connect() failed (111: Connection refused) while connecting to upstream

I'm experiencing 502 Gateway errors when accessing a PHP file in a directory (http://example.com/dev/index.php). The logs simply says this:

2011/09/30 23:47:54 [error] 31160#0: *35 connect() failed (111: Connection refused) while connecting to upstream, client: xx.xx.xx.xx, server: domain.com, request: "GET /dev/ HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "domain.com"

I've never experienced this before. What is the solution for this type of 502 Gateway error?

This is the nginx.conf:

user www-data;
worker_processes 4;
pid /var/run/nginx.pid;

events {
    worker_connections 768;
    # multi_accept on;
}

http {

    ##
    # Basic Settings
    ##

    sendfile on;
    tcp_nopush on;
    tcp_nodelay on;
    keepalive_timeout 65;
    types_hash_max_size 2048;
    # server_tokens off;

    # server_names_hash_bucket_size 64;
    # server_name_in_redirect off;

    include /etc/nginx/mime.types;
    default_type application/octet-stream;

    ##
    # Logging Settings
    ##

    access_log /var/log/nginx/access.log;
    error_log /var/log/nginx/error.log;

    ##
    # Gzip Settings
    ##

    gzip on;
    gzip_disable "msie6";

    # gzip_vary on;
    # gzip_proxied any;
    # gzip_comp_level 6;
    # gzip_buffers 16 8k;
    # gzip_http_version 1.1;
    # gzip_types text/plain text/css application/json application/x-javascript text/xml application/xml application/xml+rss text/javascript;

    ##
    # Virtual Host Configs
    ##

    include /etc/nginx/conf.d/*.conf;
    include /etc/nginx/sites-enabled/*;
}

It sounds like you haven't started and configured the backend for Nginx. Start php-fpm and add the following to nginx.conf, in the http context:

server {
    listen 127.0.0.1;
    server_name localhost;

    error_log /var/log/nginx/localhost.error_log info;

    root /var/www/localhost/htdocs;

    location ~ \.php$ {
        fastcgi_pass 127.0.0.1:9000;
        include /etc/nginx/conf.d/*.conf;
        include /etc/nginx/sites-enabled/*;

        fastcgi_intercept_errors        on;
        error_page 404 /error/404.php;
    }
}

This answer is only for those who get an error like this:

connect() failed (111: Connection refused) while connecting to upstream, client .... fastcgi://[::1]:9000

Rewrite your nginx config to use ip, not dns. For instance, 127.0.0.1 instead of localhost, or remove the ipv6 alias from /etc/hosts.

Got errors like this too. Problem was my abstract backend referencing two servers. php-fpm was only listing to socket...

# Upstream to abstract backend connection(s) for php
upstream php {
        server unix:/var/run/php5-fpm.sock;
        #server 127.0.0.1:9000;
} 

server {
    [...]

    location ~ \.php$ {
            # NOTE: You should have "cgi.fix_pathinfo = 0;" in php.ini

            # With php5-fpm:
            fastcgi_pass php;
            fastcgi_index index.php;
            fastcgi_intercept_errors on;
            include fastcgi_params;
    }
}

Had the same problem with proxied requests to a Node server listening on port 5000. Requests would result with 200 OK but sometime 502 Bad Gateway randomly. NGINX showed the error:

connect() failed (111: Connection refused) while connecting to upstream, client: ..., server: ...

My solution:

1. Set node HTTP server to listen strictly for ipv4 by including localhost as host: server.listen(5000, 'localhost');
2. Removed any ipv6 listen directives (listen [::]:80; or listen [::]:443 ssl default_server;).
3. Changed location block proxy_pass to use IPs: proxy_pass http://127.0.0.1:5000 (not proxy_pass http://localhost:5000).

Hope this helps someone.