405 Error - Handling CONNECT requests with GCP Load Balancer

Question

I'm having a problem getting a load balancer to forward connect requests to an instance group in GCP.

Overview:

I set up instances in an instance group which act as a proxy server. They're running and individually operational (using their own IP addresses, proxy works perfectly)

However when trying to use the instance group with a load balancer (have tried TCP, HTTP2 and HTTP) I get a 405 "The method CONNECT is inappropriate for this URL" for all of them.

Is there something I'm missing? I configured the firewall to accept all traffic (yes, I know this is dumb), set up affinity to route Client IP traffic to a known VM to keep sockets open, etc.

Thanks!

Answer 1

The load balancer is not filtering the requests before sending them to the backend, it just forwards the incoming requests to your backend services.

This response means that the method received in the request-line is known by the origin server but not supported by the target resource alerting the client that the method (verb) is not supported; this is part of an HTTP server's normal operation.1

I would suggest to check if the host url and domains are correctly defined in the web server configuration and the forwarding rule.

Also, this could be related to a misconfiguration of web servers or software components that are supposed to perform the respective action for the desired URL resource. This response may occur with the POST method, which is required for entering data and is blocked for security reasons when accessing HTML documents. Maybe enforcing the method in your service will solve this issue.

To further investigate this issue you will need to provide the more log information. I suppose you discovered these information messages from Stackdriver logging.

---