What is the difference between `docker-compose build` and `docker build`?

Question

What is the difference between docker-compose build and docker build?

Suppose in a dockerized project path there is a docker-compose.yml file:

docker-compose build

And

docker build

Answer 1

docker-compose can be considered a wrapper around the docker CLI (in fact it is another implementation in python as said in the comments) in order to gain time and avoid 500 characters-long lines (and also start multiple containers at the same time). It uses a file called docker-compose.yml in order to retrieve parameters.

You can find the reference for the docker-compose file format here.

So basically docker-compose build will read your docker-compose.yml, look for all services containing the build: statement and run a docker build for each one.

Each build: can specify a Dockerfile, a context and args to pass to docker.

To conclude with an example docker-compose.yml file :

version: '3.2'

services:
  database:
    image: mariadb
    restart: always
    volumes:
      - ./.data/sql:/var/lib/mysql

  web:
    build:
      dockerfile: Dockerfile-alpine
      context: ./web
    ports:
      - 8099:80
    depends_on:
      - database 

When calling docker-compose build, only the web target will need an image to be built. The docker build command would look like :

docker build -t web_myproject -f Dockerfile-alpine ./web

Answer 2

docker-compose build will build the services in the docker-compose.yml file.

https://docs.docker.com/compose/reference/build/

docker build will build the image defined by Dockerfile.

https://docs.docker.com/engine/reference/commandline/build/

Answer 3

Basically, docker-compose is a better way to use docker than just a docker command.

If the question here is if docker-compose build command, will build a zip kind of thing containing multiple images, which otherwise would have been built separately with usual Dockerfile, then the thinking is wrong.

Docker-compose build, will build individual images, by going into individual service entry in docker-compose.yml.

With docker images, command, we can see all the individual images being saved as well.

The real magic is docker-compose up.

This one will basically create a network of interconnected containers, that can talk to each other with name of container similar to a hostname.

Answer 4

Adding to the first answer...

You can give the image name and container name under the service definition.

e.g. for the service called 'web' in the below docker-compose example, you can give the image name and container name explicitly, so that docker does not have to use the defaults.

Otherwise the image name that docker will use will be the concatenation of the folder (Directory) and the service name. e.g. myprojectdir_web

So it is better to explicitly put the desired image name that will be generated when docker build command is executed.

e.g. image: mywebserviceImage container_name: my-webServiceImage-Container

example docker-compose.yml file :

version: '3.2'
services:
  web:
    build:
      dockerfile: Dockerfile-alpine
      context: ./web
    ports:
      - 8099:80
    image: mywebserviceImage
    container_name: my-webServiceImage-Container
    depends_on:
      - database

Answer 5

Few additional words about the difference between docker build and docker-compose build. Both have an option for building images using an existing image as a cache of layers.

• with docker build, the option is --cache-from <image>
• with docker-composer, there is a tag cache_from in the build section.

Unfortunately, up until now, at this level, images made by one are not compatible with the other as a cache of layers (Ids are not compatible). However, docker-compose v1.25.0 (2019-11-18), introduces an experimental feature COMPOSE_DOCKER_CLI_BUILD so that docker-compose uses native docker builder (therefore, images made by docker build can be used as a cache of layers for docker-compose build)