Critical bug slipped through to production.Root cause in test coverage found.

PM assigned in 10 minutes. Engineer starts diagnosis within the hour using your error monitoring and reproduction steps. Production bugs affecting hundreds of users are almost always: an edge case in user data that testing did not cover (the bug only surfaces for users with a specific combination of account settings), a race condition revealed at production scale (two concurrent requests interact in a way that never happens during testing), or an environment-specific issue (a production configuration not replicated in staging). The engineer traces the exact failure pattern, implements the fix, writes a regression test covering the failing case, and deploys through your standard pipeline. Users are unblocked within the session.

Yes. Regression test is a non-negotiable deliverable for every production bug fix. The test is written first before the fix is implemented to confirm it correctly fails against the buggy code and passes once the fix is applied. This is the test-driven approach for bug fixes and it prevents adding a test too broad to catch a regression of the specific bug. The test is added to your existing test suite at the appropriate level: a unit test if the bug is in a specific function, an integration test if it involves multiple modules, or an E2E test if it manifests in the full user flow. The test runs in CI on every push so the specific bug cannot be reintroduced by a future change without failing the build.

Yes. Intermittent bugs are caused by a specific class of issues with identifiable patterns: race conditions (two operations running in unpredictable order), randomness-dependent logic (code behaving differently based on non-deterministic scheduling), stale cache or state from a previous operation bleeding into the current one, floating point precision differences across environments, or dependency on external service response time that is sometimes slow enough to trigger a timeout path. The engineer adds detailed logging to the failure path and lets the system run under controlled conditions until the bug triggers, then reads the log to identify the exact failure sequence. Intermittent bugs take longer to diagnose than consistent bugs but are reliably fixable once the exact trigger is identified.

PM manages the deployment strategy to minimise risk. For high-traffic production systems: the engineer implements the fix in a feature branch, tests against staging, and deploys using blue-green deployment (spin up the new version alongside the old, switch a percentage of traffic, monitor, then switch fully zero-downtime for most failure modes), canary deployment (route 5-10% of traffic to the new version, monitor error rates for 15 minutes, then roll out fully catches regressions before they affect all users), or rolling deployment (update instances one at a time with health checks the Kubernetes default). PM advises on which strategy fits your specific infrastructure and the risk profile of this particular fix.

For critical production bugs requiring immediate resolution, the engineer uses a targeted hotfix approach. The hotfix process: create a hotfix branch from the production tag (not main, which may have unreleased changes), implement only the specific fix with no other changes, run the targeted test suite covering the affected feature area rather than the full suite to save time, deploy directly from the hotfix branch using your existing CI/CD pipeline with standard safeguards, then back-merge into main so the fix is not lost in future releases. The entire cycle from branch creation to production deployment is typically 45-90 minutes for a well-understood bug. PM documents the hotfix in your change log and incident tracker.

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