running docker gives Ports are not available error

Question

docker run --rm -it -p 8080:80 mcr.microsoft.com/dotnet/core/runtime:3.1
docker run --rm -it -p 8080:80 mcr.microsoft.com/dotnet/core/sdk:3.1
docker run --rm -it -p 8080:80 mcr.microsoft.com/dotnet/core/aspnet:3.1

When I run any of the above docker commands to create a container, I get the following error. And I get this for both for linux as well as windows.

C:\Program Files\Docker\Docker\resources\bin\docker.exe: Error response from daemon: Ports are not available: listen tcp 0.0.0.0:8080: bind: An attempt was made to access a socket in a way forbidden by its access permissions. time="2020-03-24T17:20:44+05:30" level=error msg="error waiting for container: context canceled"

I tried the suggestion given in this SO ans to find the process Id and kill it.

Further I got the process hacker as suggested here to observe whats that process. Looks like its a system process.

Can anybody suggest what can be done?

Answer 1

-p 8080:80 says "forward port 8080 on the host to port 80 in the container". Port 80 is determined by the container image. Port 8080 is arbitrary—it's a port you're choosing.

So instead do -p 8081:80, and now you point your browser at localhost:8081 instead of localhost:8080.

If that doesn't work then maybe it's your firewall?

(See https://pythonspeed.com/articles/docker-connection-refused/ for diagrams of how port forwarding works).

Answer 2

You assign the same host port 8080 multiple times, which is not allowed - on any operating system.

After running this command

docker run --rm -it -p 8080:80 mcr.microsoft.com/dotnet/core/runtime:3.1

the first container gets immediately the port 8080 assigned on the host machine, what we can also see in the console screenshot that you provided. And others fail, because they simply don't get the port they want. So that all containers can be started, you should use a different port for each container, a la

docker run --rm -it -p 8080:80 mcr.microsoft.com/dotnet/core/runtime:3.1
docker run --rm -it -p 8081:80 mcr.microsoft.com/dotnet/core/sdk:3.1
docker run --rm -it -p 8082:80 mcr.microsoft.com/dotnet/core/aspnet:3.1

You should then be able to access those containers via the respective ports 8080, 8081, and 8082 (on localhost or local network IP of ur machine, e.g. 192.168.1.20).