502 Bad Gateway & Upstream connection refused

2024-01-24 10:25:11 nginx.1     | whoami.local 192.168.65.1 - - [24/Jan/2024:15:25:11 +0000] "GET / HTTP/1.1" 502 157 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:121.0) Gecko/20100101 Firefox/121.0" "172.18.0.3:8400"
2024-01-24 10:25:11 nginx.1     | 2024/01/24 15:25:11 [error] 25#25: *1 connect() failed (111: Connection refused) while connecting to upstream, client: 192.168.65.1, server: whoami.local, request: "GET / HTTP/1.1", upstream: "http://172.18.0.3:8400/", host: "whoami.local"

version: '3'

services:
  proxy:
    image: nginxproxy/nginx-proxy:1.4
    build:
      context: ./
      dockerfile: Dockerfile
    ports:
      - "80:80"
    volumes:
      - /var/run/docker.sock:/tmp/docker.sock:ro
    networks:
      - nginx-proxy
    restart: always

networks:
  nginx-proxy:
    name: local-dev
    driver: bridge

version: '3'

services:

  whoami:
    image: jwilder/whoami
    expose:
      - "8400"
    environment:
      - VIRTUAL_HOST=whoami.local
      - VIRTUAL_PORT=8400
    networks:
      - local-dev

networks:
  local-dev:
    external: true

127.0.0.1    whoami.local

# nginx-proxy version : 1.4.0-71-gd46881f
# Networks available to the container running docker-gen (which are assumed to
# match the networks available to the container running nginx):
#     local-dev
# If we receive X-Forwarded-Proto, pass it through; otherwise, pass along the
# scheme used to connect to this server
map $http_x_forwarded_proto $proxy_x_forwarded_proto {
    default $http_x_forwarded_proto;
    '' $scheme;
}
map $http_x_forwarded_host $proxy_x_forwarded_host {
    default $http_x_forwarded_host;
    '' $host;
}
# If we receive X-Forwarded-Port, pass it through; otherwise, pass along the
# server port the client connected to
map $http_x_forwarded_port $proxy_x_forwarded_port {
    default $http_x_forwarded_port;
    '' $server_port;
}
# If the request from the downstream client has an "Upgrade:" header (set to any
# non-empty value), pass "Connection: upgrade" to the upstream (backend) server.
# Otherwise, the value for the "Connection" header depends on whether the user
# has enabled keepalive to the upstream server.
map $http_upgrade $proxy_connection {
    default upgrade;
    '' $proxy_connection_noupgrade;
}
map $upstream_keepalive $proxy_connection_noupgrade {
    # Preserve nginx's default behavior (send "Connection: close").
    default close;
    # Use an empty string to cancel nginx's default behavior.
    true '';
}
# Abuse the map directive (see <https://stackoverflow.com/q/14433309>) to ensure
# that $upstream_keepalive is always defined.  This is necessary because:
#   - The $proxy_connection variable is indirectly derived from
#     $upstream_keepalive, so $upstream_keepalive must be defined whenever
#     $proxy_connection is resolved.
#   - The $proxy_connection variable is used in a proxy_set_header directive in
#     the http block, so it is always fully resolved for every request -- even
#     those where proxy_pass is not used (e.g., unknown virtual host).
map "" $upstream_keepalive {
    # The value here should not matter because it should always be overridden in
    # a location block (see the "location" template) for all requests where the
    # value actually matters.
    default false;
}
# Apply fix for very long server names
server_names_hash_bucket_size 128;
# Default dhparam
ssl_dhparam /etc/nginx/dhparam/dhparam.pem;
# Set appropriate X-Forwarded-Ssl header based on $proxy_x_forwarded_proto
map $proxy_x_forwarded_proto $proxy_x_forwarded_ssl {
    default off;
    https on;
}
gzip_types text/plain text/css application/javascript application/json application/x-javascript text/xml application/xml application/xml+rss text/javascript;
log_format vhost '$host $remote_addr - $remote_user [$time_local] "$request" $status $body_bytes_sent "$http_referer" "$http_user_agent" "$upstream_addr"';
access_log off;
    ssl_protocols TLSv1.2 TLSv1.3;
    ssl_ciphers 'ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384:DHE-RSA-CHACHA20-POLY1305';
    ssl_prefer_server_ciphers off;
error_log /dev/stderr;
resolver 127.0.0.11;
# HTTP 1.1 support
proxy_http_version 1.1;
proxy_set_header Host $host;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection $proxy_connection;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Host $proxy_x_forwarded_host;
proxy_set_header X-Forwarded-Proto $proxy_x_forwarded_proto;
proxy_set_header X-Forwarded-Ssl $proxy_x_forwarded_ssl;
proxy_set_header X-Forwarded-Port $proxy_x_forwarded_port;
proxy_set_header X-Original-URI $request_uri;
# Mitigate httpoxy attack (see README for details)
proxy_set_header Proxy "";
server {
    server_name _; # This is just an invalid value which will never trigger on a real hostname.
    server_tokens off;
    access_log /var/log/nginx/access.log vhost;
    http2 on;
    listen 80;
    listen 443 ssl;
    ssl_session_cache shared:SSL:50m;
    ssl_session_tickets off;
    # No default.crt certificate found for this vhost, so force nginx to emit a
    # TLS error if the client connects via https.
    ssl_ciphers aNULL;
    set $empty "";
    ssl_certificate data:$empty;
    ssl_certificate_key data:$empty;
    if ($https) {
        return 444;
    }
    return 503;
}
# whoami.local/
upstream whoami.local {
    # Container: test-whoami-1
    #     networks:
    #         local-dev (reachable)
    #     IP address: 172.18.0.3
    #     exposed ports: 8000/tcp 8400/tcp
    #     default port: 80
    #     using port: 8400
    server 172.18.0.3:8400;
}
server {
    server_name whoami.local;
    access_log /var/log/nginx/access.log vhost;
    http2 on;
    listen 80 ;
    listen 443 ssl ;
    # No certificate found for this vhost, so force nginx to emit a TLS error if
    # the client connects via https.
    ssl_ciphers aNULL;
    set $empty "";
    ssl_certificate data:$empty;
    ssl_certificate_key data:$empty;
    if ($https) {
        return 444;
    }
    location / {
        proxy_pass http://whoami.local;
        set $upstream_keepalive false;
    }
}