# 503 Service Unavailable: the right way to go offline

> 503 Service Unavailable means the server is temporarily overloaded or down for maintenance; it’s the search-friendly code for planned downtime.

URL: https://yes-seo.com/http-status-codes/503

**503 Service Unavailable** means the server can’t handle the request right now because it’s overloaded or down for maintenance, and that it expects to recover. It’s the honest, search-friendly way to take a site offline briefly.

## Definition

[RFC 9110, section 15.6.4](https://www.rfc-editor.org/rfc/rfc9110#section-15.6.4) describes a temporary overload or scheduled maintenance “which will likely be alleviated after some delay.” The server may send a `Retry-After` header ([section 10.2.3](https://www.rfc-editor.org/rfc/rfc9110#section-10.2.3)) with a number of seconds or an HTTP date. The spec also notes that servers aren’t obliged to use 503 when overloaded; some simply refuse connections.

## Why 503 is the right code for maintenance

A maintenance page served with [200 OK](https://yes-seo.com/http-status-codes/200) tells crawlers that “We’ll be back soon” is your content, and it can replace your real pages in the index. A [404](https://yes-seo.com/http-status-codes/404) tells them the pages are gone. A 503 says “temporary, come back later.”

[Google’s documentation](https://developers.google.com/search/docs/crawling-indexing/http-network-errors) groups 503 with other server errors: Googlebot slows down, keeps already indexed URLs for a while, and drops URLs that keep returning errors. So 503 protects you during short outages, not long ones. Google’s guide to [reducing the crawl rate](https://developers.google.com/search/docs/crawling-indexing/reduce-crawl-rate) treats error codes as a tool for hours or a day or two. If maintenance will take longer, keep a read-only version of the site online instead.

Two details to get right:

- **Know what happens to robots.txt.** If it returns 503 too, Google treats the whole site as disallowed until it gets a normal answer. That pauses crawling during the outage, but make sure `robots.txt` answers 200 again the moment you’re back.

- **Don’t let the 503 be cached.** Send `Cache-Control: no-store` so a CDN doesn’t keep serving it after you’re back.

## Common causes of unplanned 503s

- Traffic spikes that exhaust PHP workers or app instances.

- Rate limiting that answers with 503 (Nginx `limit_req` does by default; [429](https://yes-seo.com/http-status-codes/429) is the clearer choice).

- Maintenance modes: WordPress, for example, serves a 503 “Briefly unavailable for scheduled maintenance” page while it updates.

- Load balancers with no healthy backends left.

## How to serve a proper maintenance 503

### Nginx

```
# inside the server block: touch /var/www/maintenance.on to switch on,
# delete it to switch off
if (-f /var/www/maintenance.on) { return 503; }
error_page 503 @maintenance;

location @maintenance {
    root /var/www/errors;
    rewrite ^ /maintenance.html break;
    add_header Retry-After 3600 always;
    add_header Cache-Control "no-store" always;
}
```

### Apache (.htaccess)

```
RewriteEngine On
RewriteCond %{DOCUMENT_ROOT}/maintenance.on -f
RewriteCond %{REQUEST_URI} !^/maintenance\.html$
RewriteRule ^ - [R=503,L]
ErrorDocument 503 /maintenance.html
Header always set Retry-After "3600" "expr=%{REQUEST_STATUS} == 503"
```

### PHP

```
http_response_code(503);
header('Retry-After: 3600');
header('Cache-Control: no-store');
```

## How to check

While maintenance is on, run a few URLs through the [HTTP status checker](https://yes-seo.com/http-status-checker) and confirm they return 503, not 200 or a redirect to a maintenance URL. The [HTTP header checker](https://yes-seo.com/http-header-checker) shows whether `Retry-After` and `Cache-Control` came through.

```
HTTP/1.1 503 Service Unavailable
Retry-After: 3600
Cache-Control: no-store
Content-Type: text/html; charset=utf-8
```

## Frequently asked questions

### How long can my site return 503 without losing rankings?

Keep it short. Google treats 503 as temporary, and its crawl-rate guidance talks about hours or a day or two. If URLs keep returning errors for longer, Google starts dropping them from the index.

### Does Google respect the Retry-After header?

Google doesn’t document exactly how it uses Retry-After, and Googlebot slows down on any 503 anyway. Sending it costs nothing and helps other clients and crawlers that do honor it.

### Should I redirect visitors to a maintenance page?

No. Serve the maintenance message with a 503 status at the original URLs. Redirecting to a separate maintenance URL with a 302 makes crawlers follow it to a 200 page, which defeats the purpose.