docs: document Spock 6 preview support

[tsivaprasad]

Summary

This PR documents the preview support for Spock 6, native replication slot failover behavior, and the corresponding changelog entries.

Changes

• Add a "Spock 6 Preview Images" section to docs/using/image-management.md
  explaining how to use the Spock 6 preview manifest entry ("stability": "dev"), either by setting postgres_version/spock_version directly
  or by pinning orchestrator_opts.swarm.image, and its exclusion from
  the image-upgrade action and available_upgrades.
• Add a note to docs/prerequisites/concepts.md's Instances section
  describing automatic native replication slot failover
  (sync_replication_slots/synchronized_standby_slots) for databases
  running Spock 6 on Postgres 17+.
• Add a changelog entry for Spock 6 foundational support.

Testing

• Docs-only change; no code paths touched.

Verification:

curl -X POST http://localhost:3000/v1/databases \
        -H 'Content-Type:application/json' \
        --data '{
            "id": "example",
            "spec": {
                "database_name": "example",
                "database_users": [
                    {
                        "username": "admin",
                        "db_owner": true,
                        "attributes": ["SUPERUSER", "LOGIN"]
                    }
                ],
                "postgres_version": "18.6",
                "spock_version": "6",
                "orchestrator_opts": {
                    "swarm": {
                        "image": "ghcr.io/pgedge/pgedge-postgres:18-spock6-standard"
                    }
                },
                "nodes": [
                    { "name": "n1", "host_ids": ["host-1"] },
                    { "name": "n2", "host_ids": ["host-2"] }
                ]
            }
        }'

cp1-req list-databases
HTTP/1.1 200 OK
Content-Length: 943
Content-Type: application/json
Date: Wed, 02 Sep 2026 05:36:29 GMT

{
  databases: [
    {
      created_at: "2026-09-02T05:35:14Z"
      id: "example"
      instances: [
        {
          created_at: "2026-09-02T05:35:17Z"
          host_id: "host-1"
          id: "example-n1-689qacsi"
          node_name: "n1"
          postgres: {
            patroni_state: "running"
            role: "primary"
            version: "18.6"
          }
          spock: {
            read_only: "off"
            subscriptions: [
              {
                name: "sub_n2_n1"
                provider_node: "n2"
                status: "replicating"
              }
            ]
            version: "6.0.0"
          }
          state: "available"
          status_updated_at: "2026-09-02T05:36:26Z"
          updated_at: "2026-09-02T05:35:50Z"
        }
        {
          created_at: "2026-09-02T05:35:17Z"
          host_id: "host-2"
          id: "example-n2-9ptayhma"
          node_name: "n2"
          postgres: {
            patroni_state: "running"
            role: "primary"
            version: "18.6"
          }
          spock: {
            read_only: "off"
            subscriptions: [
              {
                name: "sub_n1_n2"
                provider_node: "n1"
                status: "replicating"
              }
            ]
            version: "6.0.0"
          }
          state: "available"
          status_updated_at: "2026-09-02T05:36:26Z"
          updated_at: "2026-09-02T05:35:50Z"
        }
      ]
      state: "available"
      updated_at: "2026-09-02T05:35:14Z"
    }
  ]
}

Checklist

• Documentation updated (if needed)

PLAT-734

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---

📝 Walkthrough

Walkthrough

The changelog and documentation add foundational Spock 6 preview support for Docker Swarm, document manifest-based image selection and upgrade restrictions, and clarify automatic native replication slot failover on eligible PostgreSQL nodes.

Changes

Spock 6 support

Layer / File(s)	Summary
Spock 6 preview images docs/using/image-management.md	Documents Docker Swarm-only preview images, the manifest’s PostgreSQL 18.6 pairing, database creation requirements, unsupported Spock 5.x upgrades, and preview-image restrictions.
Native replication slot failover changes/unreleased/Added-20260827-140429.yaml, docs/prerequisites/concepts.md	Adds the Spock 6 preview changelog entry and documents automatic sync_replication_slots configuration, with synchronized_standby_slots configured when read replicas exist.

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The patch grows clear beneath the moon,
Small changes hop in place,
Tests guard the garden path,
Reviews bloom before the dawn.

Merge Risk: 🔵 Low · up to 6b34d

The preview documentation may become stale because its support and manifest statements use time-relative wording. This is a bounded documentation accuracy risk and does not affect runtime behavior.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly identifies the main change: documenting Spock 6 preview support. It follows the repository's Conventional Commits format.
Description check	✅ Passed	The description includes a summary, high-level changes, testing details, verification output, a linked issue, and a documentation checklist item. It does not explicitly complete the remaining checklis…
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0…
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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The description includes a summary, high-level changes, testing details, verification output, a linked issue, and a documentation checklist item. It does not explicitly complete the remaining checklist items or provide reviewer notes, but it is sufficiently complete for this documentation-only change.

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Explanation

No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check. Docstring coverage is scoped to functions touched by this diff. Analyzed 0 functions across 0 files. (3 skipped: 3 unsupported.)

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Inline comments:
In `@docs/prerequisites/concepts.md`:
- Around line 40-41: Update the documentation statement to cover Spock 6 or
later on Postgres 17 or later, and qualify that the Control Plane configures the
native replication slot failover setting only when peer instance IDs produce a
non-empty synchronized standby slot list, matching NeedsNativeFailoverSlots and
DefaultGUCs.

Apply the same fix in `@docs/prerequisites/concepts.md` around lines 42 - 43.

