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Community Blog How to Set Up a Highly Available PostgreSQL Cluster Using Patroni on Ubuntu 16.04

How to Set Up a Highly Available PostgreSQL Cluster Using Patroni on Ubuntu 16.04

In this tutorial, we will be configuring a highly available PostgreSQL cluster using Patroni on Alibaba Cloud Elastic Compute Service (ECS) with Ubuntu 16.

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By Hitesh Jethva, Alibaba Cloud Tech Share Author. Tech Share is Alibaba Cloud's incentive program to encourage the sharing of technical knowledge and best practices within the cloud community.

Patroni is an open source tool that can be used for creating and managing your own customized, high-availability cluster for PostgreSQL with Python. It can be used to handle tasks such as replication, backups and restorations. Patroni also provides an HAProxy configuration, giving your application a single endpoint for connecting to the cluster's leader. If you are looking to quickly deploy HA PostgreSQL cluster in the data center, then Patroni is definitely worth considering.

In this tutorial, we will be configuring a highly available PostgreSQL cluster using Patroni on Alibaba Cloud Elastic Compute Service (ECS) with Ubuntu 16.04. We will need four ECS instances; we will use Instance1 as a master and Instance2 as a slave, configure replication from master to slaves, and configure automatically failover to the slave if the master goes down.

Prerequisites

  • Four fresh Alibaba cloud instance with Ubuntu 16.04 installed.
  • A static IP address is configured on each instance.
  • A root password is set up to your instance.

Launch Alibaba Cloud ECS Instance

First, log in to your Alibaba Cloud ECS Console. Create a new ECS instance, choosing Ubuntu 16.04 as the operating system with at least 2GB RAM. Connect to your ECS instance and log in as the root user.

Once you are logged into your Ubuntu 16.04 instance, run the following command to update your base system with the latest available packages.

apt-get update -y

Setup Environment

In this tutorial, we will be using the following setup:

Instance Application IP Address
Instance1 Postgres, Patroni 192.168.0.105
Instance2 Postgres, Patroni 192.168.0.104
Instance3 etcd 192.168.0.103
Instance4 HAProxy 192.168.0.102

Install PostgreSQL

First, you will need to install PostgreSQL on Instance1 and Instance2. By default, PostgreSQL is available in the Ubuntu 16.04 repository. You can install it by just running the following command:

apt-get install postgresql -y

Once the installation is completed, verify the status of PostgreSQL using the following command:

systemctl status postgresql

Output:

● postgresql.service - PostgreSQL RDBMS
   Loaded: loaded (/lib/systemd/system/postgresql.service; enabled; vendor preset: enabled)
   Active: active (exited) since Fri 2018-09-21 20:03:04 IST; 1min 7s ago
 Main PID: 3994 (code=exited, status=0/SUCCESS)
   CGroup: /system.slice/postgresql.service

Sep 21 20:03:04 Node1 systemd[1]: Starting PostgreSQL RDBMS...
Sep 21 20:03:04 Node1 systemd[1]: Started PostgreSQL RDBMS.
Sep 21 20:03:24 Node1 systemd[1]: Started PostgreSQL RDBMS.

Next, stop the PostgreSQL service so that Patroni can manage it:

systemctl stop postgresql

Next, you will need to create a symlinks from /usr/lib/postgresql/9.5/bin. Because, Patroni uses some tools that comes with PostgreSQL. You can create symlink with the following command:

ln -s /usr/lib/postgresql/9.5/bin/* /usr/sbin/

Install Patroni

You will need to install Patroni on Instance1 and Instance2.

Before installing Patroni, you will need to install Python and Python-pip to your server. You can install them with the following command:

apt-get install python3-pip python3-dev libpq-dev
sudo -H pip3 install --upgrade pip

Next, install Patroni using the pip command:

pip install patroni
pip install python-etcd

Install Etcd and HAProxy

Etcd is a distributed key value store that provides a reliable way to store data across a cluster of machines. Here, we will use Etcd to store the state of the Postgres cluster. So, both Postgres nodes make use of etcd to keep the Postgres cluster up and running.

