Docker/Container Introduction

What is Docker?

Docker is an open platform for developing, shipping, and running applications. Docker enables you to separate your applications from your infrastructure so you can deliver software quickly. With Docker, you can manage your infrastructure in the same ways you manage your applications. By taking advantage of Docker’s methodologies for shipping, testing, and deploying code quickly, you can significantly reduce the delay between writing code and running it in production.

https://www.docker.com/company/newsroom/media-resources

Pattern: Service instance per container

Context

You have applied the Microservice architecture pattern and architected your system as a set of services. Each service is deployed as a set of service instances for throughput and availability.

Problem

How are services packaged and deployed?

Solution

Package the service as a (Docker) container image and deploy each service instance as a container

Installing Docker

Get Docker

First Steps

Now that you have Docker installed, lets have a quick look at what’s available.

let’s view the version numbers for the Docker installation. This is also a great way to ensure Docker is installed and running correctly.

docker version

Output similar to this

Client:
 Cloud integration: v1.0.22
 Version:           20.10.11
 API version:       1.41
 Go version:        go1.16.10
 Git commit:        dea9396
 Built:             Thu Nov 18 00:42:51 2021
 OS/Arch:           windows/amd64
 Context:           default
 Experimental:      true
Server: Docker Engine - Community
 Engine:
  Version:          20.10.11
  API version:      1.41 (minimum version 1.12)
  Go version:       go1.16.9
  Git commit:       847da18
  Built:            Thu Nov 18 00:35:39 2021
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.4.12
  GitCommit:        7b11cfaabd73bb80907dd23182b9347b4245eb5d
 runc:
  Version:          1.0.2
  GitCommit:        v1.0.2-0-g52b36a2
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

Docker architecture (Reference : https://docs.docker.com/get-started/overview/)

Docker uses a client-server architecture. The Docker client talks to the Docker daemon, which does the heavy lifting of building, running, and distributing your Docker containers. The Docker client and daemon can run on the same system, or you can connect a Docker client to a remote Docker daemon. The Docker client and daemon communicate using a REST API, over UNIX sockets or a network interface. Another Docker client is Docker Compose, that lets you work with applications consisting of a set of containers.

Reference : https://docs.docker.com/get-started/overview/

Docker daemon

The Docker daemon (dockerd) listens for Docker API requests and manages Docker objects such as images, containers, networks, and volumes. A daemon can also communicate with other daemons to manage Docker services.

Docker client

The Docker client (docker) is the primary way that many Docker users interact with Docker. When you use commands such as docker run the client sends these commands to dockerd, which carries them out. The docker command uses the Docker API. The Docker client can communicate with more than one daemon.

Docker registries

A Docker registry stores Docker images. Docker Hub is a public registry that anyone can use, and Docker is configured to look for images on Docker Hub by default. You can even run your own private registry.

When you use the docker pull or docker run commands, the required images are pulled from your configured registry. When you use the docker push command, your image is pushed to your configured registry.

Docker objects

When you use Docker, you are creating and using images, containers, networks, volumes, plugins, and other objects. This section is a brief overview of some of those objects.

Images

An image is a read-only template with instructions for creating a Docker container. Often, an image is based on another image, with some additional customization. For example, you may build an image which is based on the ubuntu image, but installs the Apache web server and your application, as well as the configuration details needed to make your application run.

Containers

A container is a runnable instance of an image. You can create, start, stop, move, or delete a container using the Docker API or CLI. You can connect a container to one or more networks, attach storage to it, or even create a new image based on its current state.

Top Docker Commands

docker version
docker pull 
docker run
docker ps
docker ps -a
docker exec
docker stop
docker kill
docker commit
docker login
docker push
docker images
docker rm
docker rmi
docker build
docker info

docker pull

Pull an image or a repository from a registry

docker run

Run a command in a new container

docker run -it -d ubuntu

Output similar to this

4e4d49a5495585d80a6e8e9ddd9e5ab3336a1247c93f068fa353fbb95a75e6d6

docker ps

List containers

docker ps

Output similar to this

CONTAINER ID   IMAGE     COMMAND                  CREATED          STATUS          PORTS                               NAMES
4e4d49a54955   ubuntu    "bash"                   47 seconds ago   Up 46 seconds                                       elegant_moser

docker ps -a

Show all containers (default shows just running)

docker ps -a

Output similar to this

CONTAINER ID   IMAGE     COMMAND                  CREATED              STATUS                     PORTS     NAMES
4e4d49a54955   ubuntu    "bash"                   About a minute ago   Up About a minute                    elegant_moser
3d75c8252715   mysql     "docker-entrypoint.s…"   4 weeks ago          Exited (0) 8 seconds ago             setup-mysql_db_1

docker exec

Run a command in a running container

docker exec -it 4e4d49a54955 bash
root@4e4d49a54955:/# echo "hi" > /home/demo.txt
root@4e4d49a54955:/# cat /home/demo.txt
hi

docker commit

Create a new image from a container’s changes

docker commit 4e4d49a54955 app:1.0

Output similar to this

sha256:aa62d74330275add9450*************************************

docker stop

Stop one or more running containers

docker stop 4e4d49a54955

Output similar to this

4e4d49a54955

docker start

docker start 4e4d49a54955

Output similar to this

4e4d49a54955

docker kill

Kill one or more running containers

docker kill 4e4d49a54955

Output similar to this

4e4d49a54955

docker login

Log in to a Docker registry or cloud backend. If no registry server is specified, the default is defined by the daemon.