In `@docs/using/image-management.md`:
- Around line 269-270: Update the Spock 6 preview availability statement to
remove the relative word “today”; use the timeless phrasing that it is available
as a preview manifest entry, while preserving the existing stability and
Postgres 18.6 details.

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• changes/unreleased/Fixed-20260821-141322.yaml
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[jason-lynch]

I have a few questions:

• Is this preview support only for Docker Swarm, or should we also support systemd?
  • Right now, the systemd orchestrator filters out Spock 6 packages.
  • If we do want to support systemd, we should also make sure the documentation is clear that this preview does not support upgrading an existing database to Spock 6. You have a note about it in the context of images, but our validation is on the spock_version field, not just the image.
• Should we be using the mutable image tag in the manifest?
  • Our update workflow depends on diffs between the current and desired state, so I'm worried that might make it difficult for users to update their database.
  • We could just use the normal immutable tags and then keep the manifest.json up-to-date as new images are built and tested.
• Should we also add the Postgres 16 and 17 + Spock 6 images to our manifest?
  • We currently only have one for Postgres 18.6

[tsivaprasad]

I have a few questions:

• Is this preview support only for Docker Swarm, or should we also support systemd?

  • Right now, the systemd orchestrator filters out Spock 6 packages.
  • If we do want to support systemd, we should also make sure the documentation is clear that this preview does not support upgrading an existing database to Spock 6. You have a note about it in the context of images, but our validation is on the spock_version field, not just the image.

• Should we be using the mutable image tag in the manifest?

  • Our update workflow depends on diffs between the current and desired state, so I'm worried that might make it difficult for users to update their database.
  • We could just use the normal immutable tags and then keep the manifest.json up-to-date as new images are built and tested.

• Should we also add the Postgres 16 and 17 + Spock 6 images to our manifest?

  • We currently only have one for Postgres 18.6

Thanks for the review. I checked each of these points:

• Docker Swarm vs. systemd: This preview is currently Docker Swarm only. The systemd orchestrator has supportedSpockVersions hardcoded to ["50"], so it cannot discover or use Spock 6 packages today. I’ve updated the documentation to make the Docker Swarm-only scope explicit.

• Existing database upgrades: I’ve also clarified that Spock 6 preview support is create-only. There is currently no supported upgrade path from an existing Spock 5.x database to Spock 6. One additional detail I found is that ValidateChangedSpec does not actually prevent changing spock_version on an existing database; it only validates changes to the PostgreSQL major version. So a spock_version bump is currently unsupported/unsafe rather than explicitly blocked by validation.

• Mutable vs. immutable image tags: I agree this should be considered together with the update workflow. Since updates depend on detecting differences between the current and desired state, immutable tags are likely safer and make image changes explicit. Rather than changing the tagging strategy as part of this documentation PR, I suggest settling this when we update the manifest with the additional Spock 6 images.

• Postgres 16/17 + Spock 6: I checked the upstream registry, and Spock 6 images for PostgreSQL 16 and 17 already exist. So this is not an image-build availability gap; they are simply not present in our manifest yet. I suggest validating PostgreSQL 16/17 + Spock 6 support and adding those entries to manifest.json in a separate PR. We can resolve the mutable-vs.-immutable tag question there as well, and I’ll follow up with the corresponding documentation update once that lands.

For now, I’ll keep this PR scoped to documenting the existing PostgreSQL 18.6 + Spock 6 Docker Swarm preview.
What do you think?

[jason-lynch]

Docker Swarm vs. systemd: This preview is currently Docker Swarm only. The systemd orchestrator has supportedSpockVersions hardcoded to ["50"], so it cannot discover or use Spock 6 packages today. I’ve updated the documentation to make the Docker Swarm-only scope explicit.

Thanks for making this change!

Existing database upgrades: I’ve also clarified that Spock 6 preview support is create-only. There is currently no supported upgrade path from an existing Spock 5.x database to Spock 6. One additional detail I found is that ValidateChangedSpec does not actually prevent changing spock_version on an existing database; it only validates changes to the PostgreSQL major version. So a spock_version bump is currently unsupported/unsafe rather than explicitly blocked by validation.

Thank you for pointing this out! I remembered reviewing this change from Moiz, but I forgot that we didn't merge it. This is a blocker for the release. Our validation should disallow changes to the Spock major version for existing nodes and databases. Could you please fix this either in this PR or another one?

• Mutable vs. immutable image tags: I agree this should be considered together with the update workflow. Since updates depend on detecting differences between the current and desired state, immutable tags are likely safer and make image changes explicit. Rather than changing the tagging strategy as part of this documentation PR, I suggest settling this when we update the manifest with the additional Spock 6 images.
• Postgres 16/17 + Spock 6: I checked the upstream registry, and Spock 6 images for PostgreSQL 16 and 17 already exist. So this is not an image-build availability gap; they are simply not present in our manifest yet. I suggest validating PostgreSQL 16/17 + Spock 6 support and adding those entries to manifest.json in a separate PR. We can resolve the mutable-vs.-immutable tag question there as well, and I’ll follow up with the corresponding documentation update once that lands.

For now, I’ll keep this PR scoped to documenting the existing PostgreSQL 18.6 + Spock 6 Docker Swarm preview.
What do you think?

I'm fine with limiting the preview to 18.6 and Spock 6, but I think the mutable tags are a blocker for this release. I'm raising it now because it will change some of the wording that you're adding in this PR, but if you'd rather edit it again in another PR, then that's OK with me.