Why does the subdomain redirect requests back to parent domain?-CodePudding

I have a subdomain sub.example.com that is hosted on an EC2 instance.

In the AWS Route53 console I've created an A-record that points to the public EIP of that instance.
I've checked the DNS records with nslookup and they look ok.
I can access the subdomain web server from the browser using its public IP address.

But if I try to access using the domain name, the browser redirects the request to the parent domain (http://sub.example.com -> http://example.com). I'm using Nginx as a reverse proxy & NodeJs as a backend server.

What do I need to do to make it work?

Edit
I'm able to access it if I use the www. prefix (www.sub.example.com). But without the "www" the browser just redirects me to the parent domain..

nginx.conf

user nginx;

worker_processes auto;
error_log /var/log/nginx/error.log;
pid /run/nginx.pid;
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;
    tcp_nodelay         on;
    keepalive_timeout   65;
    types_hash_max_size 4096;

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

    include /etc/nginx/conf.d/*.conf;

    server {
        listen 80;
        server_name sub.example.com www.sub.example.com;

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

        # Redirect all HTTP request to the node.js
        location / {
            proxy_redirect off;
            proxy_pass "http://127.0.0.1:5000";
            proxy_http_version 1.1;
            proxy_set_header Upgrade $http_upgrade;
            proxy_set_header Connection 'upgrade';
            proxy_set_header Host $host;
            proxy_cache_bypass $http_upgrade;
        }
    }
}

CodePudding user response：

The problem was in the dns resolver cache. It has cached obsolete A-records that point to old IPs. After the dns cache has been updated the problem was gone.

Thank you @maslick for your replies.

CodePudding user response：

Create two type "A" DNS records in Route53 (xxx.yyy.zzz.aaa is the public IP address of your EC2 instance, e.g. 18.185.121.30):

sub.example.com -> xxx.yyy.zzz.aaa
www.sub.example.com -> xxx.yyy.zzz.aaa

Use the standard nginx configuration (do not specify any DNS name in server_name - use the default value instead i.e. server_name _;):

user nginx;

worker_processes auto;
error_log /var/log/nginx/error.log;
pid /run/nginx.pid;
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;
    tcp_nodelay         on;
    keepalive_timeout   65;
    types_hash_max_size 4096;

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

    include /etc/nginx/conf.d/*.conf;

    server {
        listen 80;
        server_name _;

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

        # Redirect all HTTP request to the node.js
        location / {
            proxy_redirect off;
            proxy_pass "http://127.0.0.1:5000";
            proxy_http_version 1.1;
            proxy_set_header Upgrade $http_upgrade;
            proxy_set_header Connection 'upgrade';
            proxy_set_header Host $host;
            proxy_cache_bypass $http_upgrade;
        }
    }
}

Both the client (browser) and server (nginx) might be caching responses. Use your browser's Incognito mode or curl to test:

curl -I -H "Cache-Control: no-cache" http://sub.example.com

Be patient. DNS records require some time (time to live or TTL) to propagate across the globe. You can reduce TTL in Route53 and wait less.
To debug DNS issues, use this Linux command:

dig -t a sub.example.com

I also like this web-service which can help you track DNS propagation globally.

UPDATE: here's the example node.js web server I'm running on port 5000:

var http = require('http');

var server = http.createServer(function (req, res) {
  if (req.url == '/') {
    res.writeHead(200, { 'Content-Type': 'text/html' });
    res.write('<html><body><p>This is home Page.</p></body></html>');
    res.end();
  }
});

server.listen(5000);
console.log('Node.js web server at port 5000 is running..')