proxy_pass to websocket behind nginx

Question

I got websocket servers and there are behind nginx. I need to configure second nginx as proxy to this first nginx. But when I make a request, there is an error 400 or 404 (with different configs).

Here is my config of my nginx:

map $http_upgrade $is_upgrade {
default upgrade;
''      '';
}

upstream websocket {
    server [here_is_address];
}

server {
    listen 80 default;
    location /ws/ {         
        proxy_http_version 1.1;
        client_max_body_size 50m;
        proxy_read_timeout 60s;
        proxy_set_header Host $http_host;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection $is_upgrade;
        proxy_pass http://websocket;
    }
}