Mastering Docker CLI and Dockerfile: A Comprehensive Guide
Soumyadip Chatterjee
Multi-Cloud Strategist | OCI DevOps Engineer | GenAI Aspired | Ex-TCS | Terraform ??? | Docker ?? | Kubernetes ?? | Snowflake?? | Argo CD ?? | Helm ?? | GitLab ?? | Certified: 2x AWS ??, 1x OCI ??, 1x Commvault | 1xGCP
Table of Contents
Docker is a tool designed to make it easier to create, deploy, and run applications by using containers.
Why docker?
Docker is useful to automate the deployment of applications inside a software containers, which makes the applications easy to ship and run virtually anywhere (i.e, platform independent). The Docker container processes run on the host kernel, unlike VM which runs processes in guest kernel.
Installation
The docker desktop downloads are available for windows, mac and linux distributions.
Windows
It supports for Windows 10 64-bit: Home, Pro, Enterprise, or Education, version 1903 (Build 18362 or higher). You need to follow the below steps for installation.
Mac
Linux
You can install from a package easily
Registries and Repositories
Registry:
Docker Registry is a service that stores your docker images. It could be hosted by a third party, as public or private registry. Some of the examples are,
Repository:
A Docker Repository is a collection of related images with same name which have different tags. These tags are an alphanumeric identifiers(like 1.0 or latest) attached to images within a repository.
For example, if you want to pull golang image using docker pull golang:latest command, it will download the image tagged latest within the golang repository from the Docker Hub registry. The tags appeared on dockerhub as below,
Login
Login to a registry
> docker login [OPTIONS] [SERVER]
[OPTIONS]:
-u/--username username
-p/--password password
Example:
1. docker login localhost:8080 // Login to a registry on your localhost
2. docker login
Logout
Logout from a registry
> docker logout [SERVER]
Example:
docker logout localhost:8080 // Logout from a registry on your localhost
Search image
Search for an image in registry
docker search [OPTIONS] TERM
Example:
docker search golang
docker search --filter stars=3 --no-trunc golang
Pull image
This command pulls an image or a repository from a registry to local machine
docker image pull [OPTIONS] NAME[:TAG|@DIGEST]
Example:
docker image pull golang:latest
Push image
This command pushes an image to the registry from local machine.
docker image push [OPTIONS] NAME[:TAG]
docker image push golang:latest
Create,Run,Update and Delete containers
Create
Create a new container
docker container create [OPTIONS] IMAGE [COMMAND] [ARG...]
Example:
docker container create -t -i sudheerj/golang --name golang
Rename
Rename a container
docker container rename CONTAINER NEW_NAME
Example:
docker container rename golang golanguage
docker container rename golanguage golang
Run
docker container run [OPTIONS] IMAGE [COMMAND] [ARG...]
Example:
docker container run -it --name golang -d sudheerj/golang
You can also run a command inside container
docker exec [OPTIONS] CONTAINER COMMAND [ARG...]
Example:
docker exec -it golang sh // Or use bash command if sh is failed
Update
Update configuration of one or more containers
docker container update [OPTIONS] CONTAINER [CONTAINER...]
Example:
docker container update --memory "1g" --cpuset-cpu "1" golang // update the golang to use 1g of memory and only use cpu core 1
Remove
Remove one or more containers
docker container rm [OPTIONS] CONTAINER [CONTAINER...]
Example:
docker container rm golang
docker rm $(docker ps -q -f status=exited) // Remove all the stopped containers
Start and stop containers
Start
Start one or more stopped containers
docker container start [OPTIONS] CONTAINER [CONTAINER...]
Example:
docker container start golang
Stop
Stop one or more running containers
docker container stop [OPTIONS] CONTAINER [CONTAINER...]
Example:
docker container stop golang
docker stop $(docker ps -a -q) // To stop all the containers
Restart
Restart one or more containers and processes running inside the container/containers.
docker container restart [OPTIONS] CONTAINER [CONTAINER...]
Example:
docker container restart golang
Pause
Pause all processes within one or more containers
docker container pause CONTAINER [CONTAINER...]
Example:
docker container pause golang
Unpause/Resume
Unpause all processes within one or more containers
docker container unpause CONTAINER [CONTAINER...]
Example:
docker container unpause golang
Kill
Kill one or more running containers
docker container kill [OPTIONS] CONTAINER [CONTAINER...]
Example:
docker container kill golang
Wait
Block until one or more containers stop and print their exit codes after that
docker container wait CONTAINER [CONTAINER...]
Example:
docker container wait golang
Networks
Docker provides network commands connect containers to each other and to other non-Docker workloads. The usage of network commands would be docker network COMMAND
List networks
List down available networks
docker network ls
Connect a container to network
You can connect a container by name or by ID to any network. Once it connected, the container can communicate with other containers in the same network.
docker network connect [OPTIONS] NETWORK CONTAINER
Example:
docker network connect multi-host-network container1
Disconnect a container from a network
You can disconnect a container by name or by ID from any network.
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docker network disconnect [OPTIONS] NETWORK CONTAINER
Example:
docker network disconnect multi-host-network container1
Remove one or more networks
Removes one or more networks by name or identifier. Remember, you must first disconnect any containers connected to it before removing it.
docker network rm NETWORK [NETWORK...]
Example:
docker network rm my-network
Create network
It is possible to create a network in Docker before launching containers
docker network create [OPTIONS] NETWORK
Example:
sudo docker network create –-driver bridge some_network
The above command will output the long ID for the new network.
