Error during WebSocket handshake: Unexpected response code: 301 - nginx

Question

I have already looked into the answer to RoR 5.0.0 ActionCable wss WebSocket handshake: Unexpected response code: 301 but it was not applicable to my case.
I use an nginx-proxy as a front for several web-servers running in docker-containers. I use the nginx-config-template from https://github.com/jwilder/nginx-proxy
Now in my docker-container I have another nginx with the following config:
map $http_upgrade $connection_upgrade {
default upgrade;
'' close;
}
upstream websocket {
server my-websocket-docker-container:8080;
}
server {
root /src/html;
location /websocket/ {
resolver 127.0.0.11 ipv6=off;
proxy_pass http://websocket;
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection $connection_upgrade;
}
location / {
# try to serve file directly, fallback to index.php
try_files $uri /index.php$is_args$args;
}
...
}
When trying to connect to wss://example.com/websocket I get the aforementioned error about unexpected response code 301. When I curl the websocket-url manually I can see the nginx response telling me "301 moved permanantly". But why? Where is this coming from?
Can anybody help? Thanks!

Answer 1

I was facing a similar issue today. I was using the "classic" WebSocket API and NGINX to test the connection between some services. I came up with the following solution:
WebSocket instance creation:
const websocket = new WebSocket('ws://' + window.location.host + '/path');
Nginx config:
location /path {
proxy_pass http://websocket:port;
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection "upgrade";
}
Where:
path is the path to be redirected
websocket is the hostname or the IP of the host
port is the port where the application is served on the host