Service definition

Add a web service to the compose file.

Service definition

A service can be created from a ready image (image:) or from a Dockerfile in the project (build:). Each docker run option has a Compose counterpart:

services:
  api:
    build: .
    image: api:dev
    ports:
      - "8000:8000"
    environment:
      LOG_LEVEL: info
    restart: unless-stopped

When build and image are written together, the built image is tagged with that name.

Build details

In long form, build can take the context, Dockerfile and build arguments. When the code changes, the image is rebuilt with --build:

services:
  api:
    build:
      context: ./api
      dockerfile: Dockerfile
      args:
        SURUM: "1.0.0"

docker compose up -d --build

Compose uses the project folder's name (or -p) as a prefix: the container name becomes proje-api-1.

Exercise The API service

Write the api service in compose.yaml: built from the current folder (build: .); publishing port 8000 with the same number; LOG_LEVEL: info under environment; restart: unless-stopped.

Show example solution

# compose.yaml
services:
  api:
    build: .
    ports:
      - "8000:8000"
    environment:
      LOG_LEVEL: info
    restart: unless-stopped

Test yourself

What is the Compose counterpart of the docker run -e LOG_LEVEL=info option?
- args: LOG_LEVEL=info
- LOG_LEVEL: info under environment
- env: LOG_LEVEL
- vars: [info]
Show answer

LOG_LEVEL: info under environment — environment can be written both as a map and as a list (- NAME=value).
Create the service from the Dockerfile in the project.
```
services:
  api:
    ____: .
```
Show answer
```
services:
  api:
    build: .
```
Match the docker run counterparts.

-p 8000:8000

ports
-e NAME=value

environment
--restart

restart
docker build .

build: .

Next lesson: Database service

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