Inspect network
You can see more details on the network associated with Docker using network inspect command.
docker network inspect networkname
Example:
docker network inspect bridge
Additional Docker CLI commands for Networking :-
$ docker network ls
$ docker network ls | grep "bridge"
$ docker network rm $(docker network ls | grep "bridge" | awk '/ / { print $1 }')
$(docker network ls | grep "bridge" | awk '/ / { print $1 }')
Types of Networking:-
Bridge Network
$ docker network create -d bridge my-net
$ docker run --network=my-net -itd --name=container1 busybox
User Defined Bridge Network
$ docker network create --driver=bridge --subnet=172.25.0.0/16 my-bridge-net
$ docker run --network=my-bridge-net -itd --name=container2 busybox
Host Network
$ docker run --network=host -itd --name=container3 busybox
Overlay Network
$ docker swarm init
$ docker network create -d overlay my-overlay-net
$ docker service create --name my-service --network my-overlay-net --replicas 3 busybox ping docker.com
Macvlan/Ipvlan Network
$ docker network create -d macvlan --subnet=192.168.1.0/24 --gateway=192.168.1.1 -o parent=eth0 my-macvlan-net
$ docker run --network=my-macvlan-net -itd --name=container4 busybox
Cleanup commands
You may need to cleanup resources (containers, volumes, images, networks) regularly.
Remove all unused resources
docker system prune
Images
$ docker images
$ docker rmi $(docker images --filter "dangling=true" -q --no-trunc)
$ docker images | grep "none"
$ docker rmi $(docker images | grep "none" | awk '/ / { print $3 }')
Containers
$ docker ps
$ docker ps -a
$ docker rm $(docker ps -qa --no-trunc --filter "status=exited")
Volumes
$ docker volume rm $(docker volume ls -qf dangling=true)
$ docker volume ls -qf dangling=true | xargs -r docker volume rm
Utility commands
Docker Hub
Docker Hub is a cloud-based repository provided by Docker to test, store and distribute container images which can be accessed either privately or publicly.
From
It initializes a new image and sets the Base Image for subsequent instructions. It must be a first non-comment instruction in the Dockerfile.
FROM <image>
FROM <image>:<tag>
FROM <image>@<digest>
Note: Both tag and digest are optional. If you omit either of them, the builder assumes a latest by default.
Dockerfile
Dockerfile is a text document that contains set of commands and instructions which will be executed in a sequence in the docker environment for building a new docker image.
FROM
This command Sets the Base Image for subsequent instructions
FROM <image>
FROM <image>:<tag>
FROM <image>@<digest>
Example:
FROM ubuntu:18.04
RUN
RUN instruction allows you to install your application and packages required for it. It executes any commands on top of the current image and creates a new layer by committing the results. It is quite common to have multiple RUN instructions in a Dockerfile.
It has two forms
RUN npm start
RUN [ "npm", "start" ]
CMD and ENTRYPOINT are two Dockerfile instructions that work together to define the command that runs when your container starts. ENTRYPOINT sets the process to run, while CMD supplies default arguments to that process.
Here’s an example: suppose you have a Dockerfile that looks like this:
FROM ubuntu
ENTRYPOINT ["/usr/bin/my-app"]
CMD ["help"]
In this example, the ENTRYPOINT instruction sets the process to run, which is /usr/bin/my-app. The CMD instruction sets the default arguments that are passed to the ENTRYPOINT process, which is help. When you run a container from this image, the command that will be executed is /usr/bin/my-app help.
You can override the CMD instruction by passing arguments to the docker run command. For example, if you run the following command:
$ docker run my-image:latest version
The command that will be executed is /usr/bin/my-app versionThe path must be relative to the source directory that is being built. Whereas is an absolute path, or a path relative to WORKDIR.
You can place these components in a Dockerfile in any order you like. Here’s an example Dockerfile that uses all of these components:
FROM ubuntu
COPY test.txt /absoluteDir/
ADD source.file.tar.gz /temp
ENV name="John Doe" age=40
EXPOSE 80
This Dockerfile copies test.txt to the /absoluteDir/ directory in the container using COPY, and extracts source.file.tar.gz to the /temp directory in the container using ADD. It sets the environment variables name and age to the values "John Doe" and 40, respectively, using ENV. Finally, it informs Docker that the container listens on port 80 using EXPOSE.
Multiple Ports can be also exposed as follows :-
EXPOSE <port> [<port>/<protocol>...]
Example:
EXPOSE 80/udp
EXPOSE 80/tcp
But if you want to bind the port of the container with the host machine on which the container is running, use -p option of docker run command.
docker run -p <HOST_PORT>:<CONTAINER:PORT> IMAGE_NAME
Example:
docker run -p 80:80/udp myDocker
You can place these components in a Dockerfile in any order you like. Here’s an example Dockerfile that uses all of these components:
FROM ubuntu
WORKDIR /app
LABEL version="1.0"
RUN mkdir /test
VOLUME /test
This Dockerfile sets the working directory to /app using WORKDIR, adds a label to the image with the version number 1.0 using LABEL, creates a directory named /test using RUN, and creates a volume named /test using VOLUME.
Docker Compose
Docker compose(or compose) is a tool for defining and running multi-container Docker applications.
Docker Swarm
Docker Swarm(or swarm) is an open-source tool used to cluster and orchestrate Docker containers.
The docker exec command is used to run commands inside a running Docker container. The -it flag is used to open an interactive terminal session inside the container. Here are some examples of using docker exec with -it:
$ docker exec -it container_name /bin/bash
$ docker exec -it container_name command
Here’s an example of using docker exec with -it to run a command inside a running container:
$ docker exec -it container_name ls -l
To ping from one container to another container, you can use the ping command followed by the IP address or hostname of the target container. Here is an example command:
$ docker exec -it container1 ping container2
Docker volumes and storage are essential for persisting data generated by and used by Docker containers. Volumes are the preferred mechanism for persisting data, while bind mounts are dependent on the directory structure and OS of the host machine.
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