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HTTP Status Codes

HTTP 503 Service Unavailable

503 Service Unavailable

The server is temporarily unable to handle the request, often because it is overloaded or down for maintenance.

503 Service Unavailableruntime

Observed message

503 Service Unavailable

Why it happens

  • The service is overloaded and cannot accept more requests temporarily.
  • The application is under maintenance or intentionally unavailable.
  • An upstream dependency outage is preventing the service from functioning.

How to fix it

  1. Check service health, capacity, and maintenance state.
  2. Honor any `Retry-After` guidance if the response includes it.
  3. Restore upstream dependencies or scale the service if overload is the cause.

Official reference

MDN: 503 Service Unavailable

Related errors

500 Internal Server ErrorHTTP 500 Internal Server Error400 Bad RequestHTTP 400 Bad Request401 UnauthorizedHTTP 401 Unauthorized403 ForbiddenHTTP 403 Forbidden

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503 Service Unavailable: what it means and how to fix it | Error Atlas