How to solve 502 bad gateway error?

Question

I am trying to access my project locally and I keep getting 502 bad gateway nginx error. Funny thing is that the admin side works but, the customer view gives me this bad gateway error.

I am using nginx and the error logs from nginx are

2022/10/02 12:04:58 [alert] 1353#1353: *37 open socket #11 left in connection 9
2022/10/02 12:04:58 [alert] 1353#1353: *39 open socket #27 left in connection 12
2022/10/02 12:04:58 [alert] 1353#1353: aborting
2022/10/02 12:38:09 [alert] 16747#16747: *109 open socket #25 left in connection 9
2022/10/02 12:38:09 [alert] 16747#16747: *114 open socket #26 left in connection 10
2022/10/02 12:38:09 [alert] 16747#16747: aborting
2022/10/02 12:38:09 [emerg] 21941#21941: unknown directive "^[[200~fastcgi_buffers" in /etc/nginx/nginx.conf:63
2022/10/02 12:38:15 [emerg] 21985#21985: unknown directive "^[[200~fastcgi_buffers" in /etc/nginx/nginx.conf:63
2022/10/02 12:49:33 [alert] 22391#22391: *4 open socket #25 left in connection 5
2022/10/02 12:49:33 [alert] 22391#22391: *11 open socket #27 left in connection 6
2022/10/02 12:49:33 [alert] 22391#22391: aborting
2022/10/02 12:49:33 [emerg] 23808#23808: "fastcgi_buffers" directive is duplicate in /etc/nginx/nginx.conf:66

My nginx conf are

user www-data;
worker_processes auto;
pid /run/nginx.pid;
include /etc/nginx/modules-enabled/*.conf;

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;
        fastcgi_buffering on;
        fastcgi_buffers 4 256k;
        fastcgi_buffer_size 128k;
        # server_tokens off;

        # server_names_hash_bucket_size 64;
        # server_name_in_redirect off;

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

        ##
        # SSL Settings
        ##

        ssl_protocols TLSv1 TLSv1.1 TLSv1.2 TLSv1.3; # Dropping SSLv3, ref: POODLE
        ssl_prefer_server_ciphers on;

        ##
        # Logging Settings
        ##

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

        ##
        # Gzip Settings
        ##
         gzip on;

        # 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/javascript text/xml application/xml application/xml+rss text/javascript;

        ##
        # Virtual Host Configs
        ##

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


#mail {
#       # See sample authentication script at:
#       # http://wiki.nginx.org/ImapAuthenticateWithApachePhpScript
# 
#       # auth_http localhost/auth.php;
#       # pop3_capabilities "TOP" "USER";
#       # imap_capabilities "IMAP4rev1" "UIDPLUS";
# 
#       server {
#               listen     localhost:110;
#               protocol   pop3;
#               proxy      on;
#       }
# 
#       server {
#               listen     localhost:143;
#               protocol   imap;
#               proxy      on;
#       }
#}

and my nginx configurations for my magento project are

server {
    listen 80;
    listen [::]:80;
    server_name hyva.local;

    access_log /var/www/hyva/logs/access.log;
    error_log /var/www/hyva/logs/error.log;

    set $MAGE_ROOT /var/www/hyva/public;
    root $MAGE_ROOT/pub;

    index index.php;
    autoindex off;
    charset UTF-8;
    error_page 404 403 = /errors/404.php;

    # PHP entry point for setup application
    location ~* ^/setup($|/) {
        root $MAGE_ROOT;
        location ~ ^/setup/index.php {
            fastcgi_pass   unix:/var/run/php/php8.0-fpm.sock;

            fastcgi_param  PHP_FLAG  "session.auto_start=off \n suhosin.session.cryptua=off";
            fastcgi_param  PHP_VALUE "memory_limit=756M \n max_execution_time=600";
            fastcgi_read_timeout 600s;
            fastcgi_connect_timeout 600s;

            fastcgi_index  index.php;
            fastcgi_param  SCRIPT_FILENAME  $document_root$fastcgi_script_name;
            include        fastcgi_params;
        }

        location ~ ^/setup/(?!pub/). {
            deny all;
        }

        location ~ ^/setup/pub/ {
            add_header X-Frame-Options "SAMEORIGIN";
        }
    }