docker login

Output similar to this

Login with your Docker ID to push and pull images from Docker Hub. If you don't have a Docker ID, head over to <https://hub.docker.com> to create one.
Username ([username]):
Password: **********

docker push

Push an image or a repository to a registry

docker push app:1.0

docker images

List images

docker images

Output similar to this

REPOSITORY                                           TAG                                                     IMAGE ID       CREATED          SIZE
app                                                  1.0                                                     aa62d7433027   11 minutes ago   72.8MB
ubuntu                                               latest                                                  54c9d81cbb44   14 minutes ago    72.8MB

docker rm

Remove one or more containers

docker rm ccd3f585bb2a

Output similar to this

ccd3f585bb2a

docker rmi

Remove one or more images

docker rmi app:1.0

Output similar to this

Untagged: app:1.0
Deleted: sha256:aa62d74330275add945070457b21c9da20d712f2717f3f803cd8e434f2b65d32
Deleted: sha256:878d2ffe799cf21525e9b4ae727df1e0f5c3c0122c7d5fdc8843e8a92f6ff87c

docker build

Build an image from a Dockerfile

A Dockerfile looks like this:

FROM ubuntu:latest
RUN apt-get update
RUN apt-get install -y nginx
ENTRYPOINT ["/usr/sbin/nginx","-g","daemon off;"]
EXPOSE 80
docker build -t custom-ngnix:1.0 .

Output similar to this

[+] Building 0.1s (7/7) FINISHED
 => [internal] load build definition from Dockerfile                                                            0.0s
 => => transferring dockerfile: 169B                                                                            0.0s
 => [internal] load .dockerignore                                                                               0.0s
 => => transferring context: 2B                                                                                 0.0s
 => [internal] load metadata for docker.io/library/ubuntu:latest                                                0.0s
 => [1/3] FROM docker.io/library/ubuntu:latest                                                                  0.0s
 => CACHED [2/3] RUN apt-get update                                                                             0.0s
 => CACHED [3/3] RUN apt-get install -y nginx                                                                   0.0s
 => exporting to image                                                                                          0.0s
 => => exporting layers                                                                                         0.0s
 => => writing image sha256:f9b17c40d4a92460a6a1918c2503d2c0e12c3b515e542d1c709d6dad022e9365                    0.0s
 => => naming to docker.io/library/custom-ngnix:1.0                                                             0.0s

docker info

Display system-wide information

Client:
 Context:    default
 Debug Mode: false
 Plugins:
  buildx: Docker Buildx (Docker Inc., v0.7.1)
  compose: Docker Compose (Docker Inc., v2.2.1)
  scan: Docker Scan (Docker Inc., v0.14.0)
Server:
 Containers: 35
  Running: 33
  Paused: 0
  Stopped: 2
 Images: 38
 Server Version: 20.10.11
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Native Overlay Diff: true
  userxattr: false
 Logging Driver: json-file
 Cgroup Driver: cgroupfs
 Cgroup Version: 2
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
 Swarm: inactive
 Runtimes: runc io.containerd.runc.v2 io.containerd.runtime.v1.linux
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: 7b11cfaabd73bb80907dd23182b9347b4245eb5d
 runc version: v1.0.2-0-g52b36a2
 init version: de40ad0
 Security Options:
  seccomp
   Profile: default
  cgroupns
 Kernel Version: 5.10.76-linuxkit
 Operating System: Docker Desktop
 OSType: linux
 Architecture: x86_64
 CPUs: 6
 Total Memory: 1.909GiB
 Name: docker-desktop
 ID: JHIS:7TJM:OPIA:JYFM:2XCV:KUM3:Y4BY:YDJC:6VDD:L4GA:DM74:PAOD
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 Registry: <https://index.docker.io/v1/>
 Labels:
 Experimental: false
 Insecure Registries:
  127.0.0.0/8
 Live Restore Enabled: false

Docker Compose

Compose is a tool for defining and running multi-container Docker applications. With Compose, you use a YAML file to configure your application’s services. Then, with a single command, you create and start all the services from your configuration.

A docker-compose.yml looks like this:

version: '3.1'
services:
  web:
    image: open-liberty:21.0.0.9-full-java8-openj9
    restart: always
    ports:
      - "9199:9080"

to run compose file

docker compose up

Useful links

Overview of Docker Compose

Docker Documentation

Open Container Initiative

Alternatives to Docker

The Open Container Initiative (OCI) is an industry standards organization that encourages innovation while avoiding the danger of vendor lock-in. Thanks to the OCI, you have a choice when choosing a container toolchain, including Docker, CRI-O, Podman, LXC, and others.

The OCI currently contains two specifications: the Runtime Specification (runtime-spec) and the Image Specification (image-spec). The Runtime Specification outlines how to run a “filesystem bundle” that is unpacked on disk. At a high-level an OCI implementation would download an OCI Image then unpack that image into an OCI Runtime filesystem bundle. At this point the OCI Runtime Bundle would be run by an OCI Runtime.

https://opencontainers.org/