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My Dockerfile contains this:
EXPOSE 80
Yet, if I run the image with -P I can't connect to it. Running with -p 80:80 works fine.
danny@linux:~$ sudo docker run -d -P dart-test
b3277a5483531f6dc23a1c807cf895103fd5333b603c1b4a352e07c9721f1a48
# Can't connect here
danny@linux:~$ curl http://localhost/
curl: (7) Failed to connect to localhost port 80: Connection refused
danny@linux:~$ sudo docker stop b3277
b3277
danny@linux:~$ sudo docker run -d -p 80:80 dart-test
dfe68699bfb33ce33e8e6e1953ac828b9d31209988df64e2627d9228758438ba
# Connects fine here
danny@linux:~$ curl http://localhost/
Hello, world!
danny@linux:~$
979
By default, when you create or run a container using docker create or docker run , it does not publish any of its ports to the outside world. To make a port available to services outside of Docker, or to Docker containers which are not connected to the container's network, use the --publish or -p flag.
To publish a port for our container, we'll use the --publish flag ( -p for short) on the docker run command. The format of the --publish command is [host_port]:[container_port] . So if we wanted to expose port 8080 inside the container to port 3000 outside the container, we would pass 3000:8080 to the --publish flag.
By default, the httpd server listens on port 80. It's not mandatory to perform port mapping for all Docker containers. Often, we will avoid opening host ports in order to keep the services of the container private or only visible to sibling containers in the same Docker network.
When you use -P, docker will bind the exposed port to a random high port from the range 49153 to 65535 on the docker host. To determine the actual port, you'll need to run
docker port <CONTAINER> 80
When you use -p 80:80, you specifically bind the exposed port to the host's port 80.
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