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Deploying PostgreSQL for high availability with Patroni on Debian or Ubuntu

This guide provides instructions on how to set up a highly available PostgreSQL cluster with Patroni on Debian or Ubuntu.

Preconditions

  1. This is an example deployment where etcd runs on the same host machines as the Patroni and PostgreSQL and there is a single dedicated HAProxy host. Alternatively etcd can run on different set of nodes.

    If etcd is deployed on the same host machine as Patroni and PostgreSQL, separate disk system for etcd and PostgreSQL is recommended due to performance reasons.

  2. For this setup, we will use the nodes running on Ubuntu 22.04 as the base operating system:

Node name Public IP address Internal IP address
node1 157.230.42.174 10.104.0.7
node2 68.183.177.183 10.104.0.2
node3 165.22.62.167 10.104.0.8
HAProxy-demo 134.209.111.138 10.104.0.6

!!! note

We recommend not to expose the hosts/nodes where Patroni / etcd / PostgreSQL are running to public networks due to security risks.  Use Firewalls, Virtual networks, subnets or the like to protect the database hosts from any kind of attack.

Initial setup

Configure every node.

Set up hostnames in the /etc/hosts file

It's not necessary to have name resolution, but it makes the whole setup more readable and less error prone. Here, instead of configuring a DNS, we use a local name resolution by updating the file /etc/hosts. By resolving their hostnames to their IP addresses, we make the nodes aware of each other's names and allow their seamless communication.

=== "node1"

1. Set up the hostname for the node

    ```{.bash data-prompt="$"}
    $ sudo hostnamectl set-hostname node1
    ```

2. Modify the `/etc/hosts` file to include the hostnames and IP addresses of the remaining nodes. Add the following at the end of the `/etc/hosts` file on all nodes:   

    ```text hl_lines="3 4"
    # Cluster IP and names 
    10.104.0.1 node1 
    10.104.0.2 node2 
    10.104.0.3 node3
    ```

=== "node2"

1. Set up the hostname for the node

    ```{.bash data-prompt="$"}
    $ sudo hostnamectl set-hostname node2
    ```

2. Modify the `/etc/hosts` file to include the hostnames and IP addresses of the remaining nodes. Add the following at the end of the `/etc/hosts` file on all nodes:   

    ```text hl_lines="2 4"
    # Cluster IP and names 
    10.104.0.1 node1 
    10.104.0.2 node2 
    10.104.0.3 node3
    ```

=== "node3"

1. Set up the hostname for the node

    ```{.bash data-prompt="$"}
    $ sudo hostnamectl set-hostname node3
    ```

2. Modify the `/etc/hosts` file to include the hostnames and IP addresses of the remaining nodes. Add the following at the end of the `/etc/hosts` file on all nodes:   

    ```text hl_lines="2 3"
    # Cluster IP and names 
    10.104.0.1 node1 
    10.104.0.2 node2 
    10.104.0.3 node3
    ```

=== "HAproxy-demo"

1. Set up the hostname for the node

    ```{.bash data-prompt="$"}
    $ sudo hostnamectl set-hostname HAProxy-demo
    ```

2. Modify the `/etc/hosts` file. The HAProxy instance should have the name resolution for all the three nodes in its `/etc/hosts` file. Add the following lines at the end of the file:    

    ```text hl_lines="3 4 5"
    # Cluster IP and names
    10.104.0.6 HAProxy-demo
    10.104.0.1 node1
    10.104.0.2 node2
    10.104.0.3 node3
    ```

Install the software

Run the following commands on node1, node2 and node3:

  1. Install Percona Distribution for PostgreSQL

    • Disable the upstream postgresql-{{pgversion}} package.

    • Install the percona-release repository management tool

      --8<-- "percona-release-apt.md"

    • Enable the repository

      $ sudo percona-release setup ppg{{pgversion}}

    • Install Percona Distribution for PostgreSQL package

      $ sudo apt install percona-postgresql-{{pgversion}}

  2. Install some Python and auxiliary packages to help with Patroni and etcd

    $ sudo apt install python3-pip python3-dev binutils

  3. Install etcd, Patroni, pgBackRest packages:

    $ sudo apt install percona-patroni \
etcd etcd-server etcd-client \
percona-pgbackrest

  4. Stop and disable all installed services:

    $ sudo systemctl stop {etcd,patroni,postgresql}
$ systemctl disable {etcd,patroni,postgresql}

  5. Even though Patroni can use an existing Postgres installation, remove the data directory to force it to initialize a new Postgres cluster instance.

    $ sudo systemctl stop postgresql
$ sudo rm -rf /var/lib/postgresql/{{pgversion}}/main

Configure etcd distributed store

In our implementation we use etcd distributed configuration store. Refresh your knowledge about etcd.