You can install Etcd on Instance3 with the following command:

apt-get install etcd -y

HAProxy is free, open source software that provides a high availability load balancer and proxy server for TCP and HTTP-based applications that spreads requests across multiple servers.

Here, we will use HAProxy to forwards the connection Master or Slave node which is currently the master and online.

You can install HAProxy on Instance4 with the following command:

apt-get install haproxy -y

Configure Etcd

Etcd default configuration file is located at /etc/default directory. You will need to make some changes in etcd file.

nano /etc/default/etcd

Add the following lines:

ETCD_LISTEN_PEER_URLS="http://192.168.0.103:2380,http://127.0.0.1:7001"
ETCD_LISTEN_CLIENT_URLS="http://127.0.0.1:2379, http://192.168.0.103:2379"
ETCD_INITIAL_ADVERTISE_PEER_URLS="http://192.168.0.103:2380"
ETCD_INITIAL_CLUSTER="etcd0=http://192.168.0.103:2380,"
ETCD_ADVERTISE_CLIENT_URLS="http://192.168.0.103:2379"
ETCD_INITIAL_CLUSTER_TOKEN="cluster1"
ETCD_INITIAL_CLUSTER_STATE="new"

Save and close the file, then restart Etcd service with the following command:

systemctl restart etcd

You can now check the status of Etcd with the following command:

systemctl status etcd

Output:

● etcd.service - etcd - highly-available key value store
   Loaded: loaded (/lib/systemd/system/etcd.service; enabled; vendor preset: enabled)
   Active: active (running) since Fri 2018-09-21 22:27:47 IST; 5s ago
     Docs: https://github.com/coreos/etcd
           man:etcd
 Main PID: 4504 (etcd)
   CGroup: /system.slice/etcd.service
           └─4504 /usr/bin/etcd

Sep 21 22:27:47 Node2 etcd[4504]: starting server... [version: 2.2.5, cluster version: to_be_decided]
Sep 21 22:27:47 Node2 systemd[1]: Started etcd - highly-available key value store.
Sep 21 22:27:47 Node2 etcd[4504]: added local member ce2a822cea30bfca [http://localhost:2380 http://localhost:7001] to cluster 7e27652122e8b2ae
Sep 21 22:27:47 Node2 etcd[4504]: set the initial cluster version to 2.2
Sep 21 22:27:48 Node2 etcd[4504]: ce2a822cea30bfca is starting a new election at term 5
Sep 21 22:27:48 Node2 etcd[4504]: ce2a822cea30bfca became candidate at term 6
Sep 21 22:27:48 Node2 etcd[4504]: ce2a822cea30bfca received vote from ce2a822cea30bfca at term 6
Sep 21 22:27:48 Node2 etcd[4504]: ce2a822cea30bfca became leader at term 6
Sep 21 22:27:48 Node2 etcd[4504]: raft.node: ce2a822cea30bfca elected leader ce2a822cea30bfca at term 6
Sep 21 22:27:48 Node2 etcd[4504]: published {Name:hostname ClientURLs:[http://192.168.0.103:2379]} to cluster 7e27652122e8b2ae

Configure Patroni

Patroni uses YAML to store their configuration. So, you will need to create a configuration file for Patroni on Instance1 and Instance2:

nano /etc/patroni.yml

Add the following lines:

scope: postgres
namespace: /db/
name: postgresql0

restapi:
    listen: 192.168.0.105:8008
    connect_address: 192.168.0.105:8008

etcd:
    host: 192.168.0.103:2379

bootstrap:
    dcs:
        ttl: 30
        loop_wait: 10
        retry_timeout: 10
        maximum_lag_on_failover: 1048576
        postgresql:
            use_pg_rewind: true

    initdb:
    - encoding: UTF8
    - data-checksums

    pg_hba:
    - host replication replicator 127.0.0.1/32 md5
    - host replication replicator 192.168.0.105/0 md5
    - host replication replicator 192.168.0.104/0 md5
    - host all all 0.0.0.0/0 md5

    users:
        admin:
            password: admin
            options:
                - createrole
                - createdb

postgresql:
    listen: 192.168.0.105:5432
    connect_address: 192.168.0.105:5432
    data_dir: /data/patroni
    pgpass: /tmp/pgpass
    authentication:
        replication:
            username: replicator
            password: password
        superuser:
            username: postgres
            password: password
    parameters:
        unix_socket_directories: '.'

tags:
    nofailover: false
    noloadbalance: false
    clonefrom: false
    nosync: false

Save and close the file, when you are finished.

