Docker Container

When a Docker image is run, it creates a Docker container, which is a running instance of the image. Multiple containers can be created from the same image, each with its own isolated environment and resources, making it easy to run multiple instances of an application on the same machine.

A container is an isolated place where an application runs without affecting the rest of the system and without the system impacting the application. Therefore containers are well-suited for securely running software like databases or web applications that need access to sensitive resources without giving access to every user on the system.

State

Docker containers have six states which represent a piece of valuable information about the container:

1. Created
2. Running
3. Restarting
4. Paused
5. Exited
6. Dead

Create

Docker assign the Create stater for containers when it is just created and never started

Hence, no CPU or memory is used by the containers in this state.

So it will be after creating a container from the docker image by running

docker create 
docker container ls -a

the first command will create a container, and the second will list the container with the state Created.

Running

You can run a container that is already created or exited by running

docker start 

And you can join an already running container by the attach command

docker attach 

Restarting

This is a state for the container when it is restarting, you can achieve this state when you restart a container by

docker restart 

Paused

You can pause an already-running container

Hence, The paused container reserves the same memory but it is not consuming CPU

docker pause 

Exited

This state can occur in two cases:

1. if the container has been stopped by the docker

   docker stop 

2. There is an exception happened in the container or the process execution inside the container has been done.

Dead

The dead state of a Docker container means that the container is non-functioning. This state is achieved when we try to remove the container, but it cannot be removed because some resources are still in use by an external process. Hence, the container is moved to the dead state.

Containers in a dead state cannot be restarted. and they do not consume any memory or CPU.

Generate Container

To generate a container to work with Docker has pre-steps to do so:

1. You have to have an Image
2. Run the image to have a container from it (you can consider it as an instance of the image)

We will assume here that you already have an Image generated container from it, and we will discuss the image creation in the next topic, but for now, assume that we have a docker image.

List image

so we can list the docker images by:

docker image ls

Create a container

then create a container from the image

docker create 

List containers

After this command, you will have a new container, and you can list the containers by

docker container ls -a

this command will list all containers (the running and the stopped containers), and list only the running containers

docker container ls

Start container

To start an ideal container

docker run 

To join to a running container

docker attach 

To get stdin, stdout and tty with container

docker run -i -t 

To share folder between the host and the container

docker run -v :

To install or run command in container

docker exec -it [container] pip3 install pandas

this will install pandas for python3 for example.

Stop container

To stop already running container

docker stop 

Now you have enough information to understand the docker container, we will cover more container commands and specs in the next topics, so see you around

Delete containers

To delete container

docker rm 

To delete all containers

docker rm $(docker ps -a -q)

Containers inspect

Get information about the container

docker inspect 

To get the container IP for example

docker inspect  | grep "IPAddress"

Containers exec

To run command in running container

docker exec  

To access the docker container

docker exec -it  /bin/bash

Containers Rename

To rename container

docker rename  

Create Image from Container

To make an image from existed container

docker commit  

Add volume to container

To make a shared volume between the host and docker image

docker run -dit --name  -v : 

Git logs of the container

To get the latest logs of the running container

docker logs 

You can limit the logs for specific lines by -n and the number of lines, or --tail

docker logs -n 10 

You can keep track the logs by -f, --follow

docker logs -n 10 -f