Writable Layer Size Should Not Be Polled Expensively Every Scrape

Docker storage size is useful, but asking the daemon for deep filesystem inventory on every fast scrape consumed too much monitoring overhead. On hserver the first signal I use for this question is inventory-exporter cached writable-layer metrics. Slow inventory data does not need the same cadence as CPU or packet counters; sampling cost should match how quickly the underlying state changes.

The important part is interpretation rather than collecting another graph. cost-aware telemetry design. That gives the metric a specific operational job instead of making it another number on a dashboard.

The practical control is straightforward: Refresh Docker storage inventory in the background every few minutes, expose cache age, and scrape the cheap cached result more frequently. This also gives me a repeatable check after deployments, exporter changes, or capacity tuning.

Repository evidence for this monitoring behavior is commit 218300b. I keep that reference with the note because a monitoring conclusion is stronger when the configuration and runtime decision that produced it can be inspected later.