Nginx 502 Bad Gateway error when using proxy

问题:

i have a Angular build and an Laravel backend providing API's running on one server. I've configured them in nginx with the frontend having a proxy to the backend server.

The backend is running on the url (example is placeholder) http://api.example.com and the frontend is running on http://example.com

Frontend config:

server {
    listen       80;
    server_name  example.com;

    location /api {
        proxy_pass http://api.example.com;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
        proxy_set_header Host $host;
    }

    location / {
        root  /var/www/angular/em-frontend/dist;
        index  index.html index.htm;
        try_files $uri $uri/ /index.html$is_args$args;
    }
}

Backend config:

server {
        listen 80;
        server_name api.example.com;

        root /var/www/angular/em-backend/public;

        index index.php index.html index.htm;

        location / {
                # First attempt to serve request as file, then
                # as directory, then fall back to displaying a 404.
                try_files $uri $uri/ /index.php?$query_string;
                # Uncomment to enable naxsi on this location
                # include /etc/nginx/naxsi.rules
        }
        location ~ \.php$ {
                try_files $uri =404;
                fastcgi_split_path_info ^(.+\.php)(/.+)$;
                fastcgi_pass unix:/var/run/php/php7.0-fpm.sock;
                fastcgi_index index.php;
                fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
                include fastcgi_params;
        }
}

Now when I do any api call from the frontend I get the a 502 Bad Gateway error from nginx.

From nginx error log:

2017/12/09 23:30:40 [alert] 5932#5932: 768 worker_connections are not enough
2017/12/09 23:30:40 [error] 5932#5932: *770 recv() failed (104: Connection reset by peer) while reading response header from upstream, client: IP_MASKED, server: example.com, request: "GET /api/endpoint HTTP/1.1", upstream: "http://IP_ADDRESS:80/api/endpoint", host: "example.com", referrer: "http://example.com/dashboard"

Any idea how I can fix this?

回答1:

you must use proxy-pass in location block like this example:

upstream myproject {
   server ip1 ;
   server ip2 ;
   server ip3 ;

} 
location / { 
   proxy_pass      http://myproject;
}

回答2:

I believe your issue is hostname configuration creating a recursive loop in which a single request is proxied back to the front-end quickly exhausting all workers. You'll recognize this by a single request to the frontend generating many entries in the access log.

I was able to quickly recreate that error using the config you provided. Below is a modified version that eliminates config serving up 2 different static files on backend server to illustrate the minimum config required. If this works, you can add the cgi_pass config back in.

#set api domain to use alternate port, could also just tack onto proxy_pass.
upstream api.example.com {
    server localhost:8081;
}

#frontend listening on port 8080
server {
    listen       8080;
    server_name  example.com;

    location /api {
        proxy_pass http://api.example.com;
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
        proxy_set_header Host $host;
    }

    location / {
        root  /usr/local/var/www;
        index  index.html index.htm;
        try_files $uri $uri/ /index.html$is_args$args;
    }
}

#backend listening on 8081
server {
        listen 8081;
        server_name api.example.com;

        index index.php index.html index.htm;

        location / {  # will match any url not ending in .php
              root  /usr/local/var/www;
              try_files $uri $uri/ /index.html;
        }
        location ~ \.php { #successfully responds to http://example.com:8080/api/*.php
              root  /usr/local/var/www;
              try_files $uri $uri/ /service.html;
        }
}