webdev{docs}

Docker

Installation

You can follow the Docker installation instructions in the following Linux distributions:

Post installation

After installation, you have to make the user member of group docker :

sudo usermod -aG docker $USER

Commands

General

  • docker version: Checks docker version installed
  • docker info: Info about the docker environment
  • docker login -u "username": Access your Docker Hub repository

Images

  • docker images: List all available images in our host
  • docker pull nginx: Pull the nginx image from docker hub to our host
  • docker run -d nginx: Pull and start a new container based on nginx image (Pull only if image not present in local)
  • docker rmi nginx: Removes nginx image from our host

Containers

  • docker ps: List all running containers
  • docker ps -a: List all containers, running or not
  • docker stop 'container_name': Stops a running container
  • docker start 'container_name': Start a stopped container
  • docker rm 'container_name': Remove a non running container
  • docker rm 'container_name' -f: Remove a container, running or not
  • docker rm $(docker ps -aq): Remove all non running containers
  • docker rm $(docker ps -aq) -f: Remove all containers, running or not
  • docker exec -it 'container name' [BASH]: Access container file system command prompt. [BASH] can be /bin/bash or /bin/sh
  • docker create nginx top: Create a writeable container layer over the specified image and prepares it for running the specified command.
  • docker logs 'container_name': Fetch the logs of the container.

Creating a nginx container

docker run -d -p 8080:80 --name mynginx nginx

To browse, visit localhost:8080 on a web browser

To access the container's shell, issue:

docker exec -it mynginx bash or sh

Pages are served from /usr/share/nginx/html

Volumes

Volumes for development use

  • Dockerfile:
FROM php:7.2-apache
COPY src/ /var/www/html/
EXPOSE 80

home/user/mywebsite:~$: docker build -t myimage .

The above command does the following:

  • Build an image of an apache server with php
  • Copy the content of /home/user/mywebsite/src/ into the the apache /var/www/html/ serving directory
  • Expose port 80 so it can be reached

Next we run:

docker run -d -p 8080:80 -v /home/user/mywebsite/src/:/var/www/html --name mywebsite myimage

The above command does the following:

  • Create a nginx container in the background called mywebsite
  • Use port 8080 to access the website
  • Mount the container directory /var/www/html/ on to local directory /home/user/mywebsite/src/ where the source code of the site is held.
  • We can now create and edit index.php and other files and directories directly in /home/user/mywebsite/src/, and it will update automatically.
  • We can visit the website on localhost:8080

Delete unused or lost volumes

$ docker volume rm $(docker volume ls -qf dangling=true)
$ docker volume ls -qf dangling=true | xargs -r docker volume rm

Building our own image

Providing we have these files in the directory where we are going to issue the build command:

  • about.html
  • contact.html
  • index.html
  • services.html

We create and edit the following file: Dockerfile 

FROM nginx:latest
WORKDIR /usr/share/nginx/html
COPY . .

And now we issue the build command:

docker image build -t nginx-mywebsite .

Pushing our new created image to Docker Hub

docker tag nginx-mywebsite nginx-mywebsite:v1
docker tag nginx-mywebsite <dockerhubusername>/<nginx-mywebsite>|<fooimage>
docker login
docker push <dockerhubusername>/nginx-mywebsite
docker logout

Note: It takes 24-48 hours for Docker Hub to index the image

Docker compose

docker-compose up -d
docker-compose down
docker-compose down --volumes

Scaling

Scaling services with docker-compose is as simple as:

docker-compose up -d --scale myservice=3

Swarm

  • Start a Swarm cluster master node
docker swarm init --advertise-addr [IP_ADDRESS]

Copy the token

  • Add a node in the Swarm cluster

From a new machine, issue:

docker swarm join --token [the_copied_token] [IP_ADDRESS_OF_MASTER_NODE]:2377
  • See all nodes in the cluster
docker node ls
  • Create/Deploy a service/application in the Swarm cluster
docker service create --name [NAME] --publish published=8080,target=80 --replicas 2 httpd
  • See running servcies
docker sevice ls
  • See specific service information
docker service ps [NAME]
  • Scale a servcie
docker service scale [NAME]=3
  • Update a service with a new/old version
docker service update --image redis:3.0.7 redis
  • Delete Swarm machine
rm -rf /var/lib/docker/swarm
systemctl restart docker

Tips and Hints

  • If there's a need to run Docker containers in production without Kubernetes, use the --init flag upon docker run . This injects a PID 1 process, which handles its terminated children correctly, into the container to run.

  • There are four important files that acts as contracts between deverlopers and sys admins:

    • Dockerfile: To build or application image
    • docker-compose.yml: To execute our application
    • Dockerfile.test: To build our application test image
    • docker-test.yml: Test our application