docker-compose reference YAML file with comments

docker-compose.yml

# https://docs.docker.com/compose/yml/
# Each service defined in docker-compose.yml must specify exactly one of
# image or build. Other keys are optional, and are analogous to their
# docker run command-line counterparts.
#
# As with docker run, options specified in the Dockerfile (e.g., CMD,
# EXPOSE, VOLUME, ENV) are respected by default - you don't need to
# specify them again in docker-compose.yml.
#
service_name:
  # Path to a directory containing a Dockerfile. When the value supplied
  # is a relative path, it is interpreted as relative to the location of
  # the yml file itself. This directory is also the build context that is
  # sent to the Docker daemon.
  # 
  # Compose will build and tag it with a generated name, and use that image
  # thereafter.
  build: ./
  # Add or drop container capabilities. See man 7 capabilities for a full list.
  cap_add:
    - ALL
  cap_drop:
    - NET_ADMIN
    - SYS_ADMIN
  # Override the default command.
  command: /usr/bin/start
  # A single value, analogous to its docker run counterpart.
  cpu_shares: 73
  # A single value, analogous to its docker run counterpart.
  domainname: foo.com
  # Custom DNS servers. Can be a single value or a list.
  #
  # dns: 8.8.8.8
  dns:
    - 8.8.8.8
    - 9.9.9.9
  # Custom DNS search domains. Can be a single value or a list.
  #
  # dns_search: example.com
  dns_search:
    - dc1.example.com
    - dc2.example.com
  # A single value, analogous to its docker run counterpart.
  entrypoint: /code/entrypoint.sh
  # Add environment variables from a file. Can be a single value or a list.
  #
  # If you have specified a Compose file with docker-compose -f FILE, paths
  # in env_file are relative to the directory that file is in.
  #
  # Environment variables specified in environment override these values.
  #
  # Compose expects each line in an env file to be in VAR=VAL format. Lines
  # beginning with # (i.e. comments) are ignored, as are blank lines.
  #
  # env_file: .env
  env_file:
    - ./common.env
    - ./apps/web.env
    - /opt/secrets.env
  # Add environment variables. You can use either an array or a dictionary.
  #
  # Environment variables with only a key are resolved to their values on
  # the machine Compose is running on, which can be helpful for secret or
  # host-specific values.
  #
  # environment:
  #   - RACK_ENV=development
  #   - SESSION_SECRET
  environment:
    RACK_ENV: development
    SESSION_SECRET:
  # Expose ports without publishing them to the host machine - they'll only
  # be accessible to linked services. Only the internal port can be specified.
  expose:
    - "3000"
    - "8000"
  # Extend another service, in the current file or another, optionally
  # overriding configuration.
  extends:
    file: common.yml
    service: webapp
  # Link to containers started outside this docker-compose.yml or even
  # outside of Compose, especially for containers that provide shared or
  # common services. external_links follow semantics similar to links when
  # specifying both the container name and the link alias (CONTAINER:ALIAS).
  external_links:
    - redis_1
    - project_db_1:mysql
    - project_db_1:postgresql
  # A single value, analogous to its docker run counterpart.
  hostname: foo
  # Tag or partial image ID. Can be local or remote - Compose will
  # attempt to pull if it doesn't exist locally.
  image: centos/centos7
  # Link to containers in another service. Either specify both the service
  # name and the link alias (SERVICE:ALIAS), or just the service name
  # (which will also be used for the alias).
  #
  # An entry with the alias' name will be created in /etc/hosts inside
  # containers for this service.
  #
  # Each linked container injects a set of environment variables, each of
  # which begins with the uppercase name of the container.
  #
  # To see what environment variables are available to a service, run
  # docker-compose run SERVICE env.
  #
  # * name_PORT
  #   Full URL, e.g. DB_PORT=tcp://172.17.0.5:5432
  #
  # * name_PORT_num_protocol
  #   Full URL, e.g. DB_PORT_5432_TCP=tcp://172.17.0.5:5432
  #
  # * name_PORT_num_protocol_ADDR
  #   Container's IP address, e.g. DB_PORT_5432_TCP_ADDR=172.17.0.5
  #
  # * name_PORT_num_protocol_PORT
  #   Exposed port number, e.g. DB_PORT_5432_TCP_PORT=5432
  #
  # * name_PORT_num_protocol_PROTO
  #   Protocol (tcp or udp), e.g. DB_PORT_5432_TCP_PROTO=tcp
  #
  # * name_NAME
  #   Fully qualified container name, e.g. DB_1_NAME=/myapp_web_1/myapp_db_1
  links:
    - db
    - db:database
    - redis
  # A single value, analogous to its docker run counterpart.
  mem_limit: 1000000000
  # Networking mode. Use the same values as the docker client --net parameter.
  #
  # net: "bridge"
  # net: "none"
  # net: "container:[name or id]"
  # net: "host"
  net: "bridge"
  # Sets the PID mode to the host PID mode. This turns on sharing between
  # container and the host operating system the PID address space. Containers
  # launched with this flag will be able to access and manipulate other
  # containers in the bare-metal machine's namespace and vise-versa.
  pid: "host"
  # Expose ports. Either specify both ports (HOST:CONTAINER), or just the
  # container port (a random host port will be chosen).
  #
  # Note: When mapping ports in the HOST:CONTAINER format, you may experience
  # erroneous results when using a container port lower than 60, because YAML
  # will parse numbers in the format xx:yy as sexagesimal (base 60). For this
  # reason, we recommend always explicitly specifying your port mappings as
  # strings.
  ports:
    - "3000"
    - "8000:8000"
    - "49100:22"
    - "127.0.0.1:8001:8001"
  # A single value, analogous to its docker run counterpart.
  privileged: true
  # A single value, analogous to its docker run counterpart.
  restart: always
  # A single value, analogous to its docker run counterpart.
  stdin_open: true
  # A single value, analogous to its docker run counterpart.
  tty: true
  # A single value, analogous to its docker run counterpart.
  user: postgresql
  # Mount paths as volumes, optionally specifying a path on the host machine
  # (HOST:CONTAINER), or an access mode (HOST:CONTAINER:ro).
  volumes:
    - /var/lib/mysql
    - cache/:/tmp/cache
    - ~/configs:/etc/configs/:ro
  # Mount all of the volumes from another service or container.
  volumes_from:
    - service_name
    - container_name
  # A single value, analogous to its docker run counterpart.
  working_dir: /code