localhost not working docker windows 10

Question

I am using VS2017 docker support. VS created DockerFile for me and when I build docker-compose file, it creates the container and runs the app on 172.x.x.x IP address. But I

Answer 1

Most likely a different application already runs at port 80. You'll have to forward your web site to a different port, eg:

docker run -d -p 5000:80 --name myapp myasp

And point your browser to http://localhost:5000.

When you start a container you specify which inner ports will be exposed as ports on the host through the -p option. -p 80:80 exposes the inner port 80 used by web sites to the host's port 80.

Docker won't complain though if another application already listens at port 80, like IIS, another web application or any tool with a web interface that runs on 80 by default.

The solution is to:

1. Make sure nothing else runs on port 80 or
2. Forward to a different port.

Forwarding to a different port is a lot easier.

To ensure that you can connect to a port, use the telnet command, eg :

telnet localhost 5000

If you get a blank window immediatelly, it means a server is up and running on this port. If you get a message and timeout after a while, it means nobody is running. You anc use this both to check for free ports and ensure you can connect to your container web app.

PS I run into this just a week ago, as I was trying to set up a SQL Server container for tests. I run 1 default and 2 named instances already, and docker didn't complain at all when I tried to create the container. Took me a while to realize what was wrong.