uid | title |
---|---|
coordinated-shutdown |
Coordinated Shutdown |
There's an ActorSystem
extension called CoordinatedShutdown
that will stop certain Akka.NET actors / services and execute tasks in a programmable order during shutdown.
The default phases and their orderings are defined in the default HOCON configuration as akka.coordinated-shutdown.phases
, and they are defined below:
[!code-hoconPigeon.conf]
As an end-user, you can register tasks to execute during any of these shutdown phases and add additional phases if you wish.
More phases can be added to an application by overriding the HOCON of an existing phase to include additional members in its phase.depends-on
property. Here's an example where an additional phase might be executing before shutting down the cluster, for instance:
akka.coordinated-shutdown.phases.before-cluster-shutdown.depends-on = [service-stop, my-phase]
my-phase{
timeout = 10s
recover = on
}
For each phase, the following properties can be set:
depends-on
- specifies which other phases have to run successfully first before this phase can begin;timeout
- specifies how long the tasks in this phase are allowed to run before timing out;recover
- if set tooff
, if any of the tasks in this phase throw an exception then theCoordinatedShutdown
will be aborted and no further phases will be run. If set toon
then any thrown errors are suppressed and the system will continue to execute theCoordinatedShutdown
.
The default phases are defined in a linear order, but in practice the phases are ordered into a directed acyclic graph (DAG) using Topological sort.
For instance, if you're using Akka.Cluster it's commonplace to register application-specific cleanup tasks during the cluster-leave
and cluster-exiting
phases. Here's an example:
var coordShutdown = CoordinatedShutdown.Get(myActorSystem);
coordShutdown.AddTask(CoordinatedShutdown.PhaseClusterLeave, "cleanup-my-api", () =>
{
return _myCustomSocketApi.CloseAsync().ContinueWith(tr => Done.Instance);
});
Each shutdown task added to a phase must specify a function that returns a value of type Task<Done>
. This function will be invoked once the CoordinatedShutdown.Run()
command is executed and the Task<Done>
returned by the function will be completed in parallel with all other tasks executing in the given phase. Those tasks may complete in any possible order; CoordinatedShutdown
doesn't attempt to order the execution of tasks within a single phase. Once all of those tasks have completed OR if the phases timeout has expired, the next phase will begin.
Tasks should be registered as early as possible, preferably at system startup, in order to ensure that all registered tasks are run. If tasks are added after the CoordinatedShutdown
have begun its run, it's possible that the newly registered tasks will not be executed.
There are a few different ways to start the CoordinatedShutdown
process.
If you wish to execute the CoordinatedShutdown
yourself, you can simply call CoordinatedShutdown.Run(CoordinatedShutdown.Reason)
, which takes a CoordinatedShutdown.Reason
argument will return a Task<Done>
.
[!code-csharpCoordinatedShutdownSpecs.cs]
It's safe to call this method multiple times as the shutdown process will only be run once and will return the same completion task each time. The Task<Done>
will complete once all phases have run successfully, or a phase with recover = off
failed.
Note
It's possible to subclass the CoordinatedShutdown.Reason
type and pass in a custom implementation which includes custom properties and data. This data is accessible inside the shutdown phases themselves via the CoordinatedShutdown.ShutdownReason
property.
By default, when the final phase of the CoordinatedShutdown
executes the calling ActorSystem
will be terminated. This behavior can be changed by setting the following HOCON value in your configuration:
akka.coordinated-shutdown.terminate-actor-system = off
If this setting is disabled (it is enabled b default), the ActorSystem
will not be terminated as the final phase of the CoordinatedShutdown
phases.
CoordinatedShutdown
phases, by default, are also executed when the ActorSystem
is terminated. You can change this behavior by disabling this HOCON value in your configuration:
akka.coordinated-shutdown.run-by-actor-system-terminate = off
Note
It is illegal to have run-by-actor-system-terminate enabled and have terminate-actor-system disabled. Having these configuration combination will raise a ConfigurationException
during ActorSystem
startup.
The CLR process will still be running, even when the ActorSystem
is terminated by the CoordinatedShutdown
. If you'd like to automatically terminate the process running your ActorSystem
, you can set the following HOCON value in your configuration:
akka.coordinated-shutdown.exit-clr = on
If this setting is enabled (it's disabled by default), you'll be able to shutdown the current running process automatically via an Environment.Exit(0)
call made during the final phase of the CoordinatedShutdown
.
If you're using Akka.Cluster, the CoordinatedShutdown
will automatically register tasks for completing the following:
- Gracefully leaving the cluster;
- Gracefully handing over / terminating ClusterSingleton and Cluster.Sharding instances; and
- Terminating the
Cluster
system itself.
By default, this graceful leave action will by triggered whenever the CoordinatedShutdown.Run(Reason)
method is called. Conversely, calling Cluster.Leave
on a cluster member will also cause the CoordinatedShutdown
to run and will terminate the ActorSystem
once the node has left the cluster.
CoordinatedShutdown.Run()
will also be executed if a node is removed via Cluster.Down
(non-graceful exit), but this can be disabled by changing the following Akka.Cluster HOCON setting:
akka.cluster.run-coordinated-shutdown-when-down = off
By default CoordinatedShutdown.Run()
will be called whenever the current process attempts to exit (using the AppDomain.ProcessExit
event hook) and this will give the ActorSystem
and the underlying clustering tools an opportunity to cleanup gracefully before the process finishes exiting.
If you wish to disable this behavior, you can pass in the following HOCON configuration value:
akka.coordinated-shutdown.run-by-clr-shutdown-hook = off