View Source Oban.Peer behaviour (Oban v2.13.4)

The Peer module maintains leadership for a particular Oban instance within a cluster.

Leadership is used by plugins, primarily, to prevent duplicate work accross nodes. For example, only the leader's Cron plugin will insert new jobs. You can use peer leadership to extend Oban with custom plugins, or even within your own application.

Note a few important details about how peer leadership operates:

  • Each peer checks for leadership at a 30 second interval. When the leader exits it broadcasts a message to all other peers to encourage another one to assume leadership.

  • Each Oban instances supervises a distinct Oban.Peer instance. That means that with multiple Oban instances on the same node one instance may be the leader, while the others aren't.

  • Without leadership, global plugins (Cron, Lifeline, Stager, etc.), will not run on any node.

available-peer-implementations

Available Peer Implementations

There are two built-in peering modules:

  • Oban.Peers.Postgres — uses table-based leadership through the oban_peers table and works in any environment, with or without clustering. This is the default.

  • Oban.Peers.Global — coordinates global locks through distributed Erlang, requires distributed Erlang.

examples

Examples

Check leadership for the default Oban instance:

Oban.Peer.leader?()
# => true

That is identical to using the name Oban:

Oban.Peer.leader?(Oban)
# => true

Check leadership for a couple of instances:

Oban.Peer.leader?(Oban.A)
# => true

Oban.Peer.leader?(Oban.B)
# => false

Link to this section Summary

Callbacks

Check whether the current peer instance leads the cluster.

Starts a peer instance.

Functions

Check whether the current instance leads the cluster.

Link to this section Types

@type option() ::
  {:name, module()} | {:conf, Oban.Config.t()} | {:interval, timeout()}

Link to this section Callbacks

@callback leader?(pid()) :: boolean()

Check whether the current peer instance leads the cluster.

@callback start_link([option()]) :: GenServer.on_start()

Starts a peer instance.

Link to this section Functions

Link to this function

leader?(conf_or_name \\ Oban, timeout \\ 5000)

View Source

Check whether the current instance leads the cluster.

example

Example

Check leadership for the default Oban instance:

Oban.Peer.leader?()
# => true

Check leadership for an alternate instance named Oban.Private:

Oban.Peer.leader?(Oban.Private)
# => true