A quick reference to Docker.
Created on: 2019-03-19
Tag: cheat_sheet
Warning
under heavy construction and not well organized
to docker install on ubuntu:
sudo apt-get remove docker docker-engine docker.io -y sudo apt-get update sudo apt-get install apt-transport-https ca-certificates curl software-properties-common -y curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add - sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable" sudo apt-get update sudo apt-get install docker-ce -y
source: https://docs.docker.com/v17.09/engine/installation/linux/docker-ce/ubuntu/
Warning
This is not recommanded as it creates an attack serface for privilege escalation. See more at: Privilege escalation via Docker<https://fosterelli.co/privilege-escalation-via-docker>. To fix this just remove the user from docker group with sudo gpasswd -d $USER docker.
after install:
sudo groupadd docker sudo usermod -aG docker $USER
Now logout or reboot to see the change in effect.
source: https://docs.docker.com/v17.09/engine/installation/linux/linux-postinstall
test your installation:
sudo docker run hello-world
to install docker-compose on ubuntu:
sudo curl -L "https://github.com/docker/compose/releases/download/1.24.1/docker-compose-$(uname -s)-$(uname -m)" -o /usr/local/bin/docker-compose sudo chmod +x /usr/local/bin/docker-compose
to have bash compilation for docker-compose:
sudo curl -L https://raw.githubusercontent.com/docker/compose/1.24.1/contrib/completion/bash/docker-compose -o /etc/bash_completion.d/docker-compose
now restart bash
https://stackoverflow.com/questions/30172605/how-do-i-get-into-a-docker-containers-shell#comment75385171_30172605 https://stackoverflow.com/questions/22049212/copying-files-from-docker-container-to-host#22050116
to list running container:
sudo docker ps
to list all container:
docker ps -a
source: https://docs.docker.com/engine/reference/commandline/ps/
Running docker daemon behind proxy can lead to problem like failing to download image. To solve that we need to add the proxy to docker daemon systemd service. First, we need to create a systemd directory for docker service:
sudo mkdir /etc/systemd/system/docker.service.d
Now we will create a file with a text editor and put the environment variables in that file:
sudo vim /etc/systemd/system/docker.service.d/http-proxy.conf
The content would look like this:
[Service] Environment="HTTP_PROXY=http://proxy.example.com:80/" Environment="HTTPS_PROXY=http://proxy.example.com:80/"
Now save the file and exit. To see the change in effect we need to flush changes in systemd and restart docker daemon:
sudo systemctl daemon-reload sudo systemctl restart docker
More details: Control Docker with systemd: HTTP/HTTPS proxy
to run a docker image as a container do the following:
docker run -d repository docker run -d repository:tag docker run -d image_id
two ways to do it 1. attach and exec.
sudo docker attach image_id #OR sudo docker attach repository #by Name
sudo docker exec -i -t image_id /bin/bash #OR sudo docker exec -i -t repository /bin/bash
to duplicate an image:
docker tag image new_image
we can put pause in between two commands for 60 seconds by putting the following in between those commands:
RUN sleep 60
source: https://forums.docker.com/t/how-to-delay-execution-of-next-line-in-dockefile/50022/2
to completely remove docker and all related file, first identify what installed package we have:
dpkg -l | grep -i docker
Then run the following:
sudo apt-get purge -y docker-engine docker docker.io docker-ce docker-ce-cli sudo apt-get autoremove -y --purge docker-engine docker docker.io docker-ce docker-ce-cli
Make sure the above commands has all the following packages from the dpkg -l command. If not add them at the end. The above commands will not remove images, containers, volumes, or user created configuration files on your host. If you wish to delete all images, containers, and volumes run the following commands:
sudo rm -rf /var/lib/docker sudo rm /etc/apparmor.d/docker sudo groupdel docker sudo rm -rf /var/run/docker.sock sudo rm -rf /etc/docker sudo rm -rf ~/.docker
Finally remove docker-compose:
sudo rm /usr/local/bin/docker-compose
