A modular monolith needs boundaries the code can enforce
One deployable application can contain clear business modules. The separation becomes useful when callers cannot casually bypass each module's rules and data ownership.
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The database committed. Did the event leave?
A business write and a message publish can fail independently. Save the intention to publish in the same transaction as the business change, then deliver it through a recoverable worker.
Read articleA retry should not create a second business action
When a response is lost, the caller needs a way to repeat the request without repeating its effect. Give the intended action an identity that survives every attempt.
Read articleChange an API without stranding its existing clients
Compatibility includes behaviour, defaults and error handling as well as field names. Review what older callers rely on before changing the contract.
Read articleCompensation is a business action, not a database undo
A distributed workflow cannot usually erase every completed step. Define the corrective business action for each effect and make unresolved states visible.
Read articleTenant isolation must survive background work
Filtering an API request by organisation is not enough if jobs, caches or exports lose that context. Carry the boundary through every path that reads or changes tenant data.
Read articleEvents need a meaning that survives new consumers
A message can remain valid JSON while its meaning changes. Define the business fact, its timing and its replay behaviour before other systems depend on it.
Read articleA cache needs a freshness promise
Decide how old a value may be and what happens when that limit is exceeded. Faster reads are useful only while the result remains suitable for the task.
Read articleA database migration has to support two application versions
During a rolling release, old and new code share the database. Design the transition around that overlap before removing or reinterpreting stored data.
Read articleTwo valid requests can still produce an invalid result
Concurrency control protects the rule shared requests depend on. Start with that rule, then choose conditional writes, locks or transaction isolation to enforce it.
Read articleStart a module with an explicit public contract
Define the operation other features need, then hide the rules and persistence behind it. This gives the module a boundary that can survive internal changes.
Read articleWrite the event intention with the business change
Keep the order update and outbox insert in one transaction. Then give the publisher stable event identities and a clear recovery path for uncertain delivery.
Read articleBind the retry key to the original request
Store the key, account scope and material payload together before executing. Matching retries can reuse the outcome, while conflicting reuse receives an explicit error.
Read articleAdd the new field before requiring it
Introduce a field in stages so older callers remain valid while newer ones adopt it. Define omission and conflict behaviour before changing validation.
Read articleMap each committed effect before defining its compensation
Design the recovery record from the actual side effects. A list of service calls does not tell the coordinator what can safely be corrected after failure.
Read articleCarry tenant identity into queued work
A worker needs an explicit, trusted scope for the job it executes. Save that scope at submission and validate it again according to the workflow's authority policy.
Read articleDefine whether the event is a snapshot or a change
Build an event contract around one interpretation. A consumer needs to know whether it should replace a view, apply a transition or fetch more information.
Read articleMake cache keys describe the result they contain
Include every input that changes a cached response. A resource identifier alone is rarely enough for tenant data, translations or filtered views.
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