Building images in Compose in Docker - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the build key in a Docker Compose file?

The build key tells Docker Compose to create a Docker image from a Dockerfile before starting the container.

intermediate

How do you specify the path to a Dockerfile in a Compose file?

Use build: with a context for the folder and dockerfile for the file name, like:<br>

build:
  context: ./app
  dockerfile: Dockerfile.dev

beginner

What happens if you run docker-compose up and the image does not exist?

Docker Compose will automatically build the image using the Dockerfile specified under the build key before starting the container.

intermediate

Can you pass build arguments in Docker Compose? How?

Yes, you can pass build arguments using the args key under build. For example:<br>

build:
  context: .
  args:
    VERSION: 1.0

beginner

What is the difference between image and build in a Compose service?

image specifies an existing image to use, while build tells Compose to create an image from a Dockerfile before running the container.

In a Docker Compose file, which key is used to build an image from a Dockerfile?

A build

B image

C container

D service

The build key tells Compose to build an image from a Dockerfile.

How do you specify a custom Dockerfile name in Compose?

A Rename the Dockerfile to Dockerfile.compose

B Use <code>file</code> key at root

C Under <code>build</code>, use <code>dockerfile</code> key

D Use <code>image</code> key with filename

You specify the Dockerfile name with the dockerfile key inside the build section.

What does Docker Compose do if the image specified in image does not exist locally and no build is defined?

A Builds the image automatically

B Pulls the image from Docker Hub

C Throws an error and stops

D Creates an empty image

Docker Compose tries to pull the image from a registry like Docker Hub if it is not found locally.

Which command builds images defined in a Docker Compose file before starting containers?

A docker-compose up

B docker-compose run

C docker-compose start

D docker-compose build

docker-compose up builds images if needed and starts containers.

How can you pass build-time variables to a Dockerfile using Compose?

A Using <code>params</code> under <code>service</code>

B Using environment variables under <code>environment</code>

C Using <code>variables</code> key at root

D Using <code>args</code> under <code>build</code>

Build arguments are passed with the args key inside the build section.

Explain how Docker Compose builds images using the build key and what options you can specify under it.

Think about how you tell Compose where the Dockerfile is and how to customize the build.

Describe the difference between using image and build in a Docker Compose service.

Consider when you want to use a ready image versus creating your own.