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events.md

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Events

The BBS emits events when a DesiredLRP or ActualLRP is created, updated, or deleted. The following sections provide details on how to subscribe to those events as well as the type of events supported by the BBS.

Subscribing to events

You can use the SubscribeToEvents(logger lager.Logger) (events.EventSource, error) client method to subscribe to events. For example:

client := bbs.NewClient(url)
eventSource, err := client.SubscribeToEvents(logger)
if err != nil {
    log.Printf("failed to subscribe to events: " + err.Error())
}

You can then loop through the events by calling Next in a loop, for example:

event, err := eventSource.Next()
if err != nil {
    log.Printf("failed to get next event: " + err.Error())
}
log.Printf("received event: %#v", event)

To access the event field values, you must convert the event to the right type. You can use the EventType method to determine the type of the event, for example:

if event.EventType() == models.EventTypeActualLRPCrashed {
  crashEvent := event.(*models.ActualLRPCrashedEvent)
  log.Printf("lrp has crashed. err: %s", crashEvent.CrashReason)
}

The following types of events are emitted:

DesiredLRP events

DesiredLRPCreatedEvent

When a new DesiredLRP is created, a DesiredLRPCreatedEvent is emitted. The value of the DesiredLrp field contains information about the DesiredLRP that was just created.

DesiredLRPChangedEvent

When a DesiredLRP changes, a DesiredLRPChangedEvent is emitted. The value of the Before and After fields have information about the DesiredLRP before and after the change.

DesiredLRPRemovedEvent

When a DesiredLRP is deleted, a DesiredLRPRemovedEvent is emitted. The field value of DesiredLrp will have information about the DesiredLRP that was just removed.

ActualLRP events

ActualLRPCreatedEvent

When a new ActualLRP is created, a ActualLRPCreatedEvent is emitted. The value of the ActualLrpGroup field contains more information about the ActualLRP.

ActualLRPChangedEvent

When a ActualLRP changes, a ActualLRPChangedEvent is emitted. The value of the Before and After fields contains information about the ActualLRP state before and after the change.

ActualLRPRemovedEvent

When a ActualLRP is removed, a ActualLRPRemovedEvent is emitted. The value of the ActualLrp field contains information about the ActualLRP that was just removed.

ActualLRPCrashedEvent

When a ActualLRP crashes a ActualLRPCrashedEvent is emitted. The event will have the following field values:

  1. ActualLRPKey: The LRP key of the ActualLRP.
  2. ActualLRPInstanceKey: The instance key of the ActualLRP.
  3. CrashCount: The number of times the ActualLRP has crashed, including this latest crash.
  4. CrashReason: The last error that caused the ActualLRP to crash.
  5. Since: The timestamp when the ActualLRP last crashed, in nanoseconds in the Unix epoch.