Interpreted variables in environment variables

[bluk]

The Constraint section in the Job Specification has a table with interpreted variables such as $node.id and $meta.<key>. I assume the interpreted variables are meant for just constraints but I want to use them in other parts of the config.

For my use case, I've added some host machine unique metadata to the Nomad client's meta configuration and want to pass that onto a task.

I tried using them in in a task's env section like:

env {
  MY_ENV_NAME = "$node.id"
}

However, the value is set to the literal string $node.id (so not interpreted).

Is there some way to do this? Thanks!

[cbednarski]

@bluk Thanks for opening an issue. This is currently supported only in a limited capacity. We'd like to expand this in a future release.

So we can design and implement this correctly can you describe your use case? For example, I know one use-case is to configure docker container networking via container:<id-of-container-with-networking>. Can you describe what you're trying to do with $node.id?

[bluk]

@cbednarski Actually I'm trying to use the Nomad's client meta (used $node.id as a simpler example). Sorry for the misleading example.

I am putting a unique UUID for Vault to use in Nomad's client meta configuration. Then I was hoping to use $meta.uuid to have the variable interpreted by Nomad when the task was run. When a Docker container is run, it would be passed the UUID as an environment variable, and I could use the Auth Backend: App ID to lookup some credentials.

[cbednarski]

@bluk I see. So to clarify, you want to pass a value based on which node the job is placed on?

Thanks for highlighting that use case! I think we can improve this. What I would recommend for now is putting a file on the filesystem on that machine, which you can read in your exec or mount into a container.

[bluk]

@cbednarski Yes, exactly! :)

Forgive my ignorance, but how do you mount an arbitrary filesystem into your container via Nomad? I didn't see any way to do that in the documentation.

[cbednarski]

@bluk Ah that's a good question. We don't actually support this yet. Sorry to mislead you about this!

[macb]

For the new system type it would be nice to gather some information for common application configuration, such as hostname or ip. This would be equally useful as args for the fork/exec drivers.

[github-actions]

I'm going to lock this issue because it has been closed for 120 days ⏳. This helps our maintainers find and focus on the active issues.
If you have found a problem that seems similar to this, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.