497 HTTP Request Sent to HTTPS Port

nginx internal: a plain HTTP request arrived on a TLS port; the client receives 400.

497 at a glance

Code: 497
Name: HTTP Request Sent to HTTPS Port
Class: 4xx Client error
Status: Non-standard used by nginx
Documented by: nginx
Client receives: A 400 Bad Request page; 497 appears only in nginx logs and error_page.
Cacheable by default: Not applicable: this code is never sent to the client.

What 497 means

nginx uses 497 when a plain-HTTP request is sent to a port configured with listen ... ssl. The client receives 400 "The plain HTTP request was sent to HTTPS port". A common trick is error_page 497 =301 https://$host$request_uri; to redirect such requests to HTTPS on the same port.

What typically causes a 497

Typing http://example.com:443 or using http:// with a non-standard HTTPS port.
A load balancer or proxy forwarding HTTP to nginx's TLS port (e.g. ALB target group with protocol HTTP on port 443).
Health checks configured with the wrong protocol.

Fix it on the server

Point plain-HTTP listeners and health checks at the HTTP port, or redirect with error_page 497.

Fix it as a client or visitor

Use https:// for that port.

Example response

HTTP/1.1 400 Bad Request
Server: nginx
Content-Type: text/html

<center>The plain HTTP request was sent to HTTPS port</center>