!!! note

If you [installed the software from tarballs](../tarball.md), you must first [enable etcd](../enable-extensions.md#etcd) before configuring it.

To get started with etcd cluster, you need to bootstrap it. This means setting up the initial configuration and starting the etcd nodes so they can form a cluster. There are the following bootstrapping mechanisms:

  • Static in the case when the IP addresses of the cluster nodes are known
  • Discovery service - for cases when the IP addresses of the cluster are not known ahead of time.

Since we know the IP addresses of the nodes, we will use the static method. For using the discovery service, please refer to the etcd documentation :octicons-external-link-16:{:target="_blank"}.

We will configure and start all etcd nodes in parallel. This can be done either by modifying each node's configuration or using the command line options. Use the method that you prefer more.

Method 1. Modify the configuration file

  1. Create the etcd configuration file on every node. You can edit the sample configuration file /etc/etcd/etcd.conf.yaml or create your own one. Replace the node names and IP addresses with the actual names and IP addresses of your nodes.

    === "node1"

      ```yaml title="/etc/etcd/etcd.conf.yaml"
  name: 'node1'
  initial-cluster-token: PostgreSQL_HA_Cluster_1
  initial-cluster-state: new
  initial-cluster: node1=http://10.104.0.1:2380,node2=http://10.104.0.2:2380,node3=http://10.104.0.3:2380
  data-dir: /var/lib/etcd
  initial-advertise-peer-urls: http://10.104.0.1:2380 
  listen-peer-urls: http://10.104.0.1:2380
  advertise-client-urls: http://10.104.0.1:2379
  listen-client-urls: http://10.104.0.1:2379
  ```

    === "node2"

      ```yaml title="/etc/etcd/etcd.conf.yaml"
  name: 'node2'
  initial-cluster-token: PostgreSQL_HA_Cluster_1
  initial-cluster-state: new
  initial-cluster: node1=http://10.104.0.1:2380,node2=http://10.104.0.2:2380,     node3=http://10.104.0.3:2380
  data-dir: /var/lib/etcd
  initial-advertise-peer-urls: http://10.104.0.2:2380 
  listen-peer-urls: http://10.104.0.2:2380
  advertise-client-urls: http://10.104.0.2:2379
  listen-client-urls: http://10.104.0.2:2379
  ```

    === "node3"

      ```yaml title="/etc/etcd/etcd.conf.yaml"
  name: 'node3'
  initial-cluster-token: PostgreSQL_HA_Cluster_1
  initial-cluster-state: new
  initial-cluster: node1=http://10.104.0.1:2380,node2=http://10.104.0.2:2380,     node3=http://10.104.0.3:2380
  data-dir: /var/lib/etcd
  initial-advertise-peer-urls: http://10.104.0.3:2380 
  listen-peer-urls: http://10.104.0.3:2380
  advertise-client-urls: http://10.104.0.3:2379
  listen-client-urls: http://10.104.0.3:2379
  ```

  2. Enable and start the etcd service on all nodes:

    $ sudo systemctl enable --now etcd
$ sudo systemctl start etcd
$ sudo systemctl status etcd

    During the node start, etcd searches for other cluster nodes defined in the configuration. If the other nodes are not yet running, the start may fail by a quorum timeout. This is expected behavior. Try starting all nodes again at the same time for the etcd cluster to be created.

--8<-- "check-etcd.md"

Method 2. Start etcd nodes with command line options

  1. On each etcd node, set the environment variables for the cluster members, the cluster token and state:

    TOKEN=PostgreSQL_HA_Cluster_1
CLUSTER_STATE=new
NAME_1=node1
NAME_2=node2
NAME_3=node3
HOST_1=10.104.0.1
HOST_2=10.104.0.2
HOST_3=10.104.0.3
CLUSTER=${NAME_1}=http://${HOST_1}:2380,${NAME_2}=http://${HOST_2}:2380,${NAME_3}=http://${HOST_3}:2380

  2. Start each etcd node in parallel using the following command:

    === "node1"

     ```{.bash data-prompt="$"}
 THIS_NAME=${NAME_1}
 THIS_IP=${HOST_1}
 etcd --data-dir=data.etcd --name ${THIS_NAME} \
 	--initial-advertise-peer-urls http://${THIS_IP}:2380 --listen-peer-urls http://${THIS_IP}:2380 \
 	--advertise-client-urls http://${THIS_IP}:2379 --listen-client-urls http://${THIS_IP}:2379 \
 	--initial-cluster ${CLUSTER} \
 	--initial-cluster-state ${CLUSTER_STATE} --initial-cluster-token ${TOKEN}
 ```

    === "node2"

