/Docker123

Experimenting with Docker

MIT LicenseMIT

Docker123

Experimenting with Docker

Resources used

Topics left

  • Docker Machine
  • Docker Swarm
  • Docker Compose

Install and verify if docker is installed properly

wget -qO https://get.docker.com/ | sh
sudo docker run hello-world
sudo usermod -aG docker <user>

docker version
docker images

Sudo docker run [options] [image] [command] [args]
Docker run -i(tells docker to connect to STDIN on the container) -t(specifies to get a pseudo-terminal) ubuntu:latest /bin/bash

Exit the container without actually stopping the container -> Ctrl + P + Q

A docker has two IDs:

  • Short ID
  • Long ID

Display all the running and stopped dockers:

docker ps -a

Running docker in detached mode (or as a daemon or background process):

docker run -d centos:7 ping 127.0.0.1 -c 100

Display the logs of a running or stopped container:

Docker logs [shortID]

Create a container using the tomcat image, run in detached mode and map the tomcat ports to the host port

docker run -d -P tomcat:7

Building Images

  1. Image Layers
  2. The container writable layer

Docker Commit

  • saves changes in a container as a new image
  • docker commit [options] [container ID] [repository:tag]
  • repository name should be based on username/application
  • can reference the container with container name instead of ID
  • ex:docker commit [ID] panda/myapplication:1.0
docker run -it ubuntu:latest /bin/bash

apt-get -qq update
apt-get install curl
docker ps -a
docker commit <container ID> <yourname>/curl:1.0
docker images
docker run -it <yourname>/curl:1.0 bash

Dockerfile

  • is a configuration file that contains instructions for building a Docker image
  • FROM instruction specifies what the base image should be
  • RUN instruction specifies a command to execute
  • EX:
FROM ubuntu:latest
RUN apt-get install vim
RUN apt-get install curl
  • each RUN instruction will execute the command on the top writable layer and perform a commit of the image

Docker Build

  • docker build [options] [path]
  • docker build -t [repository:tag] [path]
  • EX: docker build -t pisceanpanda/myimage:1.0 .

CMD Instruction

  • defines a default command to execute when a container is created
  • performs no action during image build
  • can only be specified once in a docker file
  • EX: CMD ["ping", "127.0.0.1", "-c","10"]
  • container argument overrides the CMD instruction

ENTRYPOINT

MANAGING IMAGES AND CONTAINERS

docker ps -a
docker start <container ID>
docker stop <container ID>
docker rm <container ID>

docker images
docker rmi [image ID]
docker rmi [repo:tag]

Publishing Images

docker login
docker tag [local repo:tag] [Docker Hub repo:tag]
docker push [repo:tag]

VOLUME

  • is a designated directory in a container, which is designed to persist data, independent of the container's life cycle
  • volume changes are excluded when updating an image
  • persist when a container is deleted
  • can be mapped to a host folder
  • can be shared between containers

Mount Volumes

  • can be mounted when creating or executing a container
  • can be mapped to a host directory
  • volume paths specified must be absolute
  • Execute a new container and mount the folder /myvol into its FS docker run -d -P -v /myvol nginx:1.7
  • Execute a new container and map the /data/src folder from the host into the /test/src folder in the container docker run -i -t -v /data/src:/test/src nginx:1.7

Volumes in Dockerfile

  • VOLUME instruction creates a mount point
  • can specify arguments in JSON array or string
  • cannot map volumes to host directories
  • volumes are initialized when the container is executed
  • String example VOLUME /myvol
  • JSON example VOLUME ["myvol1", "myvol2"]

Uses of volume

  • decouple the data that is stored from the container which created the data
  • good for sharing data b/w containers can setup a data container which has a volume you mount in other containers
  • mounting folders from the host is good for testing purposes but generally not recommended for production use

Container Networking Features

Mapping Ports:

  • containers have their own n/w and IP address
  • map exposed container ports to ports on the host machine
  • ports can be manually mapped or auto mapped
  • uses -p and -P parameters in the docker run
  • EX: docker run -d -P 8080:80 nginx:1.7 -P option automatically maps exposed ports in the container to a port number in the host
  • only works for ports defined in the EXPOSE instruction

Linking Containers

  • linking is a communication method between containers which allows the mt o securely transfer data from one to another.
  • recipient containers have access to data on source containers
  • links are established based on container names

Creating a Link

  • create the source container first docker run -d --name databasedocker postgres
  • create the recipient container and use the --link option docker run -d -P --name website --link databasedocker:db nginx

Uses of Linking

  • containers can talk to each other without having to expose ports to the host
  • essential for micro service application architecture
  • Example:
  1. container with tomcat running
  2. container with MySQL running
  3. application on tomcat needs to connect to MySQL

Docker in Continuous Integration

  • CI server builds docker image and pushes into docker hub
  • docker hub auto build
  1. detects commits to source repository and builds the image
  2. container is run during image build
  3. testing done inside container