Error "Bad gRPC response. HTTP status code: 500" when set $var in NGINX grpc_pass

[Kotnstantin]

When i set $var in grpc_pass i can't connect grpc-client to server, I get the FAIL error

[Microsoft.Extensions.Hosting.Internal.Host) [BackgroundServiceFaulted status BackgroundServledGrpc.Co.RpcException (StatusCode="Unknown", Detail="Bad gRPC response. HTTP status code: 500")

The purpose of setting a variable is to bypass the situation where one of the services that proxies NGINX crashes, and when NGINX restarts, the other services continue to work. With proxy_pass directive all works and tests are successful, with grpc_pass - no

    location / {
        resolver 127.0.0.11 valid=30s;
        set $webuidev https://dev_webuidev;
        proxy_pass $webuidev;

        #proxy_pass https://dev_webuidev;
        # Configuration for WebSockets
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection $connection_upgrade;
        proxy_cache off;
        # WebSockets were implemented after http/1.0
        proxy_http_version 1.1;
        # Configuration for ServerSentEvents
        proxy_buffering off;
        proxy_set_header Host $host;
        proxy_cache_bypass $http_upgrade;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;   
        proxy_set_header X-Forwarded-Proto $scheme;
        proxy_set_header X-URL-SCHEME https;
    }
    location /App.Room.Api.Contract.ApiService/UpdateOpcDaTags {
        resolver 127.0.0.11 valid=30s;
        set $grpc_webuidev grpcs://dev_webuidev;
        grpc_pass $grpc_webuidev;

        #grpc_pass grpcs://dev_webuidev;
    }

[Kotnstantin]

After a long review of the materials and tests, the error was discovered.

If we are using variables in the configuration, grpc_pass should have a port on which this grpc can be listened, in this example https and grpcs will use port 443.

So the working configuration for me is:

    server {
        listen 443 http2:
        server _name opc.org.com;
        ssl....;
        location / {
            resolver 127.0.0.11 valid=30s;
            set $https_webui https://dev_webui;
            proxy_pass $https_webui;
        }  
        location /App.Room.Api.Contract.ApiService/UpdateOpcDaTags {
            resolver 127.0.0.11 valid=30s;
            set $grpc_webui grpcs://dev_webui:443;
            grpc_pass $grpc_webui;
        }

Interestingly, for proxy_pass port is not necessary to specify, I think due to the indication of https://

With this configuration, any stack that nginx maintains can be wiped out of the available stacks, and nginx will not send host not found in upstream message when restarted