on
Called if an Exception occurred when the Delivery attempted to pick up a shard.
Please note, this callback is not invoked in case the shard cannot be picked up if it's already picked up by another worker. It is so, because such a use case is a part of normal flow, and thus does not provoke a RuntimeException.
Returns an action to take in relation to the failure.
By default this callback returns an Action that propagates the occurred exception. This means the occurred exception will be throw out of the deliverMessagesFrom() method.
Parameters
failure
contains an information about the occurred failure and gives access to predefined Actions to handle the error