetzner Cloud, a cloud load balancer is automatically created by default to provide a single entry point to the database (controlled by the cloud_load_balancer variable).

For non-cloud environments, such as when deploying on Your Own Machines, the HAProxy load balancer is available for use. To enable it, set with_haproxy_load_balancing: true in the vars/main.yml file.

:heavy_exclamation_mark: Note: Your application must have support sending read requests to a custom port 5001, and write requests to port 5000.

port 5000 (read / write) master
port 5001 (read only) all replicas

if variable "synchronous_mode" is 'true' (vars/main.yml):

port 5002 (read only) synchronous replica only
port 5003 (read only) asynchronous replicas only

Components of HAProxy load balancing:

HAProxy is a free, very fast and reliable solution offering high availability, load balancing, and proxying for TCP and HTTP-based applications.
confd manage local application configuration files using templates and data from etcd or consul. Used to automate HAProxy configuration file management.
Keepalived (optional, if the cluster_vip variable is specified) provides a virtual high-available IP address (VIP) and single entry point for databases access. Implementing VRRP (Virtual Router Redundancy Protocol) for Linux. In our configuration keepalived checks the status of the HAProxy service and in case of a failure delegates the VIP to another server in the cluster.

3. PostgreSQL High-Availability with Consul Service Discovery

To use this scheme, specify dcs_type: consul in variable file vars/main.yml

This scheme is suitable for master-only access and for load balancing (using DNS) for reading across replicas. Consul Service Discovery with DNS resolving is used as a client access point to the database.

Client access point (example):

master.postgres-cluster.service.consul
replica.postgres-cluster.service.consul

Besides, it can be useful for a distributed cluster across different data centers. We can specify in advance which data center the database server is located in and then use this for applications running in the same data center.

Example: replica.postgres-cluster.service.dc1.consul, replica.postgres-cluster.service.dc2.consul

It requires the installation of a consul in client mode on each application server for service DNS resolution (or use forward DNS to the remote consul server instead of installing a local consul client).

Compatibility

RedHat and Debian based distros (x86_64)

Supported Linux Distributions:

Debian: 11, 12
Ubuntu: 22.04, 24.04
CentOS Stream: 9
Oracle Linux: 8, 9
Rocky Linux: 8, 9
AlmaLinux: 8, 9

PostgreSQL versions:

all supported PostgreSQL versions

:white_check_mark: tested, works fine: PostgreSQL 10, 11, 12, 13, 14, 15, 16

Table of results of daily automated testing of cluster deployment:

Distribution	Test result
Debian 11
Debian 12
Ubuntu 22.04
Ubuntu 24.04
CentOS Stream 9
Oracle Linux 8
Oracle Linux 9
Rocky Linux 8
Rocky Linux 9
AlmaLinux 8
AlmaLinux 9

Ansible version

Minimum supported Ansible version: 8.0.0 (ansible-core 2.15.0)

Requirements

Click here to expand...

This playbook requires root privileges or sudo.

Ansible (What is Ansible?)

if dcs_type: "consul", please install consul role requirements on the control node:

ansible-galaxy install -r roles/consul/requirements.yml

Port requirements

List of required TCP ports that must be open for the database cluster:

5432 (postgresql)
6432 (pgbouncer)
8008 (patroni rest api)
2379, 2380 (etcd)

for the scheme "[Type A] PostgreSQL High-Availability with Load Balancing":

5000 (haproxy - (read/write) master)
5001 (haproxy - (read only) all replicas)
5002 (haproxy - (read only) synchronous replica only)
5003 (haproxy - (read only) asynchronous replicas only)
7000 (optional, haproxy stats)

for the scheme "[Type C] PostgreSQL High-Availability with Consul Service Discovery (DNS)":

8300 (Consul Server RPC)
8301 (Consul Serf LAN)
8302 (Consul Serf WAN)
8500 (Consul HTTP API)
8600 (Consul DNS server)

Recommenations

Click here to expand...

linux (Operation System):

Update your operating system on your target servers before deploying;

Make sure you have time synchronization is configured (NTP). Specify ntp_enabled:'true' and ntp_servers if you want to install and configure the ntp service.

