Docker in Action

Let’s learn docker by handson

Let’s get to know docker more by executing cli commands

Docker Commands

Command	Description	Example
docker info	Display system-wide information	docker info
docker version	Show the Docker version information	docker version
docker pull	Pull an image or a repository from a registry	docker pull redis
docker images	List images	docker images
docker run	Run a command in a new container	docker run -d redis

Command	Description	Example
docker ps	List containers	docker ps
docker exec	Run a command in a running container	docker exec -it <id/name> sh
docker inspect	Return low-level information on Docker objects	docker inspect <object id/name>
docker logs	Fetch the logs of a container	docker logs <id/name>

Command	Description	Example
docker stats	Display a live stream of container(s) resource usage statistics	docker stats
docker network	Manage networks	docker network ls
docker rename	Rename a container	docker rename <old> <new name>

Command	Description	Example
docker stop	Stop one or more running containers	docker stop <id/name>
docker rm	Remove one or more containers	docker rm <id/name>
docker rmi	Remove one or more images	docker rmi <image id>

Command	Description	Example
docker volume	Manage volumes	docker volume ls
docker build	Build an image from a Dockerfile	dockr build . -t myapp:v1

Command Help

docker [command] --help

Example

> docker exec --help

Usage:	docker exec [OPTIONS] CONTAINER COMMAND [ARG...]

Run a command in a running container

Options:
  -d, --detach               Detached mode: run command in the background
      --detach-keys string   Override the key sequence for detaching a container
  -e, --env list             Set environment variables
  -i, --interactive          Keep STDIN open even if not attached
      --privileged           Give extended privileges to the command
  -t, --tty                  Allocate a pseudo-TTY
  -u, --user string          Username or UID (format: <name|uid>[:<group|gid>])
  -w, --workdir string       Working directory inside the container

More commands

https://docs.docker.com/engine/reference/commandline/docker/

Docker Volumes Usecase

Jenkins

Jenkins version updates
Plugin updates
Without losing configs/jobs you already have

Docker run with volumes

docker run -p 8080:8080 -p 50000:50000 -v jenkins_home:/var/jenkins_home jenkins/jenkins:lts

This will store the workspace in /var/jenkins_home
All Jenkins data lives in there - including plugins and configuration
This will automatically create a ‘jenkins_home’ docker volume on the host machine, that will survive the container stop/restart/deletion

View docker volume created

docker volume ls

Alpine Images

Alpine Linux is a security-oriented, lightweight Linux distribution based on musl libc and busybox
Alpine image is only 5MB and has access to a package repository
https://github.com/alpinelinux/docker-alpine

Why Alpine Images?

Docker images today are big
Usually much larger than they need to be
There are a lot of ways to make them smaller, but the Docker populace still jumps to the ubuntu base image for most projects
The size savings over ubuntu and other bases are huge:

REPOSITORY  TAG     IMAGE ID      CREATED      SIZE
alpine      latest  961769676411  4 weeks ago  5.58MB
ubuntu      latest  2ca708c1c9cc  2 days ago   64.2MB
debian      latest  c2c03a296d23  9 days ago   114MB
centos      latest  67fa590cfc1c  4 weeks ago  202MB

Alpine based images vs normal

ruby  2.6.6            39853018958e      13 days ago    840MB
ruby  2.6.6-alpine     d86341b50737      5 weeks ago    49.8MB

Building Images

Dockerfile

Docker can build images automatically by reading the instructions from a Dockerfile
A Dockerfile is a text document that contains all the commands a user could call on the command line to assemble an image
Using docker build users can create an automated build that executes several command-line instructions in succession

Example

FROM ubuntu

RUN apt-get update
RUN apt-get install –y nginx
CMD [“echo”,”Image created”]

Dockerfile Commands

Command	Description
FROM	specify base image
RUN	execute commands
ENTRYPOINT	to configure a container that will run as an executable
CMD	provide defaults for an executing container
COPY	copies new files or directories

Command	Description
ENV	sets the environment variable
EXPOSE	informs Docker that the container listens on the specified network ports
USER	sets the user
WORKDIR	sets the working directory

Lets build images

From terminal/git bash

git clone https://github.com/slashpai/docker_k8s_training.git
cd docker_k8s_training
cd docker_apps

Example 1

Simple WebApp

cd simple_webapp

A simple ruby web app using Sinatra
Lets understand the app first
Lets build the docker app from it
docker build . -t simple-webapp:v1

Run docker containers

docker run -d -p 9000:4567 –name simple-webapp1 simple-webapp:v1
docker run -d -p 9001:4567 –name simple-webapp1 –env APP_COLOR=yellow simple-webapp:v1
docker run -d -p 9002:4567 –name simple-webapp2 –env APP_COLOR=orange simple-webapp:v1
Go to http://localhost:9000, http://localhost:9001 and http://localhost:9002

Understanding Dockerfile

FROM ruby:2.6.6-alpine

WORKDIR /usr/src/app

ENV APP_COLOR="pink"

COPY Gemfile ./

RUN gem install bundler && bundle install

COPY . .

EXPOSE 4567

CMD [ "ruby", "app.rb" ]

Example 2

Ruby Calculator

cd calculator

A simple ruby calaculator to show how we can use docker to run adhoc tasks
Lets understand the app first
Lets build the docker app from it
docker build . -t simple-calculator:v1
docker run simple-calculator:v1 3 + 4

Review the container created

docker ps
docker ps -a
Any reason why it doesn’t show in running container list?
Noticed the ENTRYPOINT in Dockerfile?

