Docker’s Reference: The Ultimate Guide

Image from hub.docker.com

This article is intended to be a brief description of the most used commands in Docker and understand the different concepts.

What is Docker?

Docker is a tool that enables you to quickly create, test, and deploy containerized applications.

What is a container?

Containers are running instances of an image. They are the ones who run things, the ones who will run our application. The container concept is like restoring a virtual machine from a snapshot.
From a single image, we can run multiple containers.

What is an image?

We can say that an image is a package that contains everything necessary for an application/service to run.

Images are used to create containers, and they never change.
There are many public images with basic elements like Java, Ubuntu, Apache, Mongo … etc, that can be downloaded and used. Normally when you create images, we start from a parent image to which we add things.

What is a volume?

Volumes in Docker is the simple and predefined way to store all files in a container.

It is not a good practice to save persistent data inside a Docker container. That’s what volumes are for, outside of containers. So we can create and delete containers without worrying about the data being deleted.

What is a network?

Networks in Docker will allow you to relate different containers to each other or to isolate them completely.

The most used commands are:

Know all the commands to use about an image:

docker image --help

Download an image. If you want to download a specific version, you need to add the image version if not, you just need to indicate which image you want to download:

docker pull mongo -> latest mongo version
docker pull mongo:3.6 -> 3.6 mongo version

Build your own image from a previously created Dockerfile (Let’s assume that our Dockerfile will display a mongo image):

docker build --tag mongo .

Find all images that start with a word or character. For example “mongo”.

docker images | grep mongo

Delete the image, here we have 2 options:

docker rmi mongo -> Delete the image with "mongo" name.
docker rmi [IMAGE_ID] --> Delete the image with "image_id" image.

To know all the commands to use about a container:

docker container --help

Create a simple container (where -d → Run the container in daemon mode):

docker run -d mongo

Create a simple container where it is indicated container name:

docker run -d --name containerName mongo

Create a simple container where it is indicated the port:

docker run -d -p internPort:externalPort --name containerName mongo

Add environment variables by command line to create a simple container (where -e → Run the container with environment variables):

docker run -d -e "test=123" --name containerName mongo

Get all the containers with the status “run”, type the command:

docker ps

Get all containers (actives and inactive):

docker ps -a

Remove the containers, there are different options:

1. Remove a container: docker rm -f containerName
2. Remove some containers: docker rm -f containerName containerName1
3. Remove all containers: docker rm -fv $(docker ps -aq)

Rename the container:

docker rename containerName containerNewName

Stop the container:

docker stop containerName

Stop all containers (active and inactive):

docker stop $(docker ps -aq)

Start a container:

docker start containerName

Restart a container:

docker restart containerName

Know the resources used by a container:

docker stats containerName

Perform actions to limit and increase the resources of a container, we can use these commands:

• Limit or increase the memory that a container can use (Where -m → It means memory limit):

docker run -d -m "limitMemory" --name containerName mongo

• How many CPUs does it have in our machine?:

grep "model name" /proc/cpuinfo | wc -l

• Limit or increase the number of CPUs to use:

docker run -d --cpuset-cpus 0-1 --name containerName mongo

Inspect a container, it means to get all information about the container:

docker inspect containerName

Copy files to a container:

• From our local to the container. Copy indext.html file from our local to /tmp/ folder in Apache container:

docker cp index.html apache:/tmp/

• From the container to our local. Copy the file test.log from the container to the current directory of our machine:

docker cp apache:/tmp/test.log .

Know all the commands to use about volumes:

docker volumes --help

Get all volumes created:

docker volume ls

Create a simple volume:

docker volume create volumeName

Delete created volumes:

docker volume rm volumeName

Display detailed information on one or more volumes:

docker volume inspect volumeName

Remove dangling volumes. It means volumes that don’t reference any container:

docker volume ls -f dangling = true | xargs docker volume rm

Know all the commands to use about the network:

docker network --help

Get all network created:

docker network ls

Get specific information from a network:

docker inspect networkName

Filter by a specific network:

docker network ls | grep [NETWORK_TYPE]

Create a simple network:

docker network create networkName

Create a specific network (where “bridge” is the network):

docker network create -d bridge --subnet 172.124.10.0/24 --gateway 172.124.10.1 networkName2

Create a container connected to a specific network:

docker run -d --network networkName2 mongo

How to connect two containers on the same network?

1. docker run -d --network networkName2 --name containerName mongo
2. docker run -d --network networkName2 --name containerName2 mongo

Delete network:

1. Before deleting a network, make sure that no container is using it. This command can help you:

docker rm -fv $(docker ps -aq)

2. Delete the network:

docker network rm networkName

And that’s it!!, I hope it was helpful to clarify concepts -:-)