---
title: Amazon ElastiCache Serverless
description: ElastiCache Serverless removes capacity planning for in-memory caching — automatic scaling, per-second pricing, and zero downtime sizing changes for Redis/Valkey and Memcached.
url: https://www.factualminds.com/glossary/elasticache-serverless/
publishDate: 2026-06-13
updateDate: 2026-06-13
---

# Amazon ElastiCache Serverless

> ElastiCache Serverless removes capacity planning for in-memory caching — automatic scaling, per-second pricing, and zero downtime sizing changes for Redis/Valkey and Memcached.

## Definition

Amazon **ElastiCache Serverless** is a capacity mode for ElastiCache that removes node type selection and cluster resizing. AWS scales **ElastiCache Processing Units (ECPUs)** and memory based on traffic, memory pressure, and configured minimum capacity — billing per second for compute operations and per GB-hour for stored data. Supported engines include **Valkey**, **Redis OSS**, and **Memcached**. Multi-AZ resilience is built in without you managing replica promotion.

Serverless fits **cache** workloads — ephemeral, TTL-driven, reconstructable from a primary database — not durable primary stores. For durable in-memory databases with transaction logs, use **MemoryDB for Valkey**. For DynamoDB-specific microsecond reads, **DAX** remains the specialized path.

## When to use it

- **Bursty or unpredictable** cache traffic — flash sales, viral content, game launches — where provisioned nodes would sit idle or throttle.
- **Dev, staging, and sandbox** environments that should scale to near-zero spend when idle.
- **Multi-tenant SaaS** caches where per-tenant keyspaces have wildly different hit rates.
- Teams without bandwidth to run **Redis sizing spreadsheets** and nightly memory fragmentation drills.

## When not to use it

- Steady **high QPS** 24/7 caches — provisioned clusters with reserved pricing often beat Serverless ECPU meters.
- **Sub-millisecond p99** requirements with custom kernel tuning — provisioned nodes in dedicated VPC layouts win.
- **Primary database** semantics — no durability guarantees; use MemoryDB or Aurora instead.

## Tips

- Set a **minimum ECPU floor** if p99 latency spikes during cold bursts — default scale-from-zero can lag on first traffic after idle.
- Aggressive **TTLs** — you pay GB-hours for every key resident in memory; unbounded session keys are a silent budget leak.
- Compare **30-day side-by-side cost** against a right-sized `cache.r7g` cluster before committing production to Serverless.
- Use **Valkey** engine for new deployments — Linux Foundation fork with active community patches post-Redis SSPL licensing change.
- Monitor **Evictions** and **CurrItems** — rising evictions under flat hit rate means memory ceiling, not "cache working as designed."

## Gotchas

- **Serious:** Choosing Serverless for **steady high-throughput** production without a cost model — ECPU bills exceed provisioned nodes predictably above a utilization threshold.
- **Serious:** Treating Serverless as **durable storage** — evictions and failures expect cache miss + reload; data loss is a design assumption.
- **Regular:** **Large values** (>512 MB strings are wrong architecturally anyway) inflate memory charges and trigger early eviction storms.
- **Regular:** **TLS in-transit** adds CPU — micro-benchmarks in dev without TLS mislead prod latency estimates.
- **Regular:** **Cross-AZ** client-to-cache traffic inside the same region still adds latency — place clients and cache in aligned AZs when possible.

## Official references

- [ElastiCache Serverless limits](https://docs.aws.amazon.com/AmazonElastiCache/latest/dg/serverless.html#serverless-limits) — max data size and throughput ceilings.
- [Choosing between Serverless and node-based](https://docs.aws.amazon.com/AmazonElastiCache/latest/dg/WhatIs.html) — decision factors from AWS.

## Related FactualMinds content

- [MemoryDB for Valkey](/glossary/memorydb-valkey/) — durable in-memory alternative
- [AWS Serverless Architecture](/services/aws-serverless/)
- [AWS Application Modernization](/services/aws-application-modernization/)

## Related AWS Services

- aws-serverless
- aws-application-modernization

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*Source: https://www.factualminds.com/glossary/elasticache-serverless/*