CODEWITHSUNDEEP
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meallhour
meallhour

Reputation: 15591

Difference between 'image' and 'build' within docker compose

Please help me understand the difference between 'image' and 'build' within docker compose

Upvotes: 77

Views: 32195

Answers (3)

Trevor Arnold
Trevor Arnold

Reputation: 196

Official documentation that goes in depth on the difference between build and image might be of some help here. https://docs.docker.com/compose/compose-file/build/ Long story short, build needs the path to a Dockerfile that it can use to build an image, but image goes to a repository to grab an existing image. Both can be included for a service, but

When a service definition includes both the image attribute and a build section, the Compose implementation can’t guarantee a pulled image is strictly equivalent to building the same image from source. Without any explicit user directives, the Compose implementation with Build support MUST first try to pull the image, then build from source if the image was not found on registry. The Compose implementation MAY offer options to customize this behaviour by user request.

Upvotes: 7

Shahid Hussain
Shahid Hussain

Reputation: 1789

build: expects dockerfile path as an argument, it will build an image first and then use the image to create a container.

image: expects existing image name as argument , it will launch container using this image.

Example:docker-compose.yaml

version: '3'
services:
  service1:
    build: .
    ports:
      - "5000:5000"
  service2:
    image: "redis:alpine"

service1 will build an image first based on Dockerfile of current path and run container based on this image.

service2 will download "redis:alpine" image from docker hub and run container on downloaded image.

Upvotes: 9

VonC
VonC

Reputation: 1325966

  • image means docker compose will run a container based on that image
  • build means docker compose will first build an image based on the Dockerfile found in the path associated with build (and then run a container based on that image).

PR 2458 was eventually merged to allow both (and use image as the image name when building, if it exists).

therobyouknow mentions in the comments:

dockerfile: as a sub-statement beneath build: can be used to specify the filename/path of the Dockerfile.

version: '3'
services:
  webapp:
    build:
      context: ./dir
      dockerfile: Dockerfile-alternate
      args:
        buildno: 1

Upvotes: 72

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