Toronto SEO
All HTTP status codes
5xx Server Error
RFC 9110

503 Service Unavailable

The server is temporarily unable to handle the request (overload or maintenance).

What it means

HTTP 503 Service Unavailable indicates the server is currently unable to handle the request due to temporary overload or scheduled maintenance. The Retry-After header should indicate when to try again.

When it's used

Planned maintenance windows, traffic spikes overwhelming capacity, or graceful degradation under load.

Common causes
  • Scheduled maintenance window
  • Traffic spike beyond auto-scaling capacity
  • Database connection pool exhausted
  • Application deployment in progress
How to fix it
  • Add Retry-After header to guide clients
  • Auto-scale to handle traffic spikes
  • Schedule maintenance during low-traffic windows
  • Implement graceful degradation (read-only mode)
  • Use a static maintenance page during deployments
Example response
HTTP/1.1 503 Service Unavailable
Retry-After: 300
Content-Type: text/html
SEO impact

Preferred over 500 for planned maintenance — Googlebot respects Retry-After and will not deindex if brief.