asp.netnginxswagger-uikestrel-http-serverbad-gateway

502 bad gateway nginx for dotnet WebApplication

I am trying to run a test WebApplication on a Digital Ocean droplet running Centos9 Stream and Nginx The WebApplication is the default project created from the visual studio template. It uses net8.0. Microsoft.AspNetCore.OpenApi 7.0.14 and Swashbuckle.AspNetCore 6.5.0

I also installed a certificate via LetsEncrypt

After starting nginx on the droplet I also start the application using

DotNet WebApplication.dll

and see that it is listening on port 5000

listening on port 5000

However if I try

curl -I https://example.com

I get

   HTTP/1.1 502 Bad Gateway
   Server: nginx/1.22.1

And I see the WebApplication console outputs a warning

Microsoft.AspNetCore.HttpsPolicy.HttpsRedirectionMiddleware[3]
Failed to determine the https port for redirect

I have the following in /etc/nginx/nginx.conf

# For more information on configuration, see:
#   * Official English Documentation: http://nginx.org/en/docs/
#   * Official Russian Documentation: http://nginx.org/ru/docs/

user nginx;
worker_processes auto;
error_log /var/log/nginx/error.log notice;
pid /run/nginx.pid;

# Load dynamic modules. See /usr/share/doc/nginx/README.dynamic.
include /usr/share/nginx/modules/*.conf;

events {
    worker_connections 1024;
}

http {
    log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                      '$status $body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';

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

    sendfile            on;
    tcp_nopush          on;
    keepalive_timeout   65;
    types_hash_max_size 4096;

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

    # Load modular configuration files from the /etc/nginx/conf.d directory.
    # See http://nginx.org/en/docs/ngx_core_module.html#include
    # for more information.
    include /etc/nginx/conf.d/*.conf;

    server {
        server_name example.com;
        location / {
            proxy_pass         http://localhost:5000; # Your .NET app's URL
            proxy_http_version 1.1;
            proxy_set_header   Upgrade $http_upgrade;
            proxy_set_header   Connection keep-alive;
            proxy_set_header   Host $host;
            proxy_cache_bypass $http_upgrade;
            proxy_set_header   X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_set_header   X-Forwarded-Proto $scheme;
        }


        root         /usr/share/nginx/html;

        # Load configuration files for the default server block.
        include /etc/nginx/default.d/*.conf;

        error_page 404 /404.html;
        location = /404.html {
        }

        error_page 500 502 503 504 /50x.html;
        location = /50x.html {
        }
    
    listen [::]:443 ssl ipv6only=on; # managed by Certbot
    listen 443 ssl; # managed by Certbot
    ssl_certificate /etc/letsencrypt/live/example.com/fullchain.pem; # managed by Certbot
    ssl_certificate_key /etc/letsencrypt/live/examplecom/privkey.pem; # managed by Certbot
    include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
    ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot

}

# Settings for a TLS enabled server.
#
#    server {
#        listen       443 ssl http2;
#        listen       [::]:443 ssl http2;
#        server_name  _;
#        root         /usr/share/nginx/html;
#
#        ssl_certificate "/etc/pki/nginx/server.crt";
#        ssl_certificate_key "/etc/pki/nginx/private/server.key";
#        ssl_session_cache shared:SSL:1m;
#        ssl_session_timeout  10m;
#        ssl_ciphers PROFILE=SYSTEM;
#        ssl_prefer_server_ciphers on;
#
#        # Load configuration files for the default server block.
#        include /etc/nginx/default.d/*.conf;
#
#        error_page 404 /404.html;
#        location = /404.html {
#        }
#
#        error_page 500 502 503 504 /50x.html;
#        location = /50x.html {
#        }
#    }



    server {
    if ($host = example.com) {
        return 301 https://$host$request_uri;
    } # managed by Certbot


        listen       80;
        listen       [::]:80;
        server_name example.com;
    return 404; # managed by Certbot


}}

[Update]

cat /var/log/nginx/error.log

reports

Permission denied while connecting to upstream

[Update]

After looking at this ticket I tried

setsebool -P httpd_can_network_connect 1

And restarted.

Now when I run

dotnet WebApplication.dll

I get a warning

Microsoft.AspNetCore.HttpsPolicy.HttpsRedirectionMiddleware[3]
failed to deterimine the https port for redirect.
Microsoft.Hosting.Lifetime[0]
Application is shutting down.

