HTTP 4xx
426 Upgrade Required
The server refuses the request over the current protocol and asks the client to upgrade, for example to TLS.
What causes it
- A server requiring a newer protocol version.
How to fix it
Reconnect using the protocol named in the Upgrade header.
Example response
A typical raw HTTP response a client receives for a 426, with the headers this code is defined around.
HTTP/1.1 426 Upgrade Required
Upgrade: HTTP/2
Connection: Upgrade
Content-Type: text/html; charset=utf-8Related codes
400Common
Bad RequestThe server could not understand the request, usually because it was malformed.401Common
UnauthorizedAuthentication is required and has failed or not been provided.403Common
ForbiddenThe server understood the request but refuses to authorize it. Unlike 401, authenticating will not help.404Common
Not FoundThe server could not find the requested resource. The URL may be wrong or the resource may have been removed.405
Method Not AllowedThe HTTP method is not supported for this resource, for example a POST to a read-only endpoint.408
Request TimeoutThe server timed out waiting for the client to finish the request.Know before your visitors do.
Sentinel checks your site around the clock from multiple regions and alerts you the moment it starts returning a 4xx error, so you can fix it before it costs you.