5xx Server error
HTTP 503 Service Unavailable
The server is temporarily unable to handle the request, because it is overloaded or down for maintenance, and will likely recover. It may say when to try again in a Retry-After header.
Defined in RFC 9110, section 15.6.4(opens in a new tab)
//_01 Uptime checks
Is 503 up or down for a monitor?
Uptimecheck HTTP monitor
Default settings
Down. It is outside the default 200–399 range, so a monitor reports an outage once a second check confirms it. If 503 is the answer you expect from that URL, add it to the monitor’s expected status codes.
Is it down? checker
Free, at /is-it-down/
Down. A 5xx means the server, or something in front of it, failed to answer.
//_02 Causes and fixes
Why you see 503 and what to do
Typical causes
- Planned maintenance, including WordPress’s maintenance mode while it updates.
- More traffic than the server has workers for.
- No healthy servers left behind a load balancer.
If you run the site
- Send Retry-After during maintenance, and keep maintenance windows short.
- Find what is using up the workers or connections, and add capacity or caching.
- Mark planned work as maintenance in your monitoring, so it isn’t reported as an outage.
If you’re a visitor
- Try again in a few minutes.
Know the moment your site stops answering as it should
An Uptimecheck monitor requests your page as often as every minute, checks the status code against the ones you expect, confirms a failure with a second check and then alerts you.
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Questions
What does HTTP 503 mean?
The server is temporarily unable to handle the request, because it is overloaded or down for maintenance, and will likely recover. It may say when to try again in a Retry-After header.
Does an uptime monitor count 503 as down?
Down. It is outside the default 200–399 range, so a monitor reports an outage once a second check confirms it. If 503 is the answer you expect from that URL, add it to the monitor’s expected status codes.
Downtime is obsolete.
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