Premium Azure Cache for Redis instances in production with no reservation

Which Redis tiers can be reserved at all

Azure Cache for Redis reservations prepay compute for one or three years in exchange for a discount. Microsoft’s support table is short: Basic and Standard, no; Premium, yes; Enterprise and Enterprise Flash, yes. Reservations are sold per node, and a Premium cache has two nodes by default, so one cache takes two reservation units. The discount does not cover networking or storage.

Existing and new caches pick up the reservation automatically up to the reserved size, so there is no migration step. The same page also carries Microsoft’s notice that Azure Cache for Redis has announced a retirement timeline for all SKUs, with Azure Managed Redis as the destination. Weigh that before choosing a three-year term.

Finding Premium caches

az redis list \
  --query "[?sku.name=='Premium'].{name:name, rg:resourceGroup, size:sku.capacity, location:location}" \
  -o table

Daily CPU and memory for a candidate over the past month:

az monitor metrics list --resource <cache-resource-id> \
  --metric percentProcessorTime usedmemorypercentage --offset 30d --interval PT24H --aggregation Average

Existing reservations are listed under Reservations in the portal. A cache already covered there is not a candidate.

The checks a cache must pass

1. The name contains prod, production, prd or live, or an environment tag marks it as production.
2. ZopNight has never recorded the cache being stopped.
3. The tier is Premium. Only classic Azure Cache for Redis is in scope, so Premium is the one reservable tier this check sees.
4. No reservation or savings plan covers it and it has no reserved=true tag.
5. At least 60 days of history, uptime of at least 70%, and cache CPU or used memory percentage averaging at least 30%.

Caches that are passed over

Basic and Standard caches, and caches whose tier cannot be read, are skipped rather than sent a recommendation for a reservation they cannot buy. A cache missing any of the utilization or history signals is also skipped. If the break-even comparison below shows the reservation costing more than the cache does today, there is no finding.

Break-even pricing for a cache

ZopNight prefers a break-even figure over a flat discount:

current month   = what the cache is billed now, for the hours it actually ran
reserved month  = 1-year reserved hourly rate x 730
saving          = current month - reserved month   (only when positive)

When those rates are not available it falls back to the current cost multiplied by a discount derived from the rate tiers, and only if uptime is still high enough.

Reserving the cache

1. Confirm the cache stays in service, at this size, for the full term, and check the retirement timeline against a three-year purchase.
2. In the portal, open Reservations, select Add and Azure Cache for Redis.
3. Pick the region, the Premium tier size and the term, and buy one unit per node.
4. Recheck the cache’s cost after the next billing day to confirm the reservation applied.