DevOps Training Material

Docker containers deep dive

docker container run -it <image_name> <program_to_start> creates and starts a container from an image specified.
It additinaly pulls an image if it is locally not available
docker run -it <image_name> also works without explicit container keyword, but it considers a default program_to_start aka entrypoint or cmd is already defined in Dockerfile of the specified image (otherwise container is created but in exited state)
docker run -it starts the container, attaches your terminal shell’s I/O to Containers shell’s I/O.

Observe in the above example that one process is running i.e. sh.
microservices architecture reccomends to run a container limited to one process implementing one service, however docker container supports multiple processes to run inside a container.
docker container ls OR docker ps shows active containers, docker ps -a Includes exited containers too

If you are into a container on the same terminal you can press Ctrl+P+Q to gracefully come out of the container session without existing it.
Lets start multiple containers from the same image. docker run -d will start a container in detached mode.

You can stop a container docker container stop <container_name> or docker container stop <container_id> You can use shorthand to provide the ID value only to its uniquness

docker container stop and docker stop is same. container keyword is almost reduntant since docker is a container in itself ;)
docker rm <container_id> will remove it and docker start <container_id> will start an exited container.
Stop and Start a container will persist any data kept in container. however, it is not reccomended to keep any data in a container.

if you want to access a running container us docker exec -it <container_id or name> <program_to_start>

You can also start a container assigning it a name.
Lets quickly run an nginx container with an assigned name and access it via a custom port

Lets try and remove all containers docker container rm $(docker container ls -aq) -f
docker help shows q in ls -aq is an option of quite which shows only container IDs and -f to force and remove running containers too