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How to pass container ip as ENV to another container in dockerfile file

This is my docker-compose file:

version: '3.0'
services:
 app-web:
  restart: always
  build: ./web
  environment:
    PG_HOST: $(APP_DB_IP)
    PG_PORT: 5432
  ports:
   - "8081:8080"
  links: 
   - app-db

 app-db:
  build: ./db
  expose: 
   - "5432"

  volumes:
   - /var/lib/postgresql/data

I want to pass app-web ip app-db (Postgresql in this case) as ENV var so that it can connect to DB normally ... any idea on how to achieve it?

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2 answers


You can use app-db as name instead of ip, docker will automatically detect that the ip is correct. As stated in the Docker docs: A container can always discover other containers on the same stack using only the container name as the hostname.

So, in your example, you can use:



environment:
    PG_HOST: app-db

Source: https://docs.docker.com/docker-cloud/apps/service-links/#discovering-containers-on-the-same-service-or-stack

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You don't really need to do anything as you are already using the function links

in Docker Compose. Just get rid of the variable PG_HOST

and use the hostname app-db

:

services:
 app-web:
  restart: always
  build: ./web
  environment:
    PG_PORT: 5432
  ports:
   - "8081:8080"
  links: 
   - app-db

Since you included the entry app-db

in links

, you can simply use app-db

as the hostname in your container app-web

. Docker will set up a hostname mapping in the container app-web

, which resolves the hostname app-db

to the IP address of the database container.

You can test by doing the following, which will try to ping the container app-db

from the container app-web

:

docker-compose exec app-web bash -c "ping app-db"


This should show the output of the ping command showing the resolved IP address of the container app-db

, for example:

PING app-db (172.19.0.2): 56 data bytes
64 bytes from 172.19.0.2: icmp_seq=0 ttl=64 time=0.055 ms
64 bytes from 172.19.0.2: icmp_seq=1 ttl=64 time=0.080 ms
64 bytes from 172.19.0.2: icmp_seq=2 ttl=64 time=0.098 ms

Click ctrl+c

to stop ping command.

As shown in the other answer, if you still want to pass in the hostname (which is probably a good idea, just in case you want to specify a different database), you can simply use app-db

as a value:

services:
 app-web:
  restart: always
  build: ./web
  environment:
    PG_HOST: app-db
    PG_PORT: 5432
  ports:
   - "8081:8080"
  links: 
   - app-db
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