job plan output missing diff on scaling block

[tgross]

When a nomad job plan results in an update, the diff between the old and new is shown even if the update is an in-place update (one that doesn't replace the allocation). For example, and update to an update block looks like this:

$ nomad job plan httpd.nomad.hcl
+/- Job: "httpd"
+/- Task Group: "web" (1 in-place update)
  +/- Update {
        AutoPromote:      "false"
        AutoRevert:       "false"
        Canary:           "0"
        HealthCheck:      "checks"
        HealthyDeadline:  "300000000000"
    +/- MaxParallel:      "1" => "2"
        MinHealthyTime:   "30000000000"
        ProgressDeadline: "600000000000"
      }
      Task: "http"
...

But when changes are made to the scaling block, they're not reported in the diff even though the scheduler correctly identifies an in-place update:

$ nomad job plan httpd.nomad.hcl
+/- Job: "httpd"
+/- Task Group: "web" (1 in-place update)
  Task: "http"

...

This issue was raised internally and the above outputs are from near the HEAD of main. Not sure which versions are impacted but likely to be from whenever we first introduced scaling.

[nvanthao]

Hi @tgross ,

I'm seeing this on at least 3 versions: 1.4.3, 1.5.6 and 1.6.1

Looks like we have no diff implemented for scaling block

nomad/nomad/structs/diff.go

Line 216 in 3e61b3a

func (tg *TaskGroup) Diff(other *TaskGroup, contextual bool) (*TaskGroupDiff, error) {

I would like to work on this bug. Please let me know if you have any concern.

[lgfa29]

Hi @nvanthao 👋

Thank you for the interest! I don't think there's any specific concerns here, and your assessment seems correct. Feel free to work on a PR to fix this and let us know if you need any help 🙂

[nvanthao]

Thanks @lgfa29 I'm working on this now and will update us with the PR later.