Staged Rollout Crash Spike After Adding Background Sync
Version 4.2 of an Android app was staged at 5% for two days, then increased to 20%. Within six hours at 20%, crash-free sessions fell from 99.6% to 97.9%. The crash dashboard shows 1,240 crashes; 84% are on Android 12 and above, with a ForegroundServiceStartNotAllowedException whose stack points to SyncScheduler.startImmediateSync(). Version 4.2 introduced an instant-sync feature that calls startService when a photo upload finishes while the app is in the background. The same release also enabled a remote flag for a new checkout flow for 100% of users. Checkout conversion is up 1.8% and no checkout-related crashes are visible. The on-call engineer proposes a full production rollback. The release manager notes that store rollback is slow and that some users would remain on 4.2.
1. What immediate action should be taken? Compare halting the staged rollout, disabling a remote flag, and a full rollback.
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Halt the staged rollout first. Halting stops new installs and updates from receiving 4.2 while preserving the ability to resume. It is faster than a store rollback and avoids the mixed-version problem where some users remain on 4.2 anyway.
Next, disable the instant-sync remote flag, because the crash stack and Android version distribution match the background startService restriction. This is a targeted mitigation that can take effect without an app release. Verify that the flag is actually read at the call site and that the client handles a disabled flag by scheduling work through WorkManager instead of starting a service directly.
The checkout flag should be evaluated separately. It was enabled in the same release, but there is no evidence linking it to the crash. Disabling it would give up a measured 1.8% conversion lift without cause. Keep it enabled only if flag-change auditing confirms it is independent of the sync code path, and monitor checkout errors explicitly.
A full rollback is the wrong first move: it is slower, may not be possible for all distribution channels, and does not address users already on 4.2. Rollback is appropriate if halting and flag disable do not stop the crash growth, or if the crash affects a core workflow beyond background sync. Document the decision and the exact flag states.
2. How would you isolate the cause and confirm the mitigation before resuming the rollout?
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Use version, flag state, Android API level, and app foreground/background state as dimensions. Compare crash-free sessions for 4.2 users with instant-sync enabled against 4.2 users with it disabled, and against 4.1 users on the same Android versions. The expected pattern is a sharp drop after flag disable and no corresponding drop on 4.1. If the rate persists at the same level, the flag is not the cause or is not being honoured.
Check the exception stack for the call path and confirm whether startService is called from a background context. Reproduce on an Android 12+ emulator: start a photo upload, background the app, let the upload complete, and observe the service start behaviour. Also verify that a foreground service, if used, declares the correct type and starts while the app is visible.
Mitigation confirmation: crash-free sessions return to at least 99.5% for 4.2 users, the specific exception disappears from the dashboard, and support tickets about failed sync do not rise. Resume at 5%, not 20%, and hold for at least 48 hours or until a defined sample size is reached. Keep the instant-sync flag off until a fixed build replaces startService with WorkManager expedited work or a user-visible foreground service.
3. What changes should be made to the release process and the sync implementation before this feature ships again?
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Implementation: replace background startService with WorkManager. For time-sensitive uploads, use expedited work with a fallback to normal work; if a foreground service is genuinely required, start it only while the app is visible and declare an appropriate foreground service type with a user-visible notification. Handle the platform exception explicitly and retry through the scheduler rather than crashing.
Release process: stop bundling an unrelated monetisation flag with a risky platform behaviour change. Use separate release trains or at least separate flag owners and rollback plans. Add a staged-rollout gate: crash-free sessions must stay above 99.5% for 24 hours at 5% before increasing, and any new exception type above a threshold triggers automatic halt. Segment dashboards by Android API level, because platform restrictions concentrate there.
Testing: add instrumentation tests that background the app and complete an upload on Android 12+ and 13+. Include a device-farm matrix covering the oldest and newest supported API levels. Add a pre-release checklist item for background execution restrictions and a flag audit that records who enabled what and when. Finally, rehearse the mitigation path so halting and disabling a flag are routine, not improvised during an incident.