to install tzdata without user interaction, put this in Dockerfile:
ARG DEBIAN_FRONTEND=noninteractive
to remove all images and containers:
docker rm $(docker ps -a -q) docker rmi -f $(docker images -q)
source: https://techoverflow.net/2013/10/22/docker-remove-all-images-and-containers/
to execute source command inside Dockerfile:
RUN /bin/bash -c "source /path/to/file"
to rebuild docker image with docker-compose:
docker-compose build -f /path/to/docker-compose.yml
to removed unused data:
docker system prune
source: https://docs.docker.com/engine/reference/commandline/system_prune/
to see log:
docker logs container_id
to stop a container gracefully with SIGTERM:
docker stop container_id
to kill a container with SIGKILL when it is stuck:
docker kill container_id
to run command inside a container:
docker exac -it container_id command
in compose either:
.env file
or:
environment: - key1=value1 - key2=value2
source: https://docs.docker.com/compose/environment-variables/
to use environment variables in docker run either:
docker run --env-file ./env.list ubuntu bash
or:
docker run -e "key1=value1" -e "key2=value2" ubuntu bash
source: https://docs.docker.com/engine/reference/run/#env-environment-variables https://stackoverflow.com/a/30494145/5350059
Warning
need to test
docker-compose pull docker-compose up -d
to use a custom configuration for nginx:
FROM nginx COPY more_web_nginx.conf /etc/nginx/conf.d/ RUN rm /etc/nginx/conf.d/default.conf COPY . /usr/share/nginx/html
to map docker container port to a specific interface on host:
docker run -p <interface IP>:<outside port>:<inside port> $REST_OF_THE_COMMAND
to give name to a image:
version: '3'
services:
# for an image already build just put container_name bellow image
db:
image: postgres:10.1-alpine
container_name: pg_db
# for an image we are building put container_name bellow build
web:
build:
context: .
dockerfile: Dockerfile
container_name: web_dev
source: How do I define the name of image built with docker-compose
to COPY as non root:
COPY --chown=<user>:<group> <hostPath> <containerPath>
sudo docker stop $(sudo docker ps -a -q); sudo docker rm $(sudo docker ps -a -q)
sudo docker rmi -f $(sudo docker images | grep "<none>" | awk "{print $3}")
update_docker_images() {
for iid in $(sudo docker images | awk 'FNR>1 {print $1 ":" $2}')
do
echo updating $iid...
sudo docker pull $iid
done
}
OR one-liner:
for iid in $(sudo docker images | awk 'FNR>1 {print $1 ":" $2}'); do echo updating $iid..; sudo docker pull $iid; done
sudo docker rmi -f $(sudo docker images | grep $string | awk '{print $3}')
sudo docker volume rm $(sudo docker volume ls -q)
to add persistent data volume for PostgreSQL:
postgres:
container_name: postgres
restart: always
image: postgres:latest
volumes:
- ./database:/var/lib/postgresql/data
ports:
- "5432:5432
While running docker-compose with sudo docker-compose doesn't get the host environment variables. The -E flag of the sudo command solves the problem:
sudo -E docker-compose up
source: https://forums.docker.com/t/docker-compose-not-seeing-environment-variables-on-the-host/11837/8
consider the following Dockerfile contains:
FROM ubuntu:18.04 ARG PACKAGE RUN apt update && apt install $PACKAGE
We need to supply a value for the PACKAGE variable in the build stage and to do that in the docker-compose.yml we will do:
version: '3'
services:
docker-installer:
image: docker-installer:v1
build:
context: .
dockerfile: Dockerfile
args:
- PACKAGE=docker-ce
ignore file from being coping to docker image while building with .dockerignore. Just put the file and directories to be ignored in the .dockerignore file lie:
# comment */temp* */*/temp* temp?
source: https://docs.docker.com/engine/reference/builder/#dockerignore-file
to build specific service image:
sudo docker-compose build $SERVICE_NAME
to start specific service:
sudo docker-compose up $SERVICE_NAME
to comment in a Dockerfile, use #:
# Everything on this line is a comment
More doc Dockerfile reference: Format
For the following Dockerfile:
FROM ubuntu:18.04 ARG PACKAGE RUN apt update && apt install $PACKAGE
Pass the build time arguments in docker build like this:
sudo docker build --build-arg PACKAGE=docker-ce .
