Track CCM route syncs against cloud API quotas
route_controller_route_sync_total is an alpha counter in Kubernetes v1.36. It increments each time the route controller synchronises routes with the cloud provider, so it gives a direct count of reconciliation activity rather than a vague sense that “things look busy”.
That matters because route syncs are not free. In a fixed-interval loop, the controller keeps calling out even when the node set is stable. If the cloud provider API is rate-limited, the wasted calls still count against quota.
Why the route sync counter is the signal to watch
The metric is useful because it measures behaviour at the controller boundary. One sync means one round of route reconciliation work, and that is the part that hits provider APIs.
Fixed-interval reconciliation burns quota even when nothing changes
With the feature gate disabled, the route controller keeps running on a fixed interval. If the cluster has no node changes for ten minutes, the counter still climbs. Leave it alone for another ten minutes and it climbs again. Nothing has changed in the cluster, yet the controller has still spent API calls.
That is the waste to watch. It shows up as a steady background rate rather than spikes tied to actual node events. If the provider has tight quotas, that background rate becomes the problem long before anyone notices degraded routing.
Watch-based reconciliation should flatten the counter between node events
With CloudControllerManagerWatchBasedRoutesReconciliation enabled, the route controller switches to watch-based reconciliation. Syncs should then happen when nodes are added, removed, or updated. Between those events, the counter should sit flat.
That gives you a clean contrast. A stable cluster should produce a mostly flat line. A node churn event should produce a visible step. If the counter keeps rising without matching node activity, the watch-based path is not behaving as expected, or the feature gate is not actually active.
Reading the metric against provider quota pressure
The value of the counter is not the absolute number on its own. It is the rate, and how that rate compares with cluster churn and quota headroom.
Compare sync rate before and after the feature gate flips
The most useful check is a side-by-side comparison. Run with the feature gate disabled, note the sync count over a fixed window, then repeat with it enabled. The difference should be blunt: the watch-based path should cut routine syncs down to node-driven events.
If the counter barely moves in the enabled case while the cluster is quiet, that is the expected shape. If both runs show similar growth, the controller is still behaving like a timer loop, which defeats the point of the change.
Spot the gap between cluster churn and steady-state API calls
Node churn creates real route work. Steady-state operation should not. The counter should mirror the first and ignore the second.
That gap is where quota pressure shows up. A cluster with regular node updates will still produce syncs, but the total should track those changes rather than a background timer. If the route sync count keeps rising while node events stay flat, the controller is spending quota on empty work.
Using the counter to prove the watch-based path is working
The cleanest test is boring. Leave the cluster alone and watch route_controller_route_sync_total. If the number stays still, the watch-based path is doing its job. Add or update a node and the counter should move once the controller reconciles routes again.
That makes the metric useful for both validation and drift detection. It can show whether CloudControllerManagerWatchBasedRoutesReconciliation is actually reducing calls to the cloud provider API, and it can also catch a controller that has quietly slipped back into old behaviour.
