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Ports mapping , volumes,…

Ports mapping

Run custom static site image

docker run --name static-site -e AUTHOR="Your Name" -d -P dockersamples/static-site

In the above command:

  • -d will create a container with the process detached from our terminal
  • -P will publish all the exposed container ports to random ports on the Docker host
  • -e is how you pass environment variables to the container
  • --name allows you to specify a container name
  • AUTHOR is the environment variable name and Your Name is the value that you can pass

Now you can see the ports by running the docker port command.

$ docker port static-site
443/tcp -> 0.0.0.0:32768
80/tcp -> 0.0.0.0:32769

You can open http://localhost:[YOUR_PORT_FOR 80/tcp]. For our example this is http://localhost:32769.

Clean up the containers since you won't be using them anymore.

$ docker stop static-site
$ docker rm static-site

(shortcut : docker rm -f static-site )

If I prefer mapping the port on a specific one I can do it with option -p.

First of all, stop the container docker stop static-site and now map port 80 of the container to 8888 port of the host machine.

docker run --name static-site -e AUTHOR="Your Name" -d -p 8888:80 dockersamples/static-site

Options:

  • --publish , -p Publish a container's port(s) to the host

Attach port to an existing container

docker stop <running-container-name>
docker run -p <new-port-mapping> <container-name-from-step-1>

Volumes

Basically, volumes are special directories in containers "mounted" from somewhere.

Docker volumes are useful for living some files out of docker or sharing a directory/file between multiple containers/hosts.

You can use local storage or a remote storage (plugins or custom).

Volumes can be defined directly in Dockerfie

VOLUME /uploads

or from command-line

docker run -d -v /uploads myapp

  • When you docker commit, the content of volumes is not brought into the resulting image.

  • If a RUN instruction in a Dockerfile changes the content of a volume, those changes are neither recorded.

  • If a container is started with the --read-only flag, the volume still be writable (unless the volume is a read-only volume).

  • You can share volumes between containers using --volumes-from flag for docker run.

Example Let's start a Tomcat container:

$ docker run --name webapp -d -p 8080:8080 -v /usr/local/tomcat/logs tomcat

Now, start an alpine container accessing the same volume:

$ docker run --volumes-from webapp alpine sh -c "tail -f /usr/local/tomcat/logs/*"

Then, from another window, send requests to our Tomcat container:

$ curl localhost:8080

To list volumes use docker volume ls.

Naming volumes

Volumes can be created without a container, then used in multiple containers.

$ docker volume create mycustomwebsite

Volumes are not anchored to a specific path.

Let's start a web server using the two previous volumes.

$ docker run -d -p 1234:80 -v mycustomwebsite:/usr/share/nginx/html nginx

check using curl localhost:1234.

Let's start another container using the html volume.

$ docker run -v mycustomwebsite:/html --workdir /html -ti alpine vi index.html

Edit the page, save and exit. Run curl localhost:1234 again to see your changes.

Volumes typical usage: databases

PostgreSQL data

$ docker volume create mydata
$ docker run -it --rm \
    --name mydb \
    -v mydata:/var/lib/postgresql/data \
    -e POSTGRES_PASSWORD=mysecretpassword \
    postgres:13

$ docker exec -ti mydb psql -U postgres
postgres=# CREATE DATABASE mydb;
postgres=# \q