    # PHP entry point for update application
    location ~* ^/update($|/) {
        root $MAGE_ROOT;

        location ~ ^/update/index.php {
            fastcgi_split_path_info ^(/update/index.php)(/.+)$;
            fastcgi_pass   unix:/var/run/php/php8.0-fpm.sock;
            fastcgi_index  index.php;
             fastcgi_param  SCRIPT_FILENAME  $document_root$fastcgi_script_name;
            fastcgi_param  PATH_INFO        $fastcgi_path_info;
            include        fastcgi_params;
        }

        # Deny everything but index.php
        location ~ ^/update/(?!pub/). {
            deny all;
        }

        location ~ ^/update/pub/ {
            add_header X-Frame-Options "SAMEORIGIN";
        }
    }

    location / {
        try_files $uri $uri/ /index.php$is_args$args;
    }

    location /pub/ {
        location ~ ^/pub/media/(downloadable|customer|import|theme_customization/.*\.xml) {
            deny all;
        }
        alias $MAGE_ROOT/pub/;
        add_header X-Frame-Options "SAMEORIGIN";
    }

    location /static/ {
        # Uncomment the following line in production mode
        # expires max;

        # Remove signature of the static files that is used to overcome the browser cache
        location ~ ^/static/version {
            rewrite ^/static/(version[^/]+/)?(.*)$ /static/$2 last;
        }

        location ~* \.(ico|jpg|jpeg|png|gif|svg|js|css|swf|eot|ttf|otf|woff|woff2|json)$ {
            add_header Cache-Control "public";
            add_header X-Frame-Options "SAMEORIGIN";
            expires +1y;

            if (!-f $request_filename) {
                rewrite ^/static/?(.*)$ /static.php?resource=$1 last;
            }
        }
        location ~* \.(zip|gz|gzip|bz2|csv|xml)$ {
            add_header Cache-Control "no-store";
            add_header X-Frame-Options "SAMEORIGIN";
             expires    off;

            if (!-f $request_filename) {
               rewrite ^/static/?(.*)$ /static.php?resource=$1 last;
            }
        }
        if (!-f $request_filename) {
            rewrite ^/static/?(.*)$ /static.php?resource=$1 last;
        }
        add_header X-Frame-Options "SAMEORIGIN";
    }

    location /media/ {
        try_files $uri $uri/ /get.php$is_args$args;

        location ~ ^/media/theme_customization/.*\.xml {
            deny all;
        }

        location ~* \.(ico|jpg|jpeg|png|gif|svg|js|css|swf|eot|ttf|otf|woff|woff2)$ {
            add_header Cache-Control "public";
            add_header X-Frame-Options "SAMEORIGIN";
            expires +1y;
            try_files $uri $uri/ /get.php$is_args$args;
        }
        location ~* \.(zip|gz|gzip|bz2|csv|xml)$ {
            add_header Cache-Control "no-store";
            add_header X-Frame-Options "SAMEORIGIN";
            expires    off;
            try_files $uri $uri/ /get.php$is_args$args;
        }
        add_header X-Frame-Options "SAMEORIGIN";
    }

    location /media/customer/ {
        deny all;
    }

    location /media/downloadable/ {
        deny all;
    }
 location /media/import/ {
        deny all;
    }

    # PHP entry point for main application
    location ~ (index|get|static|report|404|503|health_check)\.php$ {
        try_files $uri =404;
        fastcgi_pass unix:/var/run/php/php8.0-fpm.sock;
        fastcgi_buffers 16 1024k;
        fastcgi_buffer_size 1024k;

        fastcgi_param  PHP_FLAG  "session.auto_start=off \n suhosin.session.cryptua=off";
        fastcgi_param  PHP_VALUE "memory_limit=756M \n max_execution_time=18000";
        fastcgi_read_timeout 600s;
        fastcgi_connect_timeout 600s;

        fastcgi_index  index.php;
        fastcgi_param  SCRIPT_FILENAME  $document_root$fastcgi_script_name;
        include        fastcgi_params;
    }

    gzip off;

    # Banned locations (only reached if the earlier PHP entry point regexes don't match)
    location ~* (\.php$|\.htaccess$|\.git) {
        deny all;
    }
}

No idea how I can solve this problem.

Answer 1

Please once find the app/bootstrap.php file and uncomment the error display line

#ini_set('display_errors', 1);

Then you can verify what is causing the issue.

if you what to verify that the 502 issue was caused due to server config then try replacing or adding exit(); in the index.php file with a custom message that works then issue is with Magento2 and most of the time its a permission issue (var, generated, and media)

That's my opinion might help you

Happy coding