Understanding Dockerfile

FROM ruby:2.6.6-alpine

WORKDIR /usr/src/app

COPY . .

ENTRYPOINT ["ruby", "calculator.rb"]

.dockerignore file

Before the docker CLI sends the context to the docker daemon, it looks for a file named .dockerignore in the root directory of the context
If this file exists, the CLI modifies the context to exclude files and directories that match patterns in it
This helps to avoid unnecessarily sending large or sensitive files and directories to the daemon and potentially adding them to images using ADD or COPY

Example 3

Quiz App

cd quiz_app

A simple quiz app using node.js
Noticed the .dockerignore file?
Lets build the docker app from it
docker build . -t quiz-app:v1

Some task for you

docker run -d -p 3500:3000 quiz-app:v1
Go to http://localhost:3500
Try the docker quiz 🤩

Understanding Dockerfile

FROM node:15.3.0-alpine3.10

# Create app directory
WORKDIR /usr/src/app

# Install app dependencies
COPY package*.json ./

RUN npm install

# Bundle app source
COPY . .

EXPOSE 3000
CMD [ "node", "index.js" ]

CMD vs ENTRYPOINT

CMD is an instruction that is best to use if you need a default command which users can easily override
ENTRYPOINT is preferred when you want to define a container with a specific executable
You cannot override an ENTRYPOINT when starting a container unless you add the –entrypoint flag
Combine ENTRYPOINT with CMD if you need a container with a specified executable and a default parameter that can be modified easily

Explore Dockerfiles of some of the official images available in docker hub

https://hub.docker.com/search?q=&type=image&image_filter=store%2Cofficial

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

Commands

docker-compose <command>

  build              Build or rebuild services
  config             Validate and view the Compose file
  create             Create services
  down               Stop and remove containers, networks, images, and volumes
  exec               Execute a command in a running container
  help               Get help on a command
  images             List images
  logs               View output from containers
  ps                 List containers
  restart            Restart services
  rm                 Remove stopped containers
  start              Start services
  stop               Stop services
  up                 Create and start containers
  version            Show the Docker-Compose version information

Example Application

https://github.com/slashpai/voter-app

version: "3.7"

services:
  vote:
    build: .
    command: /voter-app
    environment:
      VOTER_REDIS_ADDR: "voter-app_redis_1:6379"
      VOTER_REDIS_PASSWORD: ""
      VOTER_REDIS_DB: 0
    ports:
      - "8090:8080"
  redis:
    image: redis:alpine
    ports: ["6379"]
    volumes:
      - voter_redis_data:/data
volumes:
  voter_redis_data: {}

Other Examples

version: "3.7"

services:
  prometheus:
    image: prom/prometheus:v2.19.0
    container_name: prom
    ports:
      - "9090:9090"
  grafana:
    image: grafana/grafana:7.0.3
    container_name: grafana
    ports:
      - "3000:3000"

Let’s try docker-compose

cd to docker_k8s_training/docker-compose/monitoring
docker-compose up

Load http://localhost:3000 and http://localhost:9090

cd to docker_k8s_training/docker-compose/consul_cluster
docker-compose up

Load http://localhost:8500

Run in detached mode/background

docker-compose up -d

Explore docker-compose commands

docker-compose ps
docker-compose images
docker-compose stop
docker-compose rm

https://docs.docker.com/compose/gettingstarted/

Docker Image Layers Review

Compare images docker history image:tag

https://docs.docker.com/storage/storagedriver/

Clean Up Unused containers/images

docker stop
docker rm

docker images
docker rmi

List all exited containers

docker ps -a -f status=exited

Remove all exited containers

docker rm $(docker ps -a -f status=exited -q)

Docker Images Cleanup

Docker images consist of multiple layers. Dangling images are layers that have no relationship to any tagged images
They no longer serve a purpose and consume disk space
If you build an image without tagging it, the image will appear on the list of dangling images
```
docker images -f dangling=true
```
When you’re sure you want to delete them
```
docker image prune
```

To remove specific image
- You would require to first stop and remove container using the image before doing this
```
docker rmi <image id/name:tag>
```

https://www.digitalocean.com/community/tutorials/how-to-remove-docker-images-containers-and-volumes

Training Summary

Docker commands
Building docker applications and run it
Using Docker compose

What Next?

Want to learn something new without the pain of installing and messing up your machine?
You know the answer how to solve that now 🤩

Docker in Action

Let’s get to know docker more by executing cli commands

Docker Commands

Command Help

Example

More commands

Docker Volumes Usecase

Docker run with volumes

View docker volume created

Alpine Images

Why Alpine Images?

Alpine based images vs normal

Building Images

Dockerfile

Example

Dockerfile Commands

Lets build images

From terminal/git bash

Example 1

Simple WebApp

Run docker containers

Understanding Dockerfile

Example 2

Ruby Calculator

Review the container created

Understanding Dockerfile

.dockerignore file

Example 3

Quiz App

Some task for you

Understanding Dockerfile

CMD vs ENTRYPOINT

Explore Dockerfiles of some of the official images available in docker hub

Docker Compose

Commands

Example Application

Other Examples

Let’s try docker-compose

Run in detached mode/background

Explore docker-compose commands

Read More

Docker Image Layers Review

Read More

Clean Up Unused containers/images

List all exited containers

Remove all exited containers

Docker Images Cleanup

Read More

Training Summary

What Next?

Thank you!

Any questions?