Decoupling systems.
WHAT IT PROVIDES
Publishing messages to a topic, and delivering them to subscribers.
WHAT THAT ENABLES
Systems communicating without knowing about each other Absorbing bursts of load Adding consumers without changing the publisher
WHAT SUBSCRIPTION TYPES EXIST
Pull, where the subscriber requests messages Push, where messages are delivered to an endpoint
WHAT TO KNOW ABOUT DELIVERY
Messages may be delivered more than once, and may arrive out of order.
WHAT THAT REQUIRES
Processing that is safe to repeat.
HOW TO ACHIEVE THAT
Record what has been processed, and check before acting.
WHAT ORDERING KEYS PROVIDE
Ordered delivery within a key, where order matters.
WHAT TO CONFIGURE
Acknowledgement deadline, matching how long processing takes Retry behaviour A destination for messages that cannot be processed
WHY THAT LAST ONE
Otherwise a message that always fails is retried indefinitely.
WHAT TO MONITOR
Undelivered message count, which indicates consumers falling behind Failed message volume
WHAT TO ALERT ON
A backlog growing.
WHAT TO TEST
A consumer failing, and the system recovering.
