Fix "503 Service Unavailable" errors

503 Service Unavailable errors are usually caused by slow PHP code such as slow WordPress plugins.

To resolve the problem, identify the slow app by checking each app’s PHP slow request log.

This problem can also be caused by segfaults (invalid memory access errors) in third-party PHP extensions.

Determine which app is causing the problem

To determine which of the apps on a server is responsible for the resource exhaustion that is causing the error, check the server’s app monitoring dashboards.