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The 14 things to be sure of

If you remember nothing else, remember these.

1	What defines microservices: independently deployable + owns its data. Without both it's a distributed monolith.
2	They solve an organisational problem. Start with a modular monolith; split when there's a proven reason.
3	Every call is now a network call — latency, partial failure and no ACID across services come with it.
4	Sync = needs an answer now · Async = can happen later. A chain of synchronous hops multiplies failure.
5	A broker buys you durability, buffering, fan-out and retry — and eventual consistency.
6	DLQ = messages that failed N times. Alert on depth, inspect, fix, replay — never purge.
7	Delivery is at-least-once. Exactly-once delivery doesn't exist; exactly-once effect is your job.
8	Retry (blip) + backoff + jitter, inside a circuit breaker (outage). Retries alone amplify an outage.
9	Timeout on every external call, shorter than the caller's. A slow dependency is worse than a dead one.
10	A timeout is ambiguous. It does not mean the work didn't happen.
11	Idempotency key: generated by the client, reused on every retry, stored with the result in durable shared storage — never in memory.
12	No 2PC. Saga = local transactions + compensating actions. Reserve stock before charging.
13	Transactional Outbox: write the event in the same transaction as the data; a publisher sends it afterwards.
14	Debugging is correlation id + distributed tracing — and the id must survive the queue hop.

Words that signal seniority

at-least-once · exactly-once effect · idempotency key · compensating action · transactional outbox · eventual consistency · backpressure · thundering herd · bulkhead · distributed monolith · temporal coupling · choreography vs orchestration