Docker
Docker is a tool for developers to create, deploy, and run applications using containers. Containers assist to package the applications, together with all components require such as libraries and other dependencies, and combine together as a single entity so that the application can run on other devices.


Docker Component
Major Docker components/architecture consists of some main components, namely, registry, image, container, daemon, and client.
Registry: This can be called the docker shelf that stores docker images.The Docker registry that we use is called Docker Hub.
Image: Images are a read-only template used to build containers.It can be downloaded from the registry directly or implicitly when starting a container.It can be use to transport n application.
Container:This is the environment that the docker is been run and wrapped.They can only have access to resource that is define in their configuration
Docker daemon: A daemon creates, runs, and monitors containers, along with building and storing images.
Client: Docker client allows users to interact with Docker.It allows image to be pulled directly from docke.A client talks to Docker daemon via HTTP.

Orchestrate
This is the process of managing the life cycle of docker.It is used for automating and controlling the life cycel of docker E.g Kubernetes and docker Swarm.

Commands
To initialize the swarm mode and listen to a specific interface:
Docker swarm init --advertise-addr 10.1.0.2
To join an existing swarm as a manager node:
Docker swarm join --token<manager-token> 10.1.0.2:2377
To join a swarm as a worker node:
Docker swarm join --token<worker-token> 10.1.0.2:2377
To list all nodes in the swarm:

To create a service from an image on the existing port and deploy three instances:
Docker service create --replicas 3 -p 80:80 name -webngix
To list services running in a swarm:
Docker service ls
To scale a service:
Docker service scale web=5
To list the tasks of a service:
Docker service ps web

Build
The build command is used for building images from a Docker file. Let’s now check out some of the essential Docker build commands.
Commands
To build an image from the Docker file and tag it:
Docker build -t app :1.0
To list all the images that are locally stored:
Docker images
To delete an image from the Docker Store:
Docker rmi alpine: 3.4

Run
The run command is used for creating a container from a specified image.
Commands
To create and run a command:
Docker run --name container_name docker_image
Flags used:
-d: To detach a container on start
-rm: To remove a container once it stops
-p: To publish the host IP and the host port to the container port
-v: To define and share the volume across containers
–read-only: To set to the read-only permission
Ship
Docker allows us to transport our application container anywhere, on any platform.
Commands
To pull an image from the registry:
Docker pull alpine:3.4
To retag a local image with a new image name:
Docker tag alpine:3.4 myrepo/ myalpine:3.4
To log in to the registry:
Docker login my.registry.com:8000
To push an image to the registry:
Docker push myrepo/ myalpine:3.4

Clean up
Docker clean up is very importnat so as to free unused resources.
Commands
To clean an unused/dangling image:
Docker image prune
To remove an image that is not used in a container:
Docker image prune -a
To prune the entire system:
Docker system prune
To leave a swarm:
Docker swarm leave
To remove a swarm:
Docker stack rm stack_name
To kill all running containers:
Docker kill $ (docker ps -q)
To delete all stopped containers:
docker rm $(docker ps -a -q)
To delete all images:
docker rmi $(docker images -q)
Services
Let’s now take a sneak peek at the commands used to view the running services, to run the services, to view all service logs, and to scale the services.
Commands
To list all services running in a swarm:
Docker service ls
To see all running services:
Docker stack services stack_name
To see all service logs:
Docker service logs stack_name service_names
To scale a service across qualified nodes:
Docker service scale stack_name_service_name= replicas


Interaction with a Container
Let’s check out how to make an interaction with a container in Docker.
Commands
To run a command in a container:
Docker exe -ti container_name command.sh
To follow container logs:
Docker logs -ft container name
To save a running container as an image:
Docker commit -m “commit message” -a “author” container_name username/image_name: tag

Important Terms
Terminologies used during Docker containerization are listed below:
Layer: Read-only files to provision the system
Image: Read-only layer that is the base of an image
Container: A runnable instance of the image
Registry/hub: A central place where images reside
Docker machine: A VM to run Docker containers
Docker Compose: A VM to run multiple containers as a system



Author: Sanni Michael(A senior software Engineer)
https://www.linkedin.com/in/sanni-michael-1385a1157/