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up vote 1 down vote favorite

I'm building a container for a ruby app. My app's configuration is contained within environment variables (loaded inside the app with dotenv).

One of those configuration variables is the public ip of the app, which is used internally to make links. I need to add a dnsmasq entry pointing this ip to 127.0.0.1 inside the container, so it can fetch the app's links as if it were not containerized.

I'm therefore trying to set an ENV in my Dockerfile which would pass an environment variable to the container.

I tried a few things.

ENV REQUEST_DOMAIN $REQUEST_DOMAIN
ENV REQUEST_DOMAIN `REQUEST_DOMAIN`

Everything passes the "REQUEST_DOMAIN" string instead of the value of the environment variable though. Is there a way to pass environment variables values from the host machine to the container?

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3 Answers

up vote 1 down vote

So you can do: cat Dockerfile | envsubst | docker build -t my-target -

Then have a Dockerfile with something like:

ENV MY_ENV_VAR $MY_ENV_VAR

I guess there might be a problem with some special characters, but this works for most cases at least.

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up vote 0 down vote accepted

This was in fact related to the -dns issue in docker 0.6.
With this version of docker, resolving dns is broken, and we need to explicitely provide a dns server.

sudo docker run -dns 8.8.8.8

Solved the issue with me.

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up vote -1 down vote

add -e key for passing environment variables to container. example:

$ MYSQLHOSTIP=$(sudo docker inspect -format="{{ .NetworkSettings.IPAddress }}" $MYSQL_CONRAINER_ID)
$ sudo docker run -e DBIP=$MYSQLHOSTIP -i -t myimage /bin/bash

root@87f235949a13:/# echo $DBIP
172.17.0.2
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