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Docker Guide

Docker Compose

  • docker-compose up: Compose pulls a Redis image, builds an image for your code, and starts the services you defined.
  • docker-compose down: Stop the application (you can also do this by hitting CTRL+C in the original terminal where you started the app).
  • After modifying docker-compose.yml file, you need to rebuild the image by running docker-compose up again.
  • After modifying application, you can see the changes instantly without rebuilding the image.
  • If you want to run your services in the background, you can pass the -d flag (for "detached" mode) to docker-compose up.
  • docker-compose ps: Show what's currently running.

Docker

  • docker image ls: List all local docker images.
  • docker ps: List all docker containers.
  • docker inspect <tag or id>: Inspect a particular image based on the tag or id.
  • docker run -d nginx:1.10.0: Run the docker container in the background and print the container ID.
  • docker stop CONTAINERID: Stop the running containers with the container ID.
  • docker rm CONTAINERID: Remove the container and its used files.

Refer to https://docs.docker.com/get-started/ for quick start and https://docs.docker.com/engine/reference/commandline/docker/ for commands.

An Example of docker run

If you do $ docker run -i -t ubuntu /bin/bash, the following happens (assuming you are using the default registry configuration):

  • If you do not have the ubuntu image locally, Docker pulls it from your configured registry, as though you had run docker pull ubuntu manually.
  • Docker creates a new container, as though you had run a docker container create command manually.
  • Docker allocates a read-write filesystem to the container, as its final layer. This allows a running container to create or modify files and directories in its local filesystem.
  • Docker creates a network interface to connect the container to the default network, since you did not specify any networking options. This includes assigning an IP address to the container. By default, containers can connect to external networks using the host machine's network connection.
  • Docker starts the container and executes /bin/bash. Because the container is running interactively and attached to your terminal (due to the -i and -t flags), you can provide input using your keyboard while the output is logged to your terminal.
  • When you type exit to terminate the /bin/bash command, the container stops but is not removed. You can start it again or remove it.

Build and Deploy a Docker Image

To build a docker image, you need to prepare the source code and a Dockerfile (which specifies the instructions to build the application, the dependencies, as well as the command to run the program).

docker build -t haoranq4/image-name .

You can use the --platform flag to indicate which architecture you would like to build your image to run on, e.g., --platform linux/amd64,linux/arm64 .

You can check docker images to see whether your image is in the local docker repository. It should be there!

Then you can deploy your docker container by docker run -d -p 7001:7001 haoranq4/image-name.

  • -d means to run the container in background and print container ID.
  • -p 7001:7001 means to publish container's port 7001 (right) to the host machine's port 7001 (left).

You can delete the container by docker stop container-id and then docker rm container-id. The container id can be retrieved from docker ps.

You can push the image to the docker hub by docker image push haoranq4/image-name.

  • Login with your Docker Hub account required;

You can delete the image after all container instances are removed by docker image rm haoranq4/image-name.

Miscellaneous

Get the full container ID:

vagrant@dockertest:~$ docker ps
CONTAINER ID        IMAGE               COMMAND                CREATED              STATUS              PORTS               NAMES
ad6d5d32576a        nginx:latest        "nginx -g 'daemon of   About a minute ago   Up About a minute   80/tcp, 443/tcp     nostalgic_sammet
9bab1a42d6a9        nginx:latest        "nginx -g 'daemon of   About a minute ago   Up About a minute   80/tcp, 443/tcp     mad_kowalevski
beb70a6a2426        nginx:latest        "nginx -g 'daemon of   3 minutes ago        Up 3 minutes        80/tcp, 443/tcp     admiring_franklin

vagrant@dockertest:~$ docker ps -q --no-trunc | grep ad6d5d32576a
ad6d5d32576ad3cb1fcaa59b564b8f6f22b079631080ab1a3bbac9199953eb7d

Get the cgroup name with only the pid:

ps -o cgroup <pid>

SSH to a docker container:

sudo docker exec -it f5c4b82c9f2d /bin/bash

Docker Swarm

The following commands work for the Swarm orchestrator:

  • docker service ls: list all docker services
  • docker service ps: list tasks of one or more services
    • docker service ps redis
  • docker service create IMAGE: create a new service
    • docker service create --name redis redis:3.0.6
  • docker service inspect: display detailed information on one or more services
  • docker service logs: fetch the logs of a service
  • docker service rm: remove one or more services
    • docker service rm redis
  • docker service scale SERVICE=REPLICAS: scale one or more services
  • docker service update: update a service
    • docker service update --limit-cpu 2 redis
  • docker service rollback: roll back a service to its previous version
    • docker service create --name my-service -p 8080:80 nginx:alpine
    • docker service update --replicas=3 my-service (update the service to use three replicas)
    • docker service rollback myservice (roll back the service to its previous version with a single replica)

Install Docker on Mac (Doesn't work on M1 chip yet!)

brew install docker
brew install docker-machine
brew install virtualbox --cask
  • Why installing docker-machine?
    • This is because on macOS the docker binary is only a client and you cannot use it to run the docker daemon, because Docker daemon uses Linux-specific kernel features, therefore you can’t run Docker natively in OS X. So you have to install docker-machine in order to create VM and attach to it.
    • virtualbox is needed for creating VMs.

Then the next step is to create a new virtual machine. You can create a machine by docker-machine create (name) with --driver flag to specify a provider on which the machine is created on.

docker-machine create --driver virtualbox default
docker-machine ls

Run the following command to tell Docker which machine to execute docker command to:

docker-machine env default

Check the installation finally:

docker run hello-world

Create a Docker Image using Dockerfile

Example:

FROM python:3.8
ENV SRC_DIR /usr/bin/src/webapp/src
COPY web-server-senti.py ${SRC_DIR}/
COPY senti-data.json ${SRC_DIR}/
RUN pip install --no-cache-dir -U textblob
RUN python -m textblob.download_corpora
WORKDIR ${SRC_DIR}
ENV PYTHONUNBUFFERED=1
CMD ["python", "web-server-senti.py"]
  • In pip install, the flag --no-cache-dir allows one to save space in the final image.
  • ENV is used to set the environment variables also during the docker container runtime. Another alternative is ARG but this is used only during the container build time.

Copy a Docker Image

Copy a Docker image from a remote registry to a new image under different namespace/user, and then push to the new registry.

docker pull <image-name>
docker run -it <image-name> bash
docker ps
docker commit <container-id> <new-name>
docker push <new-name>

Rename the image:

docker image tag oldname:latest accountname/newname:latest

Copy files from Docker container to local

docker cp <containerId>:/file/path/within/container /host/path/target