HTTP 497 – HTTP Request Sent To HTTPS Port
(NGINX) A plain HTTP request was sent to a port that only accepts HTTPS (TLS) connections.
Common use case
A very common real-world case: an old link, bookmark, or misconfigured client hardcodes http:// against a port that only speaks TLS, e.g. 443.
History
An NGINX-specific extension that lets NGINX detect this specific mistake and respond with a helpful plain-text message instead of a raw TLS handshake failure.
Did you know?
NGINX is unusually clever here - it can peek at the start of the raw bytes, recognise plaintext HTTP instead of a TLS handshake, and reply with a readable error instead of just dropping the connection.