Docker Compose Cheatsheet
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Table Of Contents
Docker Compose File
Compose is a tool for defining and running multi-container Docker applications. It utilizes a
YAML configuration file (usually called docker-compose.yml) to specify the services and how to
launch them.
One can find the official documentation for Docker Compose online.
Example Configuration File
This is a sample docker-compose.yml configuration that should hopefully help get you started.
It is easier to remove things than to find what to add.
version: "3"
networks:
backend:
driver: bridge
services:
app:
build:
context: .
dockerfile: Dockerfile
container_name: app
image: ${REGISTRY}/my-project-name
restart: always
ports:
- "80:80"
- "443:443"
depends_on:
- db
networks:
- backend
env_file:
- ./.env
db:
image: mariadb:10.5
container_name: db
restart: always
networks:
backend
volumes:
- mysql-data:/var/lib/mysql
environment:
- FOO=bar
- SOME_ENV_VAR=${SUBSTITUTED_VARIABLE}
env_file:
- ./.env
volumes:
mysql-data:
driver: local
Volumes
Named Volumes
If your container just needs to persistently store state that it generates, then named volumes are great. You can use named volumes like so:
version: "3"
services:
db:
image: mariadb:10.5
container_name: db
volumes:
- my-volume-name:/var/lib/mysql
volumes:
my-volume-name:
driver: local
Specifying Hosts
If you need to manually pass DNS records to your containers (becuase updating your local
server's /etc/hosts file won't work), then you can do that like so:
extra_hosts:
- "subdomain.mydomain.org:192.168.1.123"
e.g.
services:
kibana:
image: docker.elastic.co/kibana/kibana:7.9.0
extra_hosts:
- "elastic-search.programster.org:192.168.1.123"
Restart Choices
If you specify no for your restart (which you don't actually need to do because it's the
default), then be aware that it is the only value you need to wrap in quotation marks.
The choices are:
"no"alwayson-failureunless-stopped
Disable Logging
If you want to disable output from one of the services, just set the logging driver to none,
like so:
mysql:
image: mysql:5.6
restart: "no"
logging:
driver: none
Commands
Launch Everything
Start all the containers/services using docker-compose
docker-compose up
Start A Specific Service
Sometimes one needs to only start a specific service, or manually start the services in order to start them in the correct order. E.g. it's nice to start your database service first so it's ready when your application starts.
docker-compose up $SERVICE_NAME
Specify Docker Compose File
docker-compose will use a file called docker-compose.yml by default, but if you want to use a
different file, you can specify its path.
docker-compose -f /path/to/file.yml up
Execute Command In A Running Service
The following can be used to run a command against a service (not the name of the container).
docker-compose exec $SERVICE_NAME /command/to/run param1
e.g.
docker-compose exec web php artisan october:up
Specify Compose File
Specify a custom filepath for your docker-compose file (it assumes docker-compose.yml in your
current directory by default)
docker-compose -f custom-docker-compose.yml up
Apply multiple compose files (changes in latter)
docker-compose -f docker-compose.yml docker-compose-production.yml
Re-deploy just one service. Particularly useful after a rebuild.
docker-compose up $SERVICE_NAME
Environment Variables
There are many ways to pass environment variables to your container through the use of docker-compose.
Individually Inside The Docker Compose File
Firstly, you can manually specify them individually like so:
version: "3"
services:
app:
image: my-docker-image
environment:
- MY_VARIABLE_NAME="bob"
ports:
- "80:80"
docker-compose.yml file as
part of your source control.
Implicit .env File
You can have a .env file at the same location as your docker-compose file. All variables within
this .env file will automatically be used by docker-compose.
docker-compose.yml file, or path of where
we are calling docker-compose from which may be different). E.g If one was to run
docker-compose -f /path/to/docker-compose.yml up.
Specify Env File For Docker Compose
docker-compose --env-file ./config/.env up
Specify .env File In Compose File
Use the .env_file declaration as part of your configuration to specify where the .env file is
that you wish to use.
version: "3"
services:
app:
container_name: app
image: my-image-name
env_file:
- ./path/to/.env
ports:
- "80:80"
Variables In Compose File
If you need to use a variable in the docker-compose file, use the ${VARIABLE_NAME} syntax and
provide the VARIABLE_NAME through either an environment variable, or an ARG (details of
the many various ways of providing environment variables and arguments detailed above).
For example, the configuration below will use environment or ARG variables to build the image
declaration using the DOCKER_REGISTRY, PROJECT_NAME, AND TAG_VERSION variables.
version: "3"
services:
app:
build:
context: .
dockerfile: ./Dockerfile
container_name: app
image: ${DOCKER_REGISTRY}/${PROJECT_NAME}:${TAG_VERSION}
restart: always
ports:
- "80:80"
Docker Compose Variables
Compose Project Name
It's worth setting the COMPOSE_PROJECT_NAME environment variable for specifying what I call the
"namespace" of your project. This will add prefixes, to try and prevent generic names for
things like your volumes, clashing with other projects. E.g. if you have two projects that use
a MySQL volume called "mysql-data", you wouldn't want them to both reference the same volume.
If you don't set this variable, prefixes will be based on the folder name of where your
docker-compose.yml file is.
You can also manually specify the project name as a parameter when calling docker-compose like so:
docker-compose --project-name "my-project-name` up
...or:
docker-compose -p "my-project-name` up
Build Arguments
References
- Stack Overflow - How can you make the docker container use the host machine's /etc/hosts file?
- vsupalov.com - Docker ARG vs ENV
- Stack Overflow - Disable logging for one container in Docker-Compose
First published: 23rd August 2020