Support custom labels on GCE agent VMs

[mikecirioli]

Closes #170

What this does

Adds support for setting custom GCP labels (key-value pairs) on the GCE agent VMs the plugin provisions. This is the plugin equivalent of gcloud compute instances create --labels=[KEY=VALUE,...], and mirrors the existing custom metadata feature.

Labels differ from metadata: a label value is a single word with no spaces (max 63 chars), so the value field is a single-line text box rather than a textarea. Per the existing GCE convention, there is no doCheckXXX form validation - GCP rejects invalid labels at instance-creation time.

How it works

A new CustomLabelItem describable holds each key-value pair. InstanceConfiguration gains an optional customLabels list, exposed in the form UI and via Configuration as Code. The labels are folded into the instance's label map before the system labels are applied, so user labels never clobber the plugin's internal labels, and template-defined labels keep their existing precedence.

CasC example:

customLabels:
  - key: test-label-key
    value: test-label-value
  - key: team
    value: jenkins

UI

$ kubectl exec -n cbci "$pod" -- grep -n -A6 customLabels /var/jenkins_home/core-casc-bundle/jcasc/jenkins.yaml
  116:        customLabels:
  117-          - key: test-label-key
  118-            value: test-label-value
  119-          - key: team
  120-            value: jenkins
  121-        minimumNumberOfInstances: 0
  122-        minimumNumberOfSpareInstances: 1

Testing

• Unit tests for the label fold (custom labels applied, empty keys skipped, system label preserved, null-safe).
• Config round-trip test asserting customLabels persists through the form.
• CasC round-trip test.
• An integration test (ComputeEngineCloudCustomLabelsIT) that provisions a real VM via CasC and asserts the labels land on the instance.

Verified end to end on a live cluster: the configured labels appear on the provisioned GCE VM alongside the plugin's system labels.

🤖 Generated with Claude Code

[mikecirioli]

Need to create a tracking issue and then will take this out of draft

[gbhat618]

Need to create a tracking issue and then will take this out of draft

one exists - #170 😄

need to also update the user visible documentation for this feature usage

[Copilot]

Pull request overview

Adds support for configuring custom GCP instance labels (key/value pairs) on provisioned GCE agent VMs, exposed via both Jenkins UI and Configuration as Code, with test coverage across unit, CasC, and integration layers.

Changes:

• Introduces CustomLabelItem and wires customLabels into InstanceConfiguration and the Jenkins configuration UI.
• Merges configured custom labels into the instance label map during provisioning.
• Adds/extends unit tests, CasC round-trip assertions, and an integration test to verify labels land on real instances.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/main/java/com/google/jenkins/plugins/computeengine/InstanceConfiguration.java	Adds customLabels and folds them into the effective label map during instance creation.
src/main/java/com/google/jenkins/plugins/computeengine/CustomLabelItem.java	New describable for a single label key/value pair.
src/main/resources/com/google/jenkins/plugins/computeengine/InstanceConfiguration/config.jelly	Exposes a repeatable “Custom labels” section in the instance configuration UI.
src/main/resources/com/google/jenkins/plugins/computeengine/CustomLabelItem/config.jelly	UI fragment for editing a label key/value entry.
src/test/java/com/google/jenkins/plugins/computeengine/InstanceConfigurationTest.java	Adds unit tests for label folding behavior (including skipping empty keys and preserving system label).
src/test/java/com/google/jenkins/plugins/computeengine/ConfigAsCodeTest.java	Extends CasC assertions to cover customLabels.
src/test/java/com/google/jenkins/plugins/computeengine/integration/ComputeEngineCloudCustomLabelsIT.java	New integration test that provisions a VM and asserts the instance labels.
src/test/resources/com/google/jenkins/plugins/computeengine/configuration-as-code.yml	Adds example customLabels configuration for CasC tests.
src/test/resources/com/google/jenkins/plugins/computeengine/integration/custom-labels-casc.yml	New CasC bundle used by the integration test.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[gbhat618]

lgtm; a couple of comments about tests.
also need readme updates to mention the new user visible feature

[gbhat618]

PR looks good to me, I have reviewed the new commits. I will allocate some 30min post lunch and if all is good, I will proceed to merge the PR. 🎉

[gbhat618]

Tested, works 🎉 . thank you @mikecirioli