Cloud cost
Observability tax
The cost of the monitoring stack itself (hosts, custom metrics, traces, and logs) growing on its own, independent of the infrastructure it's watching.
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Definition
Every other line on a cloud bill scales with a decision someone made on purpose: more instances, more storage, more traffic. Observability spend scales with side effects of normal operation instead: a tag a developer added, a debug log statement left in, an autoscale spike. Nobody provisions an observability bill increase the way they provision a new instance, which is exactly why it tends to go unwatched by the same team that diligently reviews the infrastructure it's monitoring.
The fix isn't monitoring less. It's treating the monitoring bill as its own reviewable line item, with its own metrics (cardinality, host peaks, indexed log volume) instead of assuming it moves in lockstep with the infrastructure underneath it.
Where it shows up
Observability tax appears as its own line item on a monitoring vendor's invoice, separate from the infrastructure spend it watches, tracked through metrics like host count, custom metric cardinality, trace volume, and indexed log volume, all visible in that vendor's own usage dashboard alongside the invoice total.
What makes it expensive
This gets expensive fast: assuming the monitoring bill tracks the infrastructure bill automatically, when a tag a developer added or a debug log left in production can move it independently. The monitoring invoice needs a review slot of its own, on the same cadence as the infrastructure it watches, because nothing about the two moves together.
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The invoice is a lagging signal.
A monthly invoice tells you what already happened. CostMon builds a daily baseline, so a spike stands out while you can still act on it.