502 502 Bad Gateway

The server received an invalid response from an upstream server.

When you'll see it

When a proxy, load balancer or CDN got an invalid answer from the server behind it, typically because the application crashed, is restarting, or returned something malformed.

What to check

That the application process is running, and read its logs.
That the proxy points to the right host and port.
Whether it comes and goes during deploys. Health checks and rolling restarts help.
With a CDN, TLS settings between the CDN and your origin server.

Example response

HTTP/1.1 502 Bad Gateway
Server: nginx
Content-Type: text/html

SEO impact

Same as 500. It usually indicates infrastructure issues. Frequent 502s degrade crawl efficiency and risk deindexing.

At a glance

Status code	502
Group	5xx Server Errors
Class	5xx