HTTP 503 Service Unavailable

What it means

503 Service Unavailable means the server is temporarily unable to handle the request, usually because it is overloaded or down for maintenance. It is meant to be temporary, and the server may say when to retry.

Applies to: All browsers, nginx, Apache, IIS, WordPress, AWS ALB

How to fix HTTP 503 Service Unavailable

1. Wait a few minutes and reload; check the site's status page or social accounts for maintenance notices
2. Avoid rapid refreshing, which adds load to an already struggling server
3. Check the 'Retry-After' response header for when to retry
4. If you own the site: check whether maintenance mode is still active (WordPress leaves a '.maintenance' file in the site root after a failed update)
5. If you own the site: look at CPU, memory and worker/connection limits; scale up or add caching if you are hitting capacity
6. If you own the site: check health checks on the load balancer; if all targets are unhealthy it returns 503
7. If you own the site: during planned maintenance, return 503 with Retry-After so search engines do not drop pages

Why it happens

RFC 9110 defines 503 for temporary overload or scheduled maintenance. Exhausted worker pools, all backends failing health checks, hosting resource limits and leftover maintenance flags are common causes.

FAQ

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