Breaking: New Metric Tracks Route Sync in Cloud Controller Manager
Kubernetes v1.36 introduces an 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, giving operators a real-time view of reconciliation activity.
The addition is designed to help operators validate the CloudControllerManagerWatchBasedRoutesReconciliation feature gate, which debuted in Kubernetes v1.35. The metric allows for direct A/B testing between the default fixed-interval reconciliation and the new watch-based approach.
What This Means for Cluster Operators
“By exposing the sync count, we’re giving operators the data they need to prove the watch-based approach reduces API calls in stable clusters,” said a Kubernetes SIG Cloud Provider contributor. “This is a direct path to lowering pressure on rate-limited infrastructure APIs.”
In practice, enabling the feature gate and monitoring the metric can reveal dramatic reductions in sync operations. For example, a cluster with no node changes over 20 minutes will see 120 counter increments under the default loop, but only one under watch-based reconciliation.
Background: From Fixed Intervals to Event-Driven Reconciliation
The CCM route controller traditionally operates on a fixed-interval loop, syncing routes periodically regardless of actual node changes. This wastes API quota and increases pressure on rate-limited cloud provider endpoints.
The CloudControllerManagerWatchBasedRoutesReconciliation feature gate switches this behavior to a watch-based approach that triggers reconciliation only when nodes are added, removed, or updated. The result is far fewer API calls in environments where infrastructure is relatively static.
To A/B test, operators can compare route_controller_route_sync_total with the feature gate disabled (default) versus enabled. The difference is especially visible in stable clusters where node changes are infrequent.
Expected Behavior: Visualizing the Impact
With the feature gate disabled (fixed-interval loop), the counter increments steadily regardless of actual changes:
- After 10 minutes with no node changes:
route_controller_route_sync_total 60 - After 20 minutes, still no changes:
route_controller_route_sync_total 120
With the feature gate enabled (watch-based), the counter only increments on real node events:
- After 10 minutes with no changes:
route_controller_route_sync_total 1 - After 20 minutes, unchanged:
route_controller_route_sync_total 1 - After a new node joins:
route_controller_route_sync_total 2
The metric makes the efficiency gain instantly measurable.
How to Provide Feedback
Feedback on the new metric and feature gate is welcome via these channels:
- The #sig-cloud-provider channel on Kubernetes Slack
- The KEP-5237 issue on GitHub
- The SIG Cloud Provider community page for additional communication options
Learn More
For detailed technical specifications, refer to KEP-5237 in the Kubernetes enhancement tracking repository. The metric is currently alpha and subject to change based on community feedback.
This article was updated to reflect the correct publication date: May 15, 2026.