Introduction

An application migration can move the main site successfully while a background worker still calls the old API. The frontend and primary app server may already use the new service endpoint, but queued jobs, consumers, or scheduled workers continue sending requests to the previous backend because their runtime configuration was never updated.

Treat this as a worker-endpoint problem instead of a general API outage. Start by checking the exact service target used by the worker process, because migrations often update the interactive application path first while asynchronous job runners keep their own environment variables, config files, or container settings tied to legacy infrastructure.

Symptoms

  • A background worker still calls the old API after migration
  • The main app works, but jobs, async tasks, or queue consumers still fail or return old data
  • Logs show worker-originated requests targeting the previous API hostname or base URL
  • One workflow updates correctly in the UI while delayed or background processing still uses the old backend
  • Only queued tasks show migration-related errors after the cutover
  • The issue started after app migration, API replacement, or worker redeployment

Common Causes

  • Worker environment variables still reference the old API base URL
  • Queue consumers or scheduled jobs run from an older deployment with stale config
  • The main app was updated, but worker containers, supervisors, or service definitions were not
  • A helper library or per-job config still hardcodes the previous endpoint
  • Validation focused on live UI behavior rather than on asynchronous job execution
  • Multiple worker types exist, and only one of them was updated during migration

Step-by-Step Fix

  1. Reproduce the failing background task and capture the exact API hostname or endpoint it calls, because you need the real worker target before changing configuration.
  2. Compare the worker request destination with the intended post-migration API endpoint, because one leftover base URL can keep every queued job on the old backend.
  3. Check worker-specific environment variables, service files, container definitions, and queue-runner config, because asynchronous processes often load different settings than the main web app.
  4. Review whether the worker was redeployed from the latest release or is still running an older image, process definition, or host, because stale runtime state is a common cause after migration.
  5. Update the real worker endpoint configuration only after confirming the new API is reachable and supports the same job flow, because changing the target without validation can break background processing entirely.
  6. Restart or redeploy the worker path that exposed the issue and retest the same queued task, because editing config without recycling the worker will not change live job behavior.
  7. Verify job logs and API logs now show the worker reaching the intended backend, because the true fix is correct asynchronous traffic rather than one successful manual API test.
  8. Review additional workers, schedulers, and consumer groups if more than one background process exists, because migrations often fix one queue path while another still calls legacy services.
  9. Document the final worker endpoint configuration and deployment ownership after recovery, because asynchronous service paths are easy to miss during future API migrations.