Hi there @raj350,

If you run those 2 commands:

 docker run -d --name flask1 -p 8080:80 flask1
 docker build flask2:latest . 
 docker run -d --name flask2 -p 8081:80 flask2

Then this means that your Flask containers are running on port 8080 and 8081. If you run docker ps do you see the containers running?

If the containers are not running you could check your logs with the following command:

docker logs -f docker_container_id

Also if you run netstat -plant do you see the docker containers listening on the 8080 and 8081 ports?

If your containers are listening on those 2 ports but if you are still unable to access them via your browser, make sure that the two ports are open via your firewall.

Regarding the Nginx setup, if you have your containers listening on port 8080 and 8081, then you should set your Nginx service on port 80 and the proxy pass to 8080 and 8081, this would be useful if you have domain names and you could proxy the traffic depending on the domain name. So it would look something like this:

upstream docker-flask1  {
  server flask1:8080;
}

upstream docker-flask2 {
  server flask2:8081;
}

server {
  listen 80;

  sever_name app1.yourdomain.com;

  location /test1 {
    proxy_pass http://docker-flask1;
    proxy_redirect  off;
  }
}

server {
  listen 80; 

  server_name app2.yourdomain.com;

  location /test2 {
    proxy_pass http://docker-flask2;
    proxy_redirect off;
  }

}

Let me know if you have any questions!
Regards,
Bobb