CloudWatch Metric Guide
Amazon S3 CloudWatch AlarmsThresholds, failures, and debugging guides
4 CloudWatch metrics covered for Amazon S3. Each guide includes the recommended alarm threshold, common root causes, and how Nuberio automatically diagnoses it when it fires.
4
metrics covered
AWS/S3
namespace
5 min
to run a free audit
Amazon S3 metrics
BucketSizeBytes
BucketSizeBytes reports the total size, in bytes, of all objects stored in a bucket for a given storage class — including current and noncurrent object versions, object metadata, and the parts of any incomplete multipart uploads. It is a free, always-on storage metric published once per day.
Threshold
Alarm on a >20% day-over-day increase (or use CloudWatch Anomaly Detection) rather than an absolute byte value
NumberOfObjects
NumberOfObjects reports the total count of objects in a general purpose bucket across all storage classes — including current and noncurrent versions, delete markers, and the parts of incomplete multipart uploads. Like BucketSizeBytes, it is a free storage metric published once per day, filtered with StorageType=AllStorageTypes.
Threshold
Alarm on a >20% day-over-day increase (or use CloudWatch Anomaly Detection) rather than an absolute count
4xxErrors
4xxErrors reports HTTP 4xx client error status codes returned for requests to a bucket, published as 0 or 1 per request. The Sum statistic gives the error count for the period; the Average statistic gives the error rate.
Threshold
Average (error rate) > 5% sustained for 5 minutes — or Sum-based, scaled to your normal request volume
5xxErrors
5xxErrors reports HTTP 5xx server error status codes returned by S3 for requests to a bucket, published as 0 or 1 per request. The Sum statistic gives the error count for the period; the Average statistic gives the error rate.
Threshold
Average (error rate) > 1% sustained for 5 minutes — or Sum > 0 sustained across periods for low-traffic buckets
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Looking for alarms across other AWS services? View the full CloudWatch metric guide — thresholds and debugging guides for RDS, Lambda, ECS, ALB, EC2, and DynamoDB.