Nginx 502 Bad Gateway error when using proxy

Question

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?

Are these running on same nginx or different nginx? Also did you make an entry for `api.example.com` in the hosts file? Are you using websockets also? If yes then which path? — Tarun Lalwani, Dec 12 '17 at 15:17
Building on where Tarun was maybe leading, the error on too many workers could indicate a loop in how frontend is proxying, could it be sending requests to itself if hostnames are not configured properly. But the connection reset by peer is different, and could be legitimate error in server side code execution. Do you have logs from each nginx instance, what about php engine. Does a call directly to backend work? — Eddie, Dec 12 '17 at 18:24

score 0 · Answer 1 · answered Dec 10 '17 at 08:41

0

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

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

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

answered Dec 10 '17 at 08:41

ALI Emamian

35
6

For which config is this, backend or frontend? And what are the multiple ip's for? Could you maybe write this how it would look in my config file? – J.Koppen Dec 11 '17 at 11:06
Downvote: Proxy_pass is configured in front end, your example adds load balancing which OP may not need. Backend is using CGI to act as PHP, proxy_pass not required there. – Eddie Dec 12 '17 at 18:16

score 0 · Answer 2 · answered Dec 12 '17 at 19:11

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;
        }
}

HI Eddie, thanks for your detailed response. I'll try this once i have time. Thank you very much nonetheless! — J.Koppen, Dec 12 '17 at 20:27
Hi Eddie, i just gave it a shot and with this configuration i can't access the url's.. When I browse to example.com or api.example.com i get a ERR_CONNECTION_REFUSED. However, it does work when put the ports behind it like example.com:8080 or api.example.com:8081. Any idea how to solve this? — J.Koppen, Dec 13 '17 at 20:58
Sorry, I was using 8080 locally as I run nginx as non-root. by default api.example.com will be port 80, or port 443 for https. Just change the ports you have frontend listening on to 80, you can leave backend the same as frontend knows to use that port. — Eddie, Jan 09 '18 at 17:47

score 0 · Answer 3 · answered Jun 03 '20 at 15:19

0

I had a similar problem, solved it with:

events {
    worker_connections 1024;
}

The events block goes the same level of the http block.

answered Jun 03 '20 at 15:19

Washington Guedes

4,254
3
30
56

Nginx 502 Bad Gateway error when using proxy

3 Answers3

Linked