Main pg_autoctl commands

pg_auto_failover includes the command line tool pg_autoctl that implements many commands to manage your Postgres nodes. To implement the Postgres architectures described in this documentation, and more, it is generally possible to use only some of the many pg_autoctl commands.

This section of the documentation is a short introduction to the main commands that are useful when getting started with pg_auto_failover. More commands are available and help deal with a variety of situations, see the pg_autoctl commands reference for the whole list.

To understand which replication settings to use in your case, see Architecture Basics section and then the Multi-node Architectures section.

To follow a step by step guide that you can reproduce on your own Azure subscription and create a production Postgres setup from VMs, see the pg_auto_failover Tutorial section.

To understand how to setup pg_auto_failover in a way that is compliant with your internal security guide lines, read the Security settings for pg_auto_failover section.

Command line environment, configuration files, etc

As a command line tool pg_autoctl depends on some environment variables. Mostly, the tool re-uses the Postgres environment variables that you might already know.

To manage a Postgres node pg_auto_failover needs to know its data directory location on-disk. For that, some users will find it easier to export the PGDATA variable in their environment. The alternative consists of always using the --pgdata option that is available to all the pg_autoctl commands.

Creating Postgres Nodes

To get started with the simplest Postgres failover setup, 3 nodes are needed: the pg_auto_failover monitor, and 2 Postgres nodes that will get assigned roles by the monitor. One Postgres node will be assigned the primary role, the other one will get assigned the secondary role.

To create the monitor use the command:

$ pg_autoctl create monitor

The create the Postgres nodes use the following command on each node you want to create:

$ pg_autoctl create postgres

While those create commands initialize your nodes, now you have to actually run the Postgres service that are expected to be running. For that you can manually run the following command on every node:

$ pg_autoctl run

It is also possible (and recommended) to integrate the pg_auto_failover service in your usual service management facility. When using systemd the following commands can be used to produce the unit file configuration required:

$ pg_autoctl show systemd
INFO  HINT: to complete a systemd integration, run the following commands:
INFO  pg_autoctl -q show systemd --pgdata "/tmp/pgaf/m" | sudo tee /etc/systemd/system/pgautofailover.service
INFO  sudo systemctl daemon-reload
INFO  sudo systemctl enable pgautofailover
INFO  sudo systemctl start pgautofailover
[Unit]
...

While it is expected that for a production deployment each node actually is a separate machine (virtual or physical, or even a container), it is also possible to run several Postgres nodes all on the same machine for testing or development purposes.

Tip

When running several pg_autoctl nodes on the same machine for testing or contributing to pg_auto_failover, each Postgres instance needs to run on its own port, and with its own data directory. It can make things easier to then set the environement variables PGDATA and PGPORT in each terminal, shell, or tab where each instance is started.

Inspecting nodes

Once your Postgres nodes have been created, and once each pg_autoctl service is running, it is possible to inspect the current state of the formation with the following command:

$ pg_autoctl show state

To analyze what’s been happening to get to the current state, it is possible to review the past events generated by the pg_auto_failover monitor with the following command:

$ pg_autoctl show events

Hint

The pg_autoctl show commands can be run from any node in your system. Those command need to connect to the monitor and print the current state or the current known list of events as per the monitor view of the system.

Use pg_autoctl show state --local to have a view of the local state of a given node without connecting to the monitor Postgres instance.

The option --json is available in most pg_autoctl commands and switches the output format from a human readable table form to a program friendly JSON pretty-printed output.

Inspecting and Editing Replication Settings

When creating a node it is possible to use the --candidate-priority and the --replication-quorum options to set the replication properties as required by your choice of Postgres architecture.

To review the current replication settings of a formation, use the following command:

$ pg_autoctl get formation settings

It is also possible to edit those replication settings at any time while your nodes are in production: you can change your mind or adjust to new elements without having to re-deploy everything. Just use the following commands to adjust the replication settings on the fly:

$ pg_autoctl set formation number-sync-standbys
$ pg_autoctl set node replication-quorum
$ pg_autoctl set node candidate-priority

Important

The pg_autoctl get and pg_autoctl set commands always connect to the monitor Postgres instance.

The pg_autoctl set command then changes the replication settings on the node registration on the monitor. Then the monitor assigns the APPLY_SETTINGS state to the current primary node in the system for it to apply the new replication settings to its Postgres streaming replication setup.

As a result, the pg_autoctl set commands requires a stable state in the system to be allowed to proceed. Namely, the current primary node in the system must have both its Current State and its Assigned State set to primary, as per the pg_autoctl show state output.

Implementing Maintenance Operations

When a Postgres node must be taken offline for a maintenance operation, such as e.g. a kernel security upgrade or a minor Postgres update, it is best to make it so that the pg_auto_failover monitor knows about it.

  • For one thing, a node that is known to be in maintenance does not participate in failovers. If you are running with two Postgres nodes, then failover operations are entirely prevented while the standby node is in maintenance.
  • Moreover, depending on your replication settings, enabling maintenance on your standby ensures that the primary node switches to async replication before Postgres is shut down on the secondary, avoiding write queries to be blocked.

To implement maintenance operations, use the following commands:

$ pg_autoctl enable maintenance
$ pg_autoctl disable maintenance

The main pg_autoctl run service that is expected to be running in the background should continue to run during the whole maintenance operation. When a node is in the maintenance state, the pg_autoctl service is not controlling the Postgres service anymore.

Note that it is possible to enable maintenance on a primary Postgres node, and that operation then requires a failover to happen first. It is possible to have pg_auto_failover orchestrate that for you when using the command:

$ pg_autoctl enable maintenance --allow-failover

Important

The pg_autoctl enable and pg_autoctl disable commands requires a stable state in the system to be allowed to proceed. Namely, the current primary node in the system must have both its Current State and its Assigned State set to primary, as per the pg_autoctl show state output.

Manual failover, switchover, and promotions

In the cases when a failover is needed without having an actual node failure, the pg_auto_failover monitor can be used to orchestrate the operation. Use one of the following commands, which are synonyms in the pg_auto_failover design:

$ pg_autoctl perform failover
$ pg_autoctl perform switchover

Finally, it is also possible to “elect” a new primary node in your formation with the command:

$ pg_autoctl perform promotion

Important

The pg_autoctl perform commands requires a stable state in the system to be allowed to proceed. Namely, the current primary node in the system must have both its Current State and its Assigned State set to primary, as per the pg_autoctl show state output.

What’s next?

This section of the documentation is meant to help users get started by focusing on the main commands of the pg_autoctl tool. Each command has many options that can have very small impact, or pretty big impact in terms of security or architecture. Read the rest of the manual to understand how to best use the many pg_autoctl options to implement your specific Postgres production architecture.