Each Deployment in Application Manager has an Event log attached to it. The Event log reports the state of operations such as state transitions that are executed asynchronously.
A Flink job can switch to an erroneous state at any time, requiring a state transition back to the desired state. Those errors and subsequent transitions are also reported in the Event log.
The Event log exposes events both in a human readable way and with a machine-readable unique identifier as part of the Event metadata.