It is documented that 'value' has default "" but it does not work

[EugenKon]

Nomad version

1.8.2

Operating system and Environment details

Ubuntu 22.04

Issue

[....] Error during plan: Unexpected response code: 500 (1 error occurred:
[....] 	* Task group wi-api-group validation failed: 1 error occurred:
[....] 	* Task prepare-credentials-task validation failed: 1 error occurred:
[....] 	* Affinity 1 validation failed: 1 error occurred:
[....] 	* Operator "=" requires an RTarget)

https://developer.hashicorp.com/nomad/docs/job-specification/affinity#value

Even manual value="" does not help.

Reproduction steps

      affinity {
        attribute = "${node.unique.id}"
        weight    = -50
      }

Expected Result

No error should occur

Actual Result

Error happened

[gulducat]

Hey there @EugenKon, thanks for reaching out.

The requirements for value depends on which operator is being used.

The default operator = requires a non-empty value, as indicated in the error message Operator "=" requires an RTarget. Admittedly, it's not obvious that RTarget means value. Perhaps we could improve the documentation here.

A value of "" is technically valid, for example, if operator = "regexp" (although it would effectively match everything, so wouldn't be much of an affinity). If you wanted to accomplish your example, where apparently node.unique.id = "", then I believe this would work:

affinity {
    attribute = "${node.unique.id}"
    operator  = "regexp"
    value     = "^$"
}

However in Nomad there is no such thing as an empty Node ID, so this seems pretty odd.

I don't believe we should change the code so that = would work with "", unless you have a specific attribute that would benefit from that, but perhaps we can improve the documentation. Does my explanation make sense to you? Do you have any suggestions for how we might better communicate this in the documentation?

[EugenKon]

I agree with you that everything here is about more meaningfull error messages and the documentation.
Thanks