DockerNotes

Repository for Docker learning notes, resources, and code

Installation

Follow the steps in https://docs.docker.com/engine/install/

Check installation: sudo docker version

Basic Commands

Run: start a container (1) with a local image (2) pull an image from Docker Hub

• A Docker container stops when the app inside finishes execution
• Append a command: docker run ubuntu sleep 5

ps: lists the running container information

stop: stops a running container (with ID or Name)

rm: permanently removes a container

image: image commands such as list images, sizes, etc

rmi: removes images (be sure to remove all depedent containers before removing an image)

pull: downloads an image from a repository

exec: execute a command on a running container

detach & attach: running docker container in background/foreground

• docker run -d [DOCKER-APP]
• docker attach [CONTAINER-ID]

Docker Run

docker run [OPTIONS] IMAGE [COMMAND] [ARG...]

Example: docker run redis:4.0

• Port mapping: -p [EXT PORT][INT PORT]

• Volume mapping: -v [EXT PATH]:[INT PATH]

  Store data inside a container in host. The data will be preserved even after the container is destroyed.

  Example: docker run -v /opt/datadir:/var/lib/mysql mysql

• More container detail in JSON format: docker inspect [CONTAINER ID/NAME]

• Container logs: docker log [CONTAINER ID/NAME]:

• Setting Environment variables: -e VAR_NAME=VALUE

Creating Own Images with Dockerfiles

1. Write a docker file executing all the steps for setting up the dev environment
2. Build the docker image: docker build -t [NAME:TAG] [CONTEXT PATH]
3. Push the image to the Docker Hub: docker push [IMAGE NAME]

Specifying the program to execute and parameters for Dockerfile

Both ENTRYPOINT and CMD give you a way to identify which executable should be run when a container is started from your image

CMD:

• has two formats (1) CMD COMMAND PARAM1 PARAM2 ... (2) CMD ["COMMAND", "PARAM", ...]
• The command and parameters can be overridden with docker run

ENTRYPOINT:

• parameters can be appended with docker run

Combining CMD and ENTRYPOINT

FROM Ubuntu
ENTRYPOINT ["sleep"]
CMD ["5"] # default parameter that can be overridden

Docker Networks

Three default networks: bridge, none, host

Example: docker run --network=wp-mysql-network -e DB_Host=mysql-db -e DB_Password=db_pass123 -p 38080:8080 --name webapp --link mysql-db:mysql-db -d kodekloud/simple-webapp-mysql

Docker Compose

Configuration of running multiple containers with YAML files

Setting up

1. Specify the container names and images in the .yml file
2. Run docker-compose up

Container Orchestration: Docker Swarm

• Used for automatic load balancing and avoiding host failure on multiple servers.
• Popular container orchestration services: Docker Swarm, Kubernetes, MESOS
• Example: docker service create --replicas=100 nodejs