Docker Basics

docker version

Verifies that the docker client is running on your machine and returns the version #

Docker run

docker run hello-world

• Docker client contacted the Docker server.
• Server looks for image in it's image cache and does not find it, so it pulls the "hello-world" image from Docker Hub.
• Server created a new container from that image and runs the image's default startup command - in this case calling some sort of hello world executable.
• Server streamed the output to Docker client, which sent it to terminal.
• The hello world executable finishes its task and since there is nothing left to do, it exits, which, in turn causes the container to exit - but leaves it in the server's container cache to start again later, if desired.

docker run busybox ls

• Download the busybox image if not in the image cache.
• Create a container from image and override the default startup command with ls, the command to list files in the container.
• Stream results to the terminal.
• Since ls completes, the process exits and the container exits

docker run is a combination of

docker create busybox echo Hello There
docker start -a <containerid>

Where the -a option (or --attach) makes the container attach its stdout/stderr output to the terminal

Docker ps

docker ps

List all the running containers on the docker server

docker ps --all

or

docker ps -a

List all the containers, including ones that have exited

docker prune

Removes all stopped images and dangling images from server.

Docker logs

This command allows you to retrieve the console logs from a container. For example:

$ docker create busybox echo hi there
2905656c9b592a90e94a2ef0507dbaf27e22aba53500319ec9554a7dd7962558

darra@Lenovo MINGW64 /c/git/hackforla/tdm-calculator (531-jwt-cookie-expires)
$ docker start 2905
2905

darra@Lenovo MINGW64 /c/git/hackforla/tdm-calculator (531-jwt-cookie-expires)
$ docker logs 2905
hi there

Docker stop / Docker kill

docker stop <containerid>
docker kill <containerid>

stop' will issue a SGITERM message to the process, possibly giving it a chance to shutdown gracefully. However, if the process does not shut down within about 10 seconds, it will automatically kill the process.kill` is more violent.

Multi-command containers

Want to run a client and server in the same container? Need to run an addition command inside a running container

docker run redis

docker exec -it <containerid> redis-cli

exec runs a command in <containerid>. The -i (or --interactive) option keeps stdin open, and the -t (or --tty) allocates a pseudo-TTY - together they allow you to interact with the container.

docker exec -it <containerid> sh

runs a command shell sh in the container. Some containers will have other shells such as bash or zsh.

Starting a shell

docker run -it busybox sh

This runs the shell as the primary process, which is sometimes useful. More commonly, you will probably run some other main process, such as a server and exec as shell as described earlier.

Notes

Different docker containers do not, by default share any disk space and are completely isolated.

Docker Volumes

Git Bash on Windows

MSYS_NO_PATHCONV=1 docker run -p 8080:3000 -v $(pwd):/var/www -w /var/www node npm start

There should be a way to use escape characters for the volume and workdir related strings, but I haven't figured it out.

Docker custom images

We can create our own images by creating a Dockerfile, then running docker build to process the Dockerfile to start with a base image and layer other stuff on top of it ot build our container and specify a startup command for our image.

docker build .

. is the build context, i.e., the directory from which the docker cli should run.

We can give the new image a name by tagging it:

docker build -t tdmcalc/tdmweb:0.0.1 .

Then we can run the image by:

docker run tdmcalc/tdmweb:0.0.1

You can manually take a running container and create an image out of it

docker commit -c 'CMD ["redis-server"]'  <containerid>

This is generally not something you would do, but demonstrates what happens when a dockerfile is processed.

Dockerfile to build a custom image

docker-compose up -d

runs docker-compose.yml to startup multiple containers. The -d option starts them in the background.

docker-compose down

stops all the docker-compose referenced containers.