Next, create a data directory for Patroni on Instance1 and Instance2:

mkdir -p /data/patroni

Next, change the ownership and permissions of the data directory:

chown postgres:postgres /data/patroni
chmod 700 /data/patroni

Next, you will need to create a startup script for Patroni to manage and monitor Patroni. You can do this with the following command:

nano /etc/systemd/system/patroni.service

Add the following lines:

[Unit]
Description=Runners to orchestrate a high-availability PostgreSQL
After=syslog.target network.target

[Service]
Type=simple

User=postgres
Group=postgres

ExecStart=/usr/local/bin/patroni /etc/patroni.yml

KillMode=process

TimeoutSec=30

Restart=no

[Install]
WantedBy=multi-user.targ

Save and close the file. Then start PostgreSQL and Patroni service on both Instance1 and Instance2 with the following command:

systemctl start patroni
systemctl start postgresql

Next, check the status of Patroni using the following command:

systemctl status patroni

Output:

● patroni.service - Runners to orchestrate a high-availability PostgreSQL
   Loaded: loaded (/etc/systemd/system/patroni.service; disabled; vendor preset: enabled)
   Active: active (running) since Fri 2018-09-21 22:22:22 IST; 3min 17s ago
 Main PID: 3286 (patroni)
   CGroup: /system.slice/patroni.service
           ├─3286 /usr/bin/python3 /usr/local/bin/patroni /etc/patroni.yml
           ├─3305 postgres -D /data/patroni --config-file=/data/patroni/postgresql.conf --max_worker_processes=8 --max_locks_per_transaction=64
           ├─3308 postgres: postgres: checkpointer process                                                                                     
           ├─3309 postgres: postgres: writer process                                                                                           
           ├─3310 postgres: postgres: stats collector process                                                                                  
           ├─3315 postgres: postgres: postgres postgres 192.168.0.105(54472) idle                                                              
           ├─3320 postgres: postgres: wal writer process                                                                                       
           └─3321 postgres: postgres: autovacuum launcher process                                                                              

Sep 21 22:24:52 Node1 patroni[3286]: 2018-09-21 22:24:52,329 INFO: Lock owner: postgresql0; I am postgresql0
Sep 21 22:24:52 Node1 patroni[3286]: 2018-09-21 22:24:52,391 INFO: no action.  i am the leader with the lock

Note: Repeat all the above steps on both Instance1 and Instance2.

Configure HAProxy

PostgreSQL cluster is now up and running. It's time to configure HAProxy to forward connection receive from PostgreSQL client to the Master node.

You can configure HAProxy by editing /etc/haproxy/haproxy.cfg file:

nano /etc/haproxy/haproxy.cfg

Add the following lines:

global
    maxconn 100

defaults
    log global
    mode tcp
    retries 2
    timeout client 30m
    timeout connect 4s
    timeout server 30m
    timeout check 5s

listen stats
    mode http
    bind *:7000
    stats enable
    stats uri /

listen postgres
    bind *:5000
    option httpchk
    http-check expect status 200
    default-server inter 3s fall 3 rise 2 on-marked-down shutdown-sessions
    server postgresql_192.168.0.105_5432 192.0.2.11:5432 maxconn 100 check port 8008
    server postgresql_192.168.0.104_5432 192.0.2.12:5432 maxconn 100 check port 8008

Save and close the file. Then, restart HAProxy with the following command:

systemctl restart haproxy

Test PostgreSQL Cluster

Now, open your web browser and type the URL http://192.168.0.102:7000 (HAProxy Instance4 IP address). You will be redirected to the HAProxy dashboard as shown below:

1

In the above image, the postgresql_192.168.0.105_5432 row is highlighted in green. That means 192.168.0.105 is currently acting as the master.

If you shut down the primary node (Instance1), 192.168.0.104 (Instance2) should be acting as the master.

When you restart the Instance1, it will rejoin the cluster as a slave and sync up with the master.

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