Delivery level for AWS service events
Each AWS service that generates events sends them to EventBridge as either best effort or durable delivery attempts.
Best effort delivery means that the service attempts to send all events to EventBridge, but in some rare cases an event might not be delivered.
Durable delivery means the service will successfully attempt to deliver events to EventBridge at least once.
Once a valid event is delivered to EventBridge, EventBridge matches it against rules and then follows the retry policy and any dead-letter queue specified for the event target(s). For more information, see Retrying event delivery in the EventBridge User Guide.