413 Request Entity Too Large (nginx client_max_body_size)

What’s actually happening

An upload or a large form POST fails with a 413 page rendered by nginx itself, not by your app. The backend logs show nothing because the request never reached PHP. nginx's default cap is 1 MB, so anything bigger than a small file trips it. The error.log line reports the exact byte count the client tried to send.

Common causes

• The upload is larger than client_max_body_size, which defaults to 1m if you never set it.
• The directive is set in the wrong context. A value in http {} can be overridden, or a value in the wrong server/location block does not apply to the route handling the upload.
• A long form or a base64-encoded payload in a POST body crosses the limit even without an obvious file attachment.
• An API endpoint receiving JSON or multipart data over the limit.
• client_max_body_size was raised but nginx was never reloaded, so the old value is still live.

How to fix it

1. Raise the directive in the right blockSet client_max_body_size to a real ceiling, for example client_max_body_size 50m;. Put it in the server {} block, or in the specific location {} that handles uploads, so it actually applies to that route.
2. Test the config and reloadRun nginx -t to validate, then systemctl reload nginx (or nginx -s reload). A reload is required; editing the file alone changes nothing.
3. Raise the matching PHP limitsnginx is only the first gate. If you are on PHP, set upload_max_filesize and post_max_size in php.ini to at least the same ceiling, then restart php-fpm. Otherwise you clear the 413 and hit a PHP-level rejection instead.
4. Allow unlimited only where it is safeclient_max_body_size 0; disables the check for a location. Scope it to a trusted upload endpoint only; never apply it server-wide, since it invites memory-exhaustion abuse.
5. Confirm with the byte count in the logtail the nginx error.log while you reproduce. The 'client intended to send too large body' line gives the exact size, so you can set the ceiling just above the real maximum you need to accept.