Learn Docker via PostHog

The goal of this project is to (1) have a tiny docker environment for localdev that works on Apple M1 and (2) learn Docker in the process. You can read the progress of this repo in the project doc.

Docker Nomenclature and Notes

• Docker Image - the actual package, artifact which can be shared with others, docker images are built in layers via Dockerfile
• Docker Container - a running instance of a docker image, file system is virtual, contains a port for communication
• Docker run - command which executes pull and start (only pulls images we do not have locally)
• Docker vs Virtual Machine
  • Operating System = Hardware > OS Kernel (layer 1) > Applications (layer 2)
  • Docker = Virtualization of applications (layer 2)
  • Virtual Image = Virtualization of OS (layer 1)
  • Benefits of Docker = images are much smaller, runs faster
  • Benefits of VM = you can run different OS (Windows on Linux) since it has it's own OS Kernel
• Docker Port vs Host Port
  • Multiple containers may use the same port
  • Bind host port to docker port, i.e. host 3000 -> docker 3000, host 3001 -> docker 3000
• Docker Compose
  • Configuration file specifying docker commands to make it easier to work with
  • Automatically handles creating a common docker network
  • Docker compose is usually installed with docker so you already have it
• Docker Volumes
  • Provides data persistence between host machine and docker containers
  • The data between volumes is replicated between the host and docker container volumes
  • 3 docker volume types: specified, anonymous, and named volumes, named volumes on the host are managed by docker
  • Production should use named volumes
  • Container Mongodb = /data/db
  • Container MySQL = /var/lib/myself
  • Container Postgres = /var/lib/postgres/data
  • Host Windows = C:\ProgramData\docker\volumes
  • Host Linux = /var/lib/docker/volumes/[hash]/_data
  • Host Mac = /var/lib/docker/volumes/[hash]/_data
    • screen ~/Library/Containers/com.docker.docker/Data/com.docker.driver.amd64-linux/tty add access linux VM on mac where data is stored, ctrl + a + k to exit screen session

Basic commands

• docker pull downloads a docker image locally
• docker images shows a list of local docker images and their sizes
• docker run run a docker container, it's two commands in one docker pull and docker start
• docker run -d runs the docker container in detach mode
• docker run -p binds the container to host port i.e. -p6000:6370, -p [host]:[container]
• docker run --name give the container a name so that you do not need to use the SHA
• docker run -d -it python runs python images in interactive terminal mode
• docker run -e runs an image with an environment variable
• docker run -net specify a docker network to run within
• docker start start a container, retains the settings from the run command
• docker stop - stops a container
• docker ps shows running containers
• docker ps -a shows running and not-running containers
• docker logs shows the standard output of the running container
• docker logs -f follow the standard output, similar to tail -f
• docker exec -it runs the container with interactive terminal
• docker network ls shows a list of the internal docker network
• docker network create create a docker network
• docker build -t my-app:1.0 . builds an image from a Dockerfile in the current directory
• docker rm removes a docker container which you need to do before docker rmi
• docker rmi removes a docker image, i.e. docker rmi my-app:1.0
• docker run -v mounts host filesystem to docker container filesystem
• docker system prune clean up any images, containers, volumes, and networks that are dangling
• docker system prune -a any stopped containers and all unused images

Docker Compose

• docker-compose -f mongo.yaml up pulls, starts, and creates container network
• docker-compose -f mongo.yaml up -d runs containers in detached mode
• docker-compose -f mongo.yaml down stops container, removes container, and stops container network

First Dockerfile

FROM python:3.9-alpine3.13

RUN apk add bash nodejs

COPY hello.* /

CMD ["bash"]

First commands

• docker build . builds the container
• docker run --name [name] [sha] installs the container
• docker run -it --name [name] [sha] installs the container and starts in interactive mode
• docker ps shows all the running containers
• docker ps -a shows all the running and exited containers
• docker stop [name] stop container
• docker start -ai [name] start container interactively
• docker rm [name] removes container

Getting started

• git clone https://github.com/buwilliams/tiny-posthog.git
• cd tiny-posthog
• docker build .
• docker run -it --name test [sha] find sha in the output from docker build

Resources

• Creating your first Dockerfile, image and container great place to start
• Docker Tutorial for Beginners [FULL COURSE in 3 Hours] most helpful
• Docker For Beginners: From Docker Desktop to Deployment

Related Resources

• Kubernetes Tutorial for Beginners FULL COURSE in 4 Hours To manage distribution of contains across many servers

Ideas

• It's possible to run only the containers that are needed for PostHog's EE
• Build Clickhouse for ARM64
• Is it possible to docker-compose conditionally based on architecture? If so, I think we have a solution for PostHog EE on Macbook Silicon/M1.
  • This Stack Overflow question may contain the answer. Solution: generate docker compose files