cloudwatch: `MetricFilter.metric()` does not use dimensions

[jakajancar]

Describe the bug

The Metric returned from MetricFilter.metric() uses the namespace and name from the filter, but not the dimensions.

Not really a problem since you can override the dimensions manually, either by passing them when calling MetricFilter.metric() or by just creating the metric from scratch, but it seems reasonable to expect all of the filter properties would be passed to the metric.

Regression Issue

• Select this option if this issue appears to be a regression.

Last Known Working CDK Library Version

No response

Expected Behavior

x

Current Behavior

x

Reproduction Steps

x

Possible Solution

No response

Additional Information/Context

No response

AWS CDK Library version (aws-cdk-lib)

v22.14.0

AWS CDK CLI version

2.1018.0

Node.js Version

v22.14.0

OS

linux

Language

TypeScript

Language Version

No response

Other information

No response

[jakajancar]

Specifically here:

  @MethodMetadata()
  public metric(props?: MetricOptions): Metric {
    return new Metric({
      metricName: this.metricName,
      namespace: this.metricNamespace,
      dimensionsMap: this.dimensions, <-- should be added
      statistic: 'avg',
      ...props,
    }).attachTo(this);

And probably also unit.

[ykethan]

Hey @jakajancar, thank you for reaching out. I've investigated the issue with MetricFilter.metric() not using dimensions when creating a metric, and can confirm this behavior.

When creating a MetricFilter with dimensions, the dimensions are correctly included in the CloudFormation resource definition. However, when calling metric() on that filter to get a Metric object for use in dashboards or alarms, those dimensions are not transferred to the new metric.

Reproduction

I created a simple CDK app to reproduce this issue:

const logGroup = new logs.LogGroup(this, 'LogGroup');

// Create a metric filter with dimensions
const filter = new logs.MetricFilter(this, 'MetricFilter', {
  logGroup,
  filterPattern: logs.FilterPattern.literal('ERROR'),
  metricNamespace: 'MyApp',
  metricName: 'ErrorCount',
  dimensions: { Service: 'API' },
  unit: cw.Unit.COUNT,
});

// Without explicitly passing dimensions (demonstrates the bug)
const buggyMetric = filter.metric();

// With explicit dimensions (workaround)
const fixedMetric = filter.metric({
  dimensionsMap: { Service: 'API' },
  unit: cw.Unit.COUNT,
});

// Create a dashboard to compare the metrics
new cw.Dashboard(this, 'Dashboard', {
  dashboardName: 'MetricFilterDimensionsTest',
  widgets: [
    [
      new cw.GraphWidget({
        title: 'Without dimensions (bug)',
        left: [buggyMetric],
      }),
      new cw.GraphWidget({
        title: 'With dimensions (workaround)',
        left: [fixedMetric],
      }),
    ],
  ],
});

In the synthesized CloudFormation template, the MetricFilter correctly includes dimensions:

MetricFilter1B93B6E5:
  Type: AWS::Logs::MetricFilter
  Properties:
    FilterPattern: ERROR
    LogGroupName:
      Ref: LogGroupF5B46931
    MetricTransformations:
      - Dimensions:
          - Key: Service
            Value: API
        MetricName: ErrorCount
        MetricNamespace: MyApp
        MetricValue: "1"
        Unit: Count

But in the dashboard metrics section:

"metrics":[["MyApp","ErrorCount"]]  // Without dimensions 
"metrics":[["MyApp","ErrorCount","Service