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

Question

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

Answer 1

• 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 

Answer 2

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.