Managing Docker Containers

1. Container Commands

1. Create a new container using the below command

sudo docker run -it ubuntu /bin/bash

The "docker run" command provides all launching capabilities for docker to create a container. We use docker run to create new containers.
-i: open STDIN from the container
-t: tells docker to assign a pseudo-tty to the container
-it : provides an interactive shell
ubuntu: ubuntu is an image and also called as "stock image" or "base image". This image will be downloaded from Docker hub when we run 'docker run' command first time
/bin/bash: 'shell program' that will be installed in the terminal

2. Inspect the new container

Let's believe that it's a separate machine by using the below commands

hostname
cat /etc/hosts
hostname -i
ps -ef

3. SSH setup for containers

Setup SSH in the containers so that they can communicate with each other

Create two containers having IP addresses - 172.17.0.2, 172.17.0.3
Try to connect to 172.17.0.3 from 172.17.0.2 using the below command. You will get an error.

$ ssh demo@172.17.0.3 (you won't be able to connect by default)
Install ssh server

$ apt-get update

$ apt-get install openssh-server
Start the server

$ service ssh start (status/stop/restart)
Create a user and set up a password

$ useradd -m -d /home/demo -s /bin/bash demo

$ passwd demo
Connect to the container using ssh from 172.17.0.2 or any other machine.

$ ssh demo@172.17.0.3
Enable root user over ssh

Add the below line under "# Authentication:" in "/etc/ssh/sshd_config" PermitRootLogin yes

4. Shutdown a container

"exit" to stop the container

5. Log in to a stopped container

$docker start

$docker attach

6. List all containers(stopped and running)

$ docker container ls -a

$ docker ps -a

7. List given no. of containers

$ docker ps -a -n1

8. List running containers only

$ docker container ls

$ docker ps

9. List Stopped containers only

$ docker container ls -f status=exited (Where Status can be exited/running)

The "docker container ls" command output shows:

- Image name from which container is created

- ID - the container can be identified using short UUID, longer UUID Or name.

- Status of the container (Up / Exited)

- Name of the container

10. Show the last container which you have created (stopped/running)

$ docker container ls -l

11. Naming the container

$ docker run --name demo -it ubuntu /bin/bash

Note: Two containers can't have the same name.

12. Rename a container

$ docker rename container_name_1 container_name_2

13. Deleting a container by giving its name or ID

$ docker rm ID/name

14. Delete all (running/stopped) containers at once

$ docker rm -f $(docker container ls -a -q)

$ docker rm -f $(docker ps -a -q)

15. Delete running containers only

$ docker rm -f $(docker container ls -q)

$ docker rm -f $(docker ps -q)

16. List stopped containers only

$ docker container ls -a -f status=exited

17. Starting a stopped container

$ docker start container_name

18. Attaching to a running container

$ docker attach container_name (OR)

$ docker attach b1b1c8dc1939

19. Run a Linux command remotely in a container Or Get an independent terminal from a container remotely (from the Host)

$ docker exec -it tomcat-server ps -ef

20. Stopping a container from the 'host machine'

$ docker stop container_name(Gracefully stop the container)

$ docker kill container_name(Forcibly stop the container)

21. Inspecting the container's processes from the host machine

$ docker top container_name

22. Show the last 4 containers (stopped/running)

$ docker ps -n4

23. Create a container in a background mode ( without terminal access )

$ docker run -it -d ubuntu /bin/bash

24. Find More About The Container

The 'docker inspect' command interrogates the container and returns complete information about it.

Ex: image name, IP, Memory details, hostname ..etc

Examples:

$ docker inspect container_name

$ docker inspect -f '{{.Config.Hostname}}' container_name

$ docker inspect -f '{{.NetworkSettings.Networks.bridge.IPAddress}}' container_name

Note: use --format (OR) -f

25. List all container names

$ docker inspect --format "{{.Name}}" $(docker ps -a -q) | tr -d '/'

2. STATS:

1. Display usage statistics of a container

$ docker stats --no-stream container_name

$ docker stats --no-stream --all

$ docker stats --no-stream --format {{.MemUsage}} container_name

$ docker stats --no-stream --format {{.CPUPerc}} container_name

2. Allocating memory for a container (below command allocates 1 GB RAM)

$ docker run -it --name container_name -m 1g ubuntu /bin/bash

$ docker run -it --name container_name -m 1024m ubuntu /bin/bash

3. Updating memory of an existing container

$ docker update -m 2024m container_name

4. CPU Allocation

$ docker run -it --cpus="2" --name container_name ubuntu /bin/bash

$ docker update --cpus="2" conatiner_name