# RDS RI Coverage Below 50%

> ZopNight flags an RDS instance with no reservation on file only after 60+ days of history, high uptime and real utilization prove it a commitment candidate, then prices a 1-year RI at 730 hours against the compute-only line. Storage, IOPS and backups are excluded because an RI never discounts them.

Source: https://zop.dev/integrations/aws/recommendations/rds-ri-coverage-below-50
Updated: 2026-08-19

---

## Coverage comes from billing data, not a tag

The authoritative signal is the reservation-coverage map derived from the AWS Cost and
Usage Report. A database whose usage already carries a Reservation or Savings Plan
label is covered, so the rule abstains rather than recommend re-buying. A database with
no label has no commitment at all: 0% coverage, exactly the below-50% gap this rule
exists to close. When an `ri_coverage_pct` tag is present it refines the displayed
percentage (and a tagged value of 50 or above suppresses the finding), but the tag
never decides firing. An earlier version gated on that tag alone, and since nothing
ever produced it, the rule was permanently dead.

## An RI only discounts compute

An RDS Reserved Instance discounts the instance-hour line and nothing else. Storage,
provisioned IOPS and backups [go on billing at list price](https://aws.amazon.com/rds/pricing/) regardless. Feeding the full
monthly bill into the break-even would credit the RI with money it never touches: on a
500 GB instance the overstatement approaches 77%. So the break-even basis is capped at
the on-demand compute rate times 730 hours whenever that catalog rate is known, and the
RI is recommended only when its fixed monthly price undercuts the compute-only basis.
The saving is the exact net difference, never a flat percentage.

## Proving the database deserves a commitment

A reservation is a 1- or 3-year lock-in, so the rule demands evidence first: at least
60 days of observed history, high uptime, and meaningful utilization. A part-time
database gets uptime-suppressed, because buying 730 hours a month for an instance that runs
office hours wastes most of the commitment. An underutilized one should be rightsized
before anything is locked in.

## When nothing is reported

Each of these abstains: existing Reservation or Savings Plan coverage, a coverage tag
at or above 50%, a missing or zero monthly cost, a failed eligibility bar, measured
uptime below the commitment floor, or missing live RI rates. The rule never
falls back to a published average discount when the real rates are absent.

## Audit your coverage in one call

```bash
aws ce get-reservation-coverage \
  --time-period Start=$(date -u -v-30d +%Y-%m-%d),End=$(date -u +%Y-%m-%d) \
  --filter '{"Dimensions":{"Key":"SERVICE","Values":["Amazon Relational Database Service"]}}'
```

A `CoverageHoursPercentage` under 50 across a stable fleet is this rule's territory.
Before purchasing, match the RI to the engine and instance class, weigh 1-year against
3-year terms, and check Multi-AZ alignment. A reservation that does not match what
actually runs discounts nothing.