CloudWatch Metric Guide
EvictionsAmazon ElastiCache CloudWatch metric
Evictions counts the number of keys removed from the cache because the node hit its maxmemory limit — the engine had to make room for new writes by forcibly discarding existing data (distinct from keys expiring naturally via TTL).
What it measures
About Evictions
Evictions counts the number of keys removed from the cache because the node hit its maxmemory limit — the engine had to make room for new writes by forcibly discarding existing data (distinct from keys expiring naturally via TTL).
| Namespace | AWS/ElastiCache |
| Metric name | Evictions |
| Unit | Count |
| AWS docs | Official Amazon ElastiCache metrics reference |
Why this metric matters
Evictions is one of the earliest and clearest warning signs available on ElastiCache, because it means the engine ran out of room and started throwing away data you didn't ask it to expire. For a workload using the cache as a pure, disposable acceleration layer (session cache, hot-path lookups with a DB fallback), occasional low-level eviction may be tolerable — but a sustained climb means cache hit rate is degrading in real time, and every eviction is a request that will now fall through to the origin database instead, adding load exactly where you can least afford it.
Evictions and DatabaseMemoryUsagePercentage move together but tell you different things: memory percentage tells you how close you are to the edge, Evictions tells you the edge has already been crossed and data loss is actively happening. A cluster can sit at 99% DatabaseMemoryUsagePercentage indefinitely with zero evictions if the working set is static — it's the combination of high memory usage plus rising Evictions that signals real trouble.
Recommended alarm threshold for Evictions
Recommended threshold
> 0, sustained for 5 minutes
AWS's own documentation explicitly declines to publish a fixed threshold here — "we recommend that you determine your own alarm threshold for this metric based on your application needs." The > 0 sustained-for-5-minutes floor is a Nuberio recommendation: for most workloads any non-trivial, ongoing eviction rate is worth a page, since it directly predicts falling cache hit rate and rising origin-database load. Teams intentionally running a cache at capacity as a pure LRU layer should raise this threshold to match their tolerated miss rate instead of alarming on any eviction.
Is your Evictions alarm already set up correctly?
The free Nuberio Audit scans your CloudWatch setup and flags missing or misconfigured alarms — including Evictions — in 5 minutes.
Common failures that show up in Evictions
When Evictions reaches an alarm threshold, these are the most common root causes — in order of how often Nuberio sees them across customer AWS accounts.
Dataset growth outpacing the node's memory capacity as the application adds more cached keys over time
maxmemory-policy misconfiguration (e.g. noeviction on a cache-only workload) causing writes to fail instead of evicting — or an eviction policy that evicts the wrong keys for the access pattern
A small number of very large values (big hashes, lists, or cached blobs) consuming disproportionate memory and crowding out the rest of the working set
Missing or absent TTLs on keys that should expire, so memory pressure builds from data that was never meant to be long-lived
Node type downsizing or a failed scale-up leaving the cluster under-provisioned for its actual working set
How the Nuberio Audit checks Evictions
The free Audit scans every Amazon ElastiCache resource in your account and checks whether a Evictions alarm exists, whether its threshold and evaluation period are configured sensibly, and flags it if it's missing entirely. Every finding comes with the exact CLI command to fix it — read-only access, no credit card, results in about 5 minutes.
Nuberio Audit
Scans your CloudWatch setup for missing or misconfigured Evictions alarms. Free, 5-minute read-only scan.
Related Amazon ElastiCache metrics
Evictions rarely fails in isolation. These metrics tend to correlate — monitor them together for complete Amazon ElastiCache coverage.
FAQ
Frequently asked questions about Evictions
Common questions about setting up CloudWatch alarms for Evictions in Amazon ElastiCache.
What is the recommended CloudWatch alarm threshold for Evictions?+
> 0, sustained for 5 minutes. AWS's own documentation explicitly declines to publish a fixed threshold here — "we recommend that you determine your own alarm threshold for this metric based on your application needs." The > 0 sustained-for-5-minutes floor is a Nuberio recommendation: for most workloads any non-trivial, ongoing eviction rate is worth a page, since it directly predicts falling cache hit rate and rising origin-database load. Teams intentionally running a cache at capacity as a pure LRU layer should raise this threshold to match their tolerated miss rate instead of alarming on any eviction.
Which CloudWatch namespace does Evictions belong to?+
Evictions is published in the AWS/ElastiCache namespace with a unit of Count. You can find it in the CloudWatch console under "Metrics" → "AWS/ElastiCache". See the Amazon ElastiCache CloudWatch metrics reference in the AWS documentation.
Does Nuberio automatically create CloudWatch alarms for Evictions?+
No — the free Nuberio Audit does not create alarms for you. It scans your CloudWatch setup and tells you which Amazon ElastiCache resources are missing a Evictions alarm, then gives you the exact CLI command to create it yourself.
Can I use Nuberio without already having a Evictions alarm set up?+
Yes. The free Audit works whether or not you have any Evictions alarm configured — it reads the resource directly from CloudWatch and tells you which resources need one, plus the copy-paste AWS CLI command to create it.
This page is part of the CloudWatch metric guide — thresholds and debugging guidance for every metric across RDS, Lambda, ECS, ALB, EC2, and DynamoDB. To find which Amazon ElastiCache alarms your account is missing — including Evictions — run the free CloudWatch alarm audit. The scan takes under 5 minutes and requires no account.