Specify that - is replaced by _ when changing meta keys into environment variables

[Kamilcuk]

On the documentation page https://developer.hashicorp.com/nomad/docs/runtime/environment#meta it is not explained that meta keys have replaced - for _ when transformed into environment variables. Although variables with - in the name can't be accessed with unix shell, they are technically perfectly valid environment variable names. I tried to follow the source code https://github.com/hashicorp/nomad/blob/main/client/taskenv/env.go#L115 but with no success.

Proposal

Please specify in the documentation that meta keys containing - are replaced by _ when transformed into environment variables.

Please also specify if other characters are replaced? Do all non-alphanumeric characters in meta keys are replaced by underscores?

Use-cases

Currently, this behavior I believe would count as "unspecified". Or it is specified in the documentation, but I have not found it, that's on me.

Attempted Solutions

job "test_meta_dash" {
  datacenters = [
    "wee-dev",
  ]
  type = "service"
  namespace = "dev"
  meta {
    key-key = "value"
  }
  group "test" {
    task "test" {
      driver = "docker"
      config {
        image = "busybox"
        command = "sh"
        args = [
          "-xc",
          "env | grep NOMAD_META_"
        ]
      }
    }
  }
}

outputs:

NOMAD_META_KEY_KEY=value
NOMAD_META_key_key=value

The environment variable is NOMAD_META_key_key not NOMAD_META_key-key.

[tgross]

Hi @Kamilcuk! This definitely needs better documentation. We should probably also update the docs for the meta block. I'll mark this for fixing but if you're interested in opening a PR with the fix I'd be happy to review it as well.

In the meantime, the code that calls this is in taskenv/env.go#L611-L622, and it "cleans" any of the Nomad-owned environment variable paths. That CleanEnvVar function removes anything that isn't in [A-Za-z0-9_\.]. This was introduced in #2405

[Kamilcuk]

Amazing, thank you for code links and clarification.

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