How to link docker containers on build?

Question

I linked my app container to postgres on run:

docker run --link postgres:postgres someproject/develop

and it worked fine.

Answer 1

I had a similar issue. I wanted to speed up image builds with the help of apt-cacher. It runs in its own container and somehow other images, which I built, had to communicate with it.

The solution was to publish apt-cacher port on all interfaces. This includes e.g. docker0, which is available to intermediate containers spawned during image build.

Example Dockerfile:

FROM debian:8

RUN ping -c 2 172.17.0.1

And this is how it builds:

$ docker build -  47af6ca8a14a
Step 2 : RUN ping -c 2 172.17.0.1
 ---> Running in 4f56ce7c7b63
PING 172.17.0.1 (172.17.0.1): 56 data bytes
64 bytes from 172.17.0.1: icmp_seq=0 ttl=64 time=0.117 ms
64 bytes from 172.17.0.1: icmp_seq=1 ttl=64 time=0.130 ms
--- 172.17.0.1 ping statistics ---
2 packets transmitted, 2 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.117/0.123/0.130/0.000 ms
 ---> 5c73a36a0a6a
Removing intermediate container 4f56ce7c7b63