Bug: addDimensions() is one dimension more restrictive than addDimension() at the boundary

[svozza]

Expected Behavior

addDimension() and addDimensions() should enforce the same maximum dimension limit. When there are 28 dimensions and a user adds 1 more, both methods should either allow or reject it consistently.

Current Behavior

addDimension() uses <= (Metrics.ts:250):

if (MAX_DIMENSION_COUNT <= this.#dimensionsStore.getDimensionCount()) {

addDimensions() uses >= (Metrics.ts:285):

if (currentCount + newSetCount >= MAX_DIMENSION_COUNT) {

At the boundary (28 existing dimensions, adding 1 more to reach the MAX_DIMENSION_COUNT of 29), addDimension() allows it but addDimensions() throws a RangeError.

Code snippet

import { Metrics, MetricUnit } from '@aws-lambda-powertools/metrics';

const metricsA = new Metrics({ namespace: 'test' });
const metricsB = new Metrics({ namespace: 'test' });

// Fill both to 28 dimensions (1 default "service" + 27 regular)
for (let i = 1; i < 28; i++) {
  metricsA.addDimension(`dimension-${i}`, 'test');
  metricsB.addDimension(`dimension-${i}`, 'test');
}

// ✅ addDimension allows the 29th dimension
metricsA.addDimension('final', 'test');

// ❌ addDimensions rejects the 29th dimension
metricsB.addDimensions({ final: 'test' });
// RangeError: The number of metric dimensions must be lower than 29

Steps to Reproduce

1. Create a Metrics instance (which auto-adds service as a default dimension)
2. Add 27 dimensions via addDimension() to reach 28 total
3. Call addDimensions({ final: 'test' }) to add the 29th
4. Observe RangeError — while addDimension('final', 'test') would have succeeded

Possible Solution

Ensure both addDimension() and addDimensions() allow 29 dimensions.

Powertools for AWS Lambda (TypeScript) version

2.33.0

AWS Lambda function runtime

22.x

Packaging format used

npm

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[dreamorosi]

Wow that's not great - how did you find this? Good catch!

[vishwakt]

@dreamorosi can i pick this one up?