how to use networking when building docker-compose?

Question

i want to build a docker image of my app. the build process (tests) requires other services (db). seems like my app can't connect to the db

i managed to replicate the problem using simple and small images.

dockerfile (it just tries to reach web endpoint)

from alpine:3.10.2
run wget web:8080
cmd ["sh"]

docker-compose

version: "3.7"
services:
  web:
    image: tutum/hello-world
    ports:
      - "8080:80"
  app:
    build: .
    depends_on:
      - web

during docker-compose up i got

wget: bad address 'web:8080'
ERROR: Service 'app' failed to build: The command '/bin/sh -c wget web:8080' returned a non-zero code: 1

how can i access other container during build process?

Answer 1

you need to use network as host in your compose:

build:
     network: host

and access it using localhost:port

Example:

docker-compose:

version: "3.7"
services:
  web:
    image: tutum/hello-world
    ports:
      - "8080:80"
  app:
    build:
     context: .
     network: host
    depends_on:
      - web

Dockerfile:

FROM alpine:3.10.2
RUN wget localhost:8080
CMD ["sh"]

run web:

docker-compose up -d --build web

run app:

docker-compose up -d --build app

output:

Building app
Step 1/3 : FROM alpine:3.10.2
3.10.2: Pulling from library/alpine
9d48c3bd43c5: Pull complete
Digest: sha256:72c42ed48c3a2db31b7dafe17d275b634664a708d901ec9fd57b1529280f01fb
Status: Downloaded newer image for alpine:3.10.2
 ---> 961769676411
Step 2/3 : RUN wget localhost:8080
 ---> Running in f021283ab323
Connecting to localhost:8080 (127.0.0.1:8080)
index.html           100% |********************************|   478  0:00:00 ETA
Removing intermediate container f021283ab323
 ---> aae07c08a119
Step 3/3 : CMD ["sh"]
 ---> Running in e81d9401db71
Removing intermediate container e81d9401db71
 ---> 6c217a535c7d

Successfully built 6c217a535c7d
Successfully tagged docker-test_app:latest
docker-test_web_1 is up-to-date
Creating docker-test_app_1 ... done