Kubernetes v1.36: New Metric for Route Sync in the Cloud Controller Manager

By Lukas Metzner (Hetzner) |

Kubernetes v1.36 introduces a new alpha counter metric route_controller_route_sync_total to the Cloud Controller Manager (CCM) route controller implementation at k8s.io/cloud-provider. This metric increments each time routes are synced with the cloud provider.

A/B testing watch-based route reconciliation

This metric was added to help operators validate the CloudControllerManagerWatchBasedRoutesReconciliation feature gate introduced in Kubernetes v1.35. That feature gate switches the route controller from a fixed-interval loop to a watch-based approach that only reconciles when nodes actually change. This reduces unnecessary API calls to the infrastructure provider, lowering pressure on rate-limited APIs and allowing operators to make more efficient use of their available quota.

To A/B test this, compare route_controller_route_sync_total with the feature gate disabled (default) versus enabled. In clusters where node changes are infrequent, you should see a significant drop in the sync rate with the feature gate turned on.

Example: expected behavior

With the feature gate disabled (the default fixed-interval loop), the counter increments steadily regardless of whether any node changes occurred:

# After 10 minutes with no node changes
route_controller_route_sync_total 60
# After 20 minutes, still no node changes
route_controller_route_sync_total 120

With the feature gate enabled (watch-based reconciliation), the counter only increments when nodes are actually added, removed, or updated:

# After 10 minutes with no node changes
route_controller_route_sync_total 1
# After 20 minutes, still no node changes — counter unchanged
route_controller_route_sync_total 1
# A new node joins the cluster — counter increments
route_controller_route_sync_total 2

The difference is especially visible in stable clusters where nodes rarely change.

Where can I give feedback?

If you have feedback, feel free to reach out through any of the following channels:

How can I learn more?

For more details, refer to KEP-5237.