464 Incompatible Protocol (ALB)

AWS ALB: the request protocol is incompatible with the target group's protocol version.

464 at a glance

Code: 464
Name: Incompatible Protocol (ALB)
Class: 4xx Client error
Status: Non-standard used by AWS Application Load Balancer
Documented by: AWS Application Load Balancer
Cacheable by default: No by default. Caches only store responses with unrecognised status codes if explicit freshness (Cache-Control max-age) is given.

What 464 means

An Application Load Balancer returns 464 when the protocol of the incoming request does not match what the target group's protocol version can accept, for example an HTTP/1.1 request routed to a target group configured for gRPC or HTTP/2 only.

What typically causes a 464

HTTP/1.1 clients hitting a listener rule that forwards to a gRPC target group.
gRPC clients routed to a target group with protocol version HTTP1.

Fix it on the server

Route by path or header so gRPC and HTTP/1 traffic reach target groups with matching protocol versions.

Fix it as a client or visitor

Use the protocol the endpoint expects (HTTP/2 for gRPC).

Example response

HTTP/1.1 464
Server: awselb/2.0
Content-Type: text/html