DCS (Distributed Consensus Store):

Fast drives and a reliable network are the most important factors for the performance and stability of an etcd (or consul) cluster.

Avoid storing etcd (or consul) data on the same drive along with other processes (such as the database) that are intensively using the resources of the disk subsystem! Store the etcd and postgresql data on different disks (see etcd_data_dir, consul_data_path variables), use ssd drives if possible. See hardware recommendations and tuning guides.

It is recommended to deploy the DCS cluster on dedicated servers, separate from the database servers.

Placement of cluster members in different data centers:

If you’d prefer a cross-data center setup, where the replicating databases are located in different data centers, etcd member placement becomes critical.

There are quite a lot of things to consider if you want to create a really robust etcd cluster, but there is one rule: do not placing all etcd members in your primary data center. See some examples.

How to prevent data loss in case of autofailover (synchronous_modes):

Due to performance reasons, a synchronous replication is disabled by default.

To minimize the risk of losing data on autofailover, you can configure settings in the following way:

synchronous_mode: 'true'
synchronous_mode_strict: 'true'
synchronous_commit: 'on' (or 'remote_apply')

Getting Started

To run the PostgreSQL Cluster Console, execute the following command:

docker run -d --name pg-console \
  --publish 80:80 \
  --publish 8080:8080 \
  --env PG_CONSOLE_API_URL=http://localhost:8080/api/v1 \
  --env PG_CONSOLE_AUTHORIZATION_TOKEN=secret_token \
  --volume console_postgres:/var/lib/postgresql \
  --volume /var/run/docker.sock:/var/run/docker.sock \
  --volume /tmp/ansible:/tmp/ansible \
  --restart=unless-stopped \
  vitabaks/postgresql_cluster_console:2.0.0

Note: It is recommended to run the console in the same network as your database servers to enable monitoring of the cluster status. In this case, replace localhost with your server's IP address in the PG_CONSOLE_API_URL variable.

Open the Console UI

Go to http://localhost/ and use secret_token for authorization.

Note: If you have set up the console on a different server, replace 'localhost' with the server's address. Use the value of your token if you have redefined it in the PG_CONSOLE_AUTHORIZATION_TOKEN variable.

Click here to expand... if you prefer the command line.

Command line

Install Ansible on one control node (which could easily be a laptop)

sudo apt update && sudo apt install -y python3-pip sshpass git
pip3 install ansible

Download or clone this repository

git clone https://github.com/vitabaks/postgresql_cluster.git

Go to the playbook directory

cd postgresql_cluster/automation

Edit the inventory file

Specify (non-public) IP addresses and connection settings (`ansible_user`, `ansible_ssh_pass` or `ansible_ssh_private_key_file` for your environment

nano inventory

Edit the variable file vars/main.yml

nano vars/main.yml

Minimum set of variables:

proxy_env # if required (for download packages)
cluster_vip # for client access to databases in the cluster (optional)
patroni_cluster_name
postgresql_version
postgresql_data_dir
with_haproxy_load_balancing 'true' (Type A) or 'false'/default (Type B)
dcs_type # "etcd" (default) or "consul" (Type C)

See the vars/main.yml, system.yml and (Debian.yml or RedHat.yml) files for more details.

if dcs_type: "consul", please install consul role requirements on the control node:

ansible-galaxy install -r roles/consul/requirements.yml

Try to connect to hosts

ansible all -m ping

Run playbook:

ansible-playbook deploy_pgcluster.yml

Deploy Cluster with TimescaleDB

To deploy a PostgreSQL High-Availability Cluster with the TimescaleDB extension, you just need to add the enable_timescale variable.

Example:

ansible-playbook deploy_pgcluster.yml -e "enable_timescale=true"

How to start from scratch

If you need to start from the very beginning, you can use the playbook remove_cluster.yml.

Available variables:

remove_postgres: stop the PostgreSQL service and remove data.
remove_etcd: stop the ETCD service and remove data.
remove_consul: stop the Consul service and remove data.

Run the following command to remove specific components:

ansible-playbook remove_cluster.yml -e "remove_postgres=true remove_etcd=true"

This command will delete the specified components, allowing you to start a new installation from scratch.

:warning: Caution: be careful when running this command in a production environment.

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