464 Incompatible protocol
HTTP response status code 464 Incompatible protocol is an unofficial client error specific to AWS Elastic Load Balancer and used to indicate that the load balancer received an incompatible HTTP request protocol.
When the 464 Incompatible protocol HTTP status code is received, the client has submitted a HTTP request that is incompatible with the version configuration of the target group protocol. For example, when the request protocol is HTTP/1.1 but the target group protocol is HTTP/2.
Search engines like Google will not index a URL with 464 HTTP response status code, and consequently, URLs that have been indexed in the past but are now returning this HTTP status code will be removed from the search results.
In the example, the HTTP client requests a resource using the HTTP/1.1 protocol. The server responds with the 464 Incompatible protocol status code to indicate that this protocol is not supported by the target group.
GET /tech-news HTTP/1.1 Host: www.example.ai
HTTP/1.1 464 Content-Type: text/html Content-Length: 147 <html> <head> <title>AWS Load Balancer Error</title> </head> <body> <p>Incompatible protocol. Please use HTTP/2.</p> </body> </html>
The 464 Incompatible protocol status code is a client error that is sent by AWS Elastic Load Balancer when the HTTP client uses a protocol that is not supported by the target group.