And I still get the 502 Bad Gateway error on

curl -I https://example.com

I no longer see the Permission Denied error in the log. It is ( with IPAddress obfuscated )

2024/01/06 04:39:52 [notice] 1323#1323: signal 3 (SIGQUIT) received from 1, shutting down
2024/01/06 04:39:52 [notice] 1323#1323: signal 17 (SIGCHLD) received from 1324
2024/01/06 04:39:52 [notice] 1323#1323: worker process 1324 exited with code 0
2024/01/06 04:39:52 [notice] 1323#1323: exit
2024/01/06 04:43:25 [notice] 1339#1339: using the "epoll" event method
2024/01/06 04:43:25 [notice] 1339#1339: nginx/1.22.1
2024/01/06 04:43:25 [notice] 1339#1339: built by gcc 11.3.1 20221121 (Red Hat 11.3.1-4) (GCC) 
2024/01/06 04:43:25 [notice] 1339#1339: OS: Linux 5.14.0-391.el9.x86_64
2024/01/06 04:43:25 [notice] 1339#1339: getrlimit(RLIMIT_NOFILE): 1024:524288
2024/01/06 04:43:25 [notice] 1340#1340: start worker processes
2024/01/06 04:43:25 [notice] 1340#1340: start worker process 1341
2024/01/06 05:00:14 [error] 1341#1341: *5 connect() failed (111: Connection refused) while connecting to upstream, client: MyIPAddress, server: example.com, request: "HEAD / HTTP/1.1", upstream: "http://127.0.0.1:5000/", host: "example.com"
2024/01/06 05:00:14 [warn] 1341#1341: *5 upstream server temporarily disabled while connecting to upstream, client: MyIPAddress, server: example.com, request: "HEAD / HTTP/1.1", upstream: "http://127.0.0.1:5000/", host: "example.com"
2024/01/06 05:00:14 [error] 1341#1341: *5 connect() failed (111: Connection refused) while connecting to upstream, client: MyIPAddress, server: example.com, request: "HEAD / HTTP/1.1", upstream: "http://[::1]:5000/", host: "example.com"
2024/01/06 05:00:14 [warn] 1341#1341: *5 upstream server temporarily disabled while connecting to upstream, client: MyIPAddress, server: example.com, request: "HEAD / HTTP/1.1", upstream: "http://[::1]:5000/", host: "example.com"

[Update]

I see that https is not mentioned in the published appsettings.json (whereas it is in the development launchsettings.json)

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft.AspNetCore": "Warning"
    }
  },
  "AllowedHosts": "*"
}

[Update] From here I learned that

If no ports are specified, Kestrel binds to http://localhost:5000.

Next step adding

  "Kestrel": {
    "Endpoints": {
      "Https": {
        "Url": "https://localhost:5000"
      }
    }
  },

Now I get

The ASP.NET developer certificate is not trusted. See this

Also the Bad Gateway is still not solved.

[Update]

I have solved the certificate issue by making both nginx.conf and appsettings.json use http://localhost:5000

I still get the 502 Bad Gateway

https://example.com/swagger/index.html gives

nginx error. The page you are looking for is temporarily unavailable.

[Update]

I enabled IPV6 on the droplet (after noticing it was On in nginx.conf)

Now

curl -I https://example.com

reports 404 Not Found

Also the WebApplication console warns

Microsoft.AspNetCore.HttpsPolicy.HttpsRedirectionMiddleware3 Failed to determine the https port for redirect.

I can see using

cat /var/log/nginx/error.log

that

SSL_do_handshake() failed (SSL:error0A00006C:SSL routines::bad key share) while SSL Handshaking

[Update]

After reading ozkanpakdil's comment, I changed program.cs to remove app.UseHttpsRedirection();

Now

curl -I example.com

gives

301 Moved Permanently

[Update]

I am wondering about the disabled words in the status nginx output.

nginx status

If I end the WebApplication and go to example.com in the browser I get an error page

error page

If I start the WebApplication and go to example.com I see

Failed to load resource: the server responded with a status of 404.

On my development machine in Visual Studio the app opens https://localhost:7223/swagger/index.html

[Update]

To get proper resolution on example.com I needed to change the demo code to use the swagger ui

UseSwaggerUI

Solution