CODEWITHSUNDEEP
docker
Sabbane
Sabbane

Reputation: 3316

Is it possible to customize environment variable by linking two docker containers?

I've created a docker image for my database server and one for the web application. Using the documentation I'm able to link between both container using the environment variables as follow:

value="jdbc:postgresql://${DB_PORT_5432_TCP_ADDR}:${DB_PORT_5432_TCP_PORT}/db_name"

It works fine now but it would be better that the environment variables are more general and without containing a static port number. Something like:

value="jdbc:postgresql://${DB_URL}:${DB_PORT}/db_name"

Is there anyway to link between the environment variables? for example by using the ENV command in the dockerfile ENV DB_URL=$DB_PORT_5432_TCP_ADDR or by using the argument --env by running the image docker run ... -e DB_URL=$DB_PORT_5432_TCP_ADDR docker_image ?

Upvotes: 4

Views: 531

Answers (1)

L0j1k
L0j1k

Reputation: 12645

Without building this kind of functionality into your docker startup shell scripts or other orchestration mechanism, this is not possible at the moment to create environment variables like you are describing here. You do mention a couple of workarounds. However, the problem at least with using the -e DB_URL=... in your docker run command is that your $DB_PORT_5432_TCP_ADDR environment variable is not known at runtime, and so you will not be able to set this value when you run it. Typically, this is what your orchestration layer is used for, service discovery and passing this kind of data among your containers. There is at least one workaround mentioned here on SO that involves constructing a special shell script that you put in your CMD or ENTRYPOINT directives that passes the environment variable to the container.

Upvotes: 3

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