Add ability to read environment variables from a local file

[mildred]

Currently, I have a nomad job running a docker container where some of the environment variables are generated using a nomad template. This is very useful to generate some of the environment variables from consul keys.

Currently, I'm overriding the run command with a sh -c command running a oneliner script. This works for this particular use case but it won't work for every docker image.

What would be nice is to have a possibility to define a list of files containing environment variables that would be read before running the task.

My current job looks like:

task "web" {
  driver = "docker"
  config {
    command = "sh"
    args = [
      "-c",
      "exec 2>&1; . /local/env; env | sort; exec bundle exec rails server -b 0.0.0.0"
    ]
    ...
  }

  ...

  template {
    destination = "local/env"
    data = <<TEMPLATE
export PROJECT_SERVER_URL=http://local-{{key_or_default "squarescale-web/forward-address" ""}}
TEMPLATE
  }
}

I'd prefer something like:

task "web" {
  driver = "docker"

  ...

  environment_files = [ "local/env" ]

  template {
    destination = "local/env"
    data = <<TEMPLATE
PROJECT_SERVER_URL=http://local-{{key_or_default "squarescale-web/forward-address" ""}}
TEMPLATE
  }
}

[schmichael]

Great minds think alike! #2654 is almost ready and adds almost exactly the behavior you're asking for. The one difference is that instead of the environment_files=[...] key there's an env=true flag on each template you want to read in as an environment variable.

It will be in master soon and released in 0.6.

Closing this as a dupe of #1765 as that's the original inspiration for this feature.

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