The general format is:
sudo docker build --build-arg $KEY=$VALUE --build-arg $KEY1=$VALUE1 .
More doc docker build: Set build-time variables (--build-arg)
to use a variable inside a Dockerfile CMD, run it with sh:
CMD ["sh", "-c", "django-admin startproject $PROJECTNAME"] #OR CMD django-admin startproject $PROJECTNAME
this happens because node_modules directory is created during build time inside the container and root directory is mounted during run time and node_modules is not present in the host directory. to solve this we just need to do a one way mount of the node_modules directory:
volumes: - ./worker/:/worker/ - /worker/node_modules
Dockerfile:
FROM python:3 ENV PYTHONUNBUFFERED 1 RUN mkdir /code WORKDIR /code COPY requirements.txt /code/ RUN pip install -r requirements.txt COPY . /code/
docker-compose.yml with postgresql:
version: '3'
services:
db:
image: postgres
web:
build: .
command: python manage.py runserver 0.0.0.0:8000
volumes:
- .:/code
ports:
- "8000:8000"
depends_on:
- db
docker-compose.yml without postgresql:
version: '3'
services:
web:
build: .
command: python manage.py runserver 0.0.0.0:8000
volumes:
- .:/code
ports:
- "8000:8000"
Dockerfile:
FROM ruby:2.5 RUN apt-get update -qq && apt-get install -y nodejs postgresql-client RUN mkdir /myapp WORKDIR /myapp COPY Gemfile /myapp/Gemfile COPY Gemfile.lock /myapp/Gemfile.lock RUN bundle install COPY . /myapp # Add a script to be executed every time the container starts. COPY entrypoint.sh /usr/bin/ RUN chmod +x /usr/bin/entrypoint.sh ENTRYPOINT ["entrypoint.sh"] EXPOSE 3000 # Start the main process. CMD ["rails", "server", "-b", "0.0.0.0"]
The entrypoint script, entrypoint.sh is used to fix a Rails-specific issue that prevents the server from restarting when a certain server.pid file pre-exists. This script will be executed every time the container gets started. entrypoint.sh:
#!/bin/bash set -e # Remove a potentially pre-existing server.pid for Rails. rm -f /myapp/tmp/pids/server.pid # Then exec the container's main process (what's set as CMD in the Dockerfile). exec "$@"
docker-compose.yml with postgresql:
version: '3'
services:
db:
image: postgres
volumes:
- ./tmp/db:/var/lib/postgresql/data
web:
build: .
command: bash -c "rm -f tmp/pids/server.pid && bundle exec rails s -p 3000 -b '0.0.0.0'"
volumes:
- .:/myapp
ports:
- "3000:3000"
depends_on:
- db
Dockerfile:
FROM node:7.7.2-alpine WORKDIR /usr/app COPY package.json . RUN npm install COPY . .
docker-compose.yml with postgresql:
version: '2'
services:
web:
build: .
command: npm run dev
volumes:
- .:/usr/app/
- /usr/app/node_modules
ports:
- "3000:3000"
depends_on:
- postgres
environment:
DATABASE_URL: postgres://todoapp@postgres/todos
postgres:
image: postgres:9.6.2-alpine
environment:
POSTGRES_USER: todoapp
POSTGRES_DB: todos
docker-compose.yml without postgresql:
version: '2'
services:
web:
build: .
command: npm run dev
volumes:
- .:/usr/app/
- /usr/app/node_modules
ports:
- "3000:3000"
source: https://rollout.io/blog/using-docker-compose-for-nodejs-development/
to load a pgsql dump file to db:
sudo docker exec postgres psql -U postgres my_db_name < dump.sql