Nginx Reverse Proxy: Throwing 502 Bad Gateway

I was following this tutorial to learn about Reverse Proxy https://www.youtube.com/watch?v=ZmH1L1QeNHk&t=227s

I'm running the docker image like this

sudo docker run -d --name nginx-base -p 80:80 nginx:latest

I was able to edit the default.conf Here is the file

server {
    listen       80;
    listen  [::]:80;
    server_name  localhost;

    #access_log  /var/log/nginx/host.access.log  main;

    location / {
        root   /usr/share/nginx/html;
        index  index.html index.htm;
    }

    location /test {
        proxy_pass http://localhost:8086/test;
    }

    location /home {
        proxy_pass http://localhost:3000;
    }

   location /home/auth {
        proxy_pass http://localhost:3000/auth;
    }

    #error_page  404              /404.html;

    # redirect server error pages to the static page /50x.html
    #
    error_page   500 502 503 504  /50x.html;
    location = /50x.html {
        root   /usr/share/nginx/html;
    }

    # proxy the PHP scripts to Apache listening on 127.0.0.1:80
    #
    #location ~ \.php$ {
    #    proxy_pass   http://127.0.0.1;
    #}

    # pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
    #
    #location ~ \.php$ {
    #    proxy_pass   http://127.0.0.1;
    #}
    
    # pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
    #
    #location ~ \.php$ {
    #    root           html;
    #    fastcgi_pass   127.0.0.1:9000;
    #    fastcgi_index  index.php;
    #    fastcgi_param  SCRIPT_FILENAME  /scripts$fastcgi_script_name;
    #    include        fastcgi_params;
    #}
    
    # deny access to .htaccess files, if Apache's document root
    # concurs with nginx's one
    #
    #location ~ /\.ht {
    #    deny  all;
    #}
}
     
    

I get the Nginx Welcome screen, when I go to http://localhost/

But when I try to access http://localhost/test or http://localhost/home

Also, I'm able to access localhost:3000 and localhost:8086/test

Not sure why nginx is throwing 502, did I miss any configuration?

🤨 There is a really very few info about tuning up Nginx Proxy Manager. So let's take a look at common issues/errors:

Welcome to nginx default page

Thats happens because your nginx/app container files not volumed to /usr/share/nginx/html. By default NPM use this root location, not /var/www/.... Just add the right volume to your container.

502 Bad Gateway error

This is a complex issue. First of all make sure you volumed to the /data folder docs

- ./data:/data

💡 ⚠️ If folder is volumed, you can see Nginx Proxy Manager errors log in your folder /your/docker/path/data/logs/proxy-host-1_error.log. In my case error was:

peer closed connection in SSL handshake while SSL handshaking to upstream, client: [bla-bla-bla]

⚡ The reason was because in Proxy Host edit at SSL tab i didnt checked Force SSL and HTTP/2 Support (if you use HTTPS/SSL/443 port).

👉 Full guide how to tune up your host in NPM with HTTPS/SSL:

1️⃣ You have to setup Nginx Proxy Manager via Docker and start a container. See setup docs. An example with MySQL storage:

services:
  app:
    image: 'jc21/nginx-proxy-manager:latest'
    restart: unless-stopped
    ports:
      - '80:80'
      - '81:81'
      - '443:443'
    environment:
      DB_MYSQL_HOST: "db"
      DB_MYSQL_PORT: 3306
      DB_MYSQL_USER: ${DB_USER}
      DB_MYSQL_PASSWORD: ${DB_PASS}
      DB_MYSQL_NAME: ${DB_NAME}
    volumes:
      - ./data:/data
      - ./letsencrypt:/etc/letsencrypt
  db:
    image: 'jc21/mariadb-aria:latest'
    restart: unless-stopped
    environment:
      MYSQL_ROOT_PASSWORD: ${DB_ROOT_PASSWORD}
      MYSQL_USER: ${DB_USER}
      MYSQL_PASSWORD: ${DB_PASS}
      MYSQL_DATABASE: ${DB_NAME}
    volumes:
      - ./mysql:/var/lib/mysql

Dont forget to create .env file with MySQL variables values.

Run docker compose up -d --build and you can go to http://your-ip:81 and see NPM GUI.

Default access data:

admin@example.com - login/email
changeme - password

2️⃣ You have your nginx/app container with:

• linked app files to /usr/share/nginx/html via volume, example:

    volumes:
      - "./my/app/files:/usr/share/nginx/html"
  

• ports: YOUR_HTTP_PORT_NUM:80, YOUR_HTTPS_PORT_NUM:443, example:

    ports:
      - "8093:80"
      - "9201:443"
  

⚠️ 8093 and 9201 ports are just examples

3️⃣ In Nginx Proxy Manager admin panel go to Hosts -> Proxy Hosts -> Add Proxy Host

Details tab

• Domain Names: add your domain name [with the same IP/A-record as NPM has], for example mydomain.com
• Scheme: http [no matter if you use HTTPS]
• Forward Hostname/IP: mydomain.com [not docker container name or IP or localhost or 127.0.0.1]
• Forward Port: your HTTP container port, in this case is 8093

SSL tab

• SSL Certificate: Request a new SSL Certificate [or choose an exists one]
• Force SSL: check it [important!]
• HTTP/2 Support: check it

Advanced tab

Leave empty, if you really don't know how to manage it in NPM.

Hope that helps!