     ```{.bash data-prompt="$"}
 THIS_NAME=${NAME_2}
 THIS_IP=${HOST_2}
 etcd --data-dir=data.etcd --name ${THIS_NAME} \
 	--initial-advertise-peer-urls http://${THIS_IP}:2380 --listen-peer-urls http://${THIS_IP}:2380 \
 	--advertise-client-urls http://${THIS_IP}:2379 --listen-client-urls http://${THIS_IP}:2379 \
 	--initial-cluster ${CLUSTER} \
 	--initial-cluster-state ${CLUSTER_STATE} --initial-cluster-token ${TOKEN}
 ```

    === "node3"

     ```{.bash data-prompt="$"}
 THIS_NAME=${NAME_3}
 THIS_IP=${HOST_3}
 etcd --data-dir=data.etcd --name ${THIS_NAME} \
 	--initial-advertise-peer-urls http://${THIS_IP}:2380 --listen-peer-urls http://${THIS_IP}:2380 \
 	--advertise-client-urls http://${THIS_IP}:2379 --listen-client-urls http://${THIS_IP}:2379 \
 	--initial-cluster ${CLUSTER} \
 	--initial-cluster-state ${CLUSTER_STATE} --initial-cluster-token ${TOKEN}
 ```

--8<-- "check-etcd.md"

Configure Patroni

Run the following commands on all nodes. You can do this in parallel:

  1. Export and create environment variables to simplify the config file creation:

    • Node name:

      $ export NODE_NAME=`hostname -f`

    • Node IP:

      $ export NODE_IP=`hostname -i | awk '{print $1}'`

    • Create variables to store the PATH:

      DATA_DIR="/var/lib/postgresql/{{pgversion}}/main"
PG_BIN_DIR="/usr/lib/postgresql/{{pgversion}}/bin"

      NOTE: Check the path to the data and bin folders on your operating system and change it for the variables accordingly.

    • Patroni information:

      NAMESPACE="percona_lab"
SCOPE="cluster_1"

  2. Use the following command to create the /etc/patroni/patroni.yml configuration file and add the following configuration for node1:

    echo "
namespace: ${NAMESPACE}
scope: ${SCOPE}
name: ${NODE_NAME}

restapi:
    listen: 0.0.0.0:8008
    connect_address: ${NODE_IP}:8008

etcd3:
    host: ${NODE_IP}:2379

bootstrap:
  # this section will be written into Etcd:/<namespace>/<scope>/config after initializing new cluster
  dcs:
      ttl: 30
      loop_wait: 10
      retry_timeout: 10
      maximum_lag_on_failover: 1048576

      postgresql:
          use_pg_rewind: true
          use_slots: true
          parameters:
              wal_level: replica
              hot_standby: "on"
              wal_keep_segments: 10
              max_wal_senders: 5
              max_replication_slots: 10
              wal_log_hints: "on"
              logging_collector: 'on'
              max_wal_size: '10GB'
              archive_mode: "on"
              archive_timeout: 600s
              archive_command: "cp -f %p /home/postgres/archived/%f"
      pg_hba:
      - local all all          peer
      - host replication replicator 127.0.0.1/32 trust
      - host replication replicator 192.0.0.0/8 scram-sha-256
      - host all all 0.0.0.0/0 scram-sha-256
      recovery_conf:
        restore_command: cp /home/postgres/archived/%f %p

  # some desired options for 'initdb'
  initdb: # Note: It needs to be a list (some options need values, others are switches)
      - encoding: UTF8
      - data-checksums

postgresql:
    cluster_name: cluster_1
    listen: 0.0.0.0:5432
    connect_address: ${NODE_IP}:5432
    data_dir: ${DATA_DIR}
    bin_dir: ${PG_BIN_DIR}
    pgpass: /tmp/pgpass0
    authentication:
        replication:
            username: replicator
            password: replPasswd
        superuser:
            username: postgres
            password: qaz123
    parameters:
        unix_socket_directories: "/var/run/postgresql/"
    create_replica_methods:
        - basebackup
    basebackup:
        checkpoint: 'fast'

watchdog:
  mode: required # Allowed values: off, automatic, required
  device: /dev/watchdog
  safety_margin: 5


tags:
    nofailover: false
    noloadbalance: false
    clonefrom: false
    nosync: false
" | sudo tee -a /etc/patroni/patroni.yml

    ??? admonition "Patroni configuration file"

     Let’s take a moment to understand the contents of the `patroni.yml` file. 

 The first section provides the details of the node and its connection ports. After that, we have the `etcd` service and its port details.

 Following these, there is a `bootstrap` section that contains the PostgreSQL configurations and the steps to run once the database is initialized. The `pg_hba.conf` entries specify all the other nodes that can connect to this node and their authentication mechanism.

  3. Check that the systemd unit file percona-patroni.service is created in /etc/systemd/system. If it is created, skip this step.

    If it's not created, create it manually and specify the following contents within:

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

 [Service]
 Type=simple 

 User=postgres
 Group=postgres 

 # Start the patroni process
 ExecStart=/bin/patroni /etc/patroni/patroni.yml 

 # Send HUP to reload from patroni.yml
 ExecReload=/bin/kill -s HUP $MAINPID 

 # only kill the patroni process, not its children, so it will gracefully stop postgres
 KillMode=process 

 # Give a reasonable amount of time for the server to start up/shut down
 TimeoutSec=30 

 # Do not restart the service if it crashes, we want to manually inspect database on failure
 Restart=no 

 [Install]
 WantedBy=multi-user.target

  4. Make systemd aware of the new service:

    $ sudo systemctl daemon-reload

  5. Repeat steps 1-4 on the remaining nodes. In the end you must have the configuration file and the systemd unit file created on every node.

  6. Now it's time to start Patroni. You need the following commands on all nodes but not in parallel. Start with the node1 first, wait for the service to come to live, and then proceed with the other nodes one-by-one, always waiting for them to sync with the primary node:

    $ sudo systemctl enable --now patroni
$ sudo systemctl restart patroni

    When Patroni starts, it initializes PostgreSQL (because the service is not currently running and the data directory is empty) following the directives in the bootstrap section of the configuration file.

  7. Check the service to see if there are errors:

    $ sudo journalctl -fu patroni

    A common error is Patroni complaining about the lack of proper entries in the pg_hba.conf file. If you see such errors, you must manually add or fix the entries in that file and then restart the service.

    Changing the patroni.yml file and restarting the service will not have any effect here because the bootstrap section specifies the configuration to apply when PostgreSQL is first started in the node. It will not repeat the process even if the Patroni configuration file is modified and the service is restarted.

  8. Check the cluster. Run the following command on any node:

    $ patronictl -c /etc/patroni/patroni.yml list $SCOPE

    The output resembles the following:

    + Cluster: cluster_1 (7440127629342136675) -----+----+-------+
| Member | Host       | Role    | State     | TL | Lag in MB |
+--------+------------+---------+-----------+----+-----------+
| node1  | 10.0.100.1 | Leader  | running   |  1 |           |
| node2  | 10.0.100.2 | Replica | streaming |  1 |         0 |
| node3  | 10.0.100.3 | Replica | streaming |  1 |         0 |
+--------+------------+---------+-----------+----+-----------+

If Patroni has started properly, you should be able to locally connect to a PostgreSQL node using the following command:

$ sudo psql -U postgres

The command output is the following:

psql ({{dockertag}})
Type "help" for help.

postgres=#

Configure HAProxy

HAproxy is the load balancer and the single point of entry to your PostgreSQL cluster for client applications. A client application accesses the HAPpoxy URL and sends its read/write requests there. Behind-the-scene, HAProxy routes write requests to the primary node and read requests - to the secondaries in a round-robin fashion so that no secondary instance is unnecessarily loaded. To make this happen, provide different ports in the HAProxy configuration file. In this deployment, writes are routed to port 5000 and reads - to port 5001

This way, a client application doesn’t know what node in the underlying cluster is the current primary. HAProxy sends connections to a healthy node (as long as there is at least one healthy node available) and ensures that client application requests are never rejected.

  1. Install HAProxy on the HAProxy-demo node:

    $ sudo apt install percona-haproxy

  2. The HAProxy configuration file path is: /etc/haproxy/haproxy.cfg. Specify the following configuration in this file.

    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 primary
    bind *:5000
    option httpchk /primary 
    http-check expect status 200
    default-server inter 3s fall 3 rise 2 on-marked-down shutdown-sessions
    server node1 node1:5432 maxconn 100 check port 8008
    server node2 node2:5432 maxconn 100 check port 8008
    server node3 node3:5432 maxconn 100 check port 8008

listen standbys
    balance roundrobin
    bind *:5001
    option httpchk /replica 
    http-check expect status 200
    default-server inter 3s fall 3 rise 2 on-marked-down shutdown-sessions
    server node1 node1:5432 maxconn 100 check port 8008
    server node2 node2:5432 maxconn 100 check port 8008
    server node3 node3:5432 maxconn 100 check port 8008

    HAProxy will use the REST APIs hosted by Patroni to check the health status of each PostgreSQL node and route the requests appropriately.

  3. Restart HAProxy:

    $ sudo systemctl restart haproxy

  4. Check the HAProxy logs to see if there are any errors:

    $ sudo journalctl -u haproxy.service -n 100 -f

Next steps

Configure pgBackRest{.md-button}