feat(track/2): Smooth cross-track upgrades

[MichaelThamm]

Blocked by:

• feat: Smooth cross-track upgrades #305
• feat: User-defined TF replace_triggered_by grafana-k8s-operator#536
• feat(track/2): User-defined TF replace_triggered_by grafana-k8s-operator#535

Workaround for:

• Failure to remove an oci-resource from a kubernetes based charm juju/juju#21648

Blocks:

• Track the TF spec migration for product modules #201
• Track 2 -> 3 ingress breaks upgrade #280

Relates to:

• "Unable to create integration, got error: no relations found" with the current terraform deployment. #165
• https://github.com/canonical/observability-team/blob/main/notes/discussions/2026-04-23--terraform-tagging.md
• [Documentation] "Cannot upgrade application X: would break relation" juju/terraform-provider-juju#1022
  • howto/manage-charms/#update-a-charm-when-a-relation-would-break
• juju charm data source juju/terraform-provider-juju#1042

Issue

We want a smooth UX for users upgrading across tracks for our product modules: COS and COS Lite. Ideally, a user should be able to take their track/2 state and plan an upgrade to track/3.0 without any manual intervention.

Solution

1. Use the juju_charm datasource to provide the latest revisions for a charm in a specific track.
2. Use lifecycle {replace_triggered_by = [terraform_data.grafana_ingress_interface]} to replace the juju_integration in the event that the interface changes.

Checklist

• PR title makes an appropriate release note and follows conventional commits syntax.
• Merge target is the correct branch, and relevant tandem backport PRs opened.
• Update the README

Context

In the future charms will have unique tracks which the products needs to map to:

• Tagging for TF modules in charm repos observability#427

Testing Instructions

All testing will be conducted in:

• feat: Smooth cross-track upgrades #305

The general idea is to:

1. Deploy COS 2/stable
2. Update TF module source to dev/edge
3. terraform init -upgrade; terraform apply

Documentation

Documentation will be addressed in:

• feat: Cross-track upgrade documentation #174

[MichaelThamm]

Suggested change

	source = "git::https://github.com/canonical/grafana-k8s-operator//terraform?ref=test/lifecycle-input-track-2"
	source = "git::https://github.com/canonical/grafana-k8s-operator//terraform?ref=track/2"

[MichaelThamm]

Make sure to test the full demo again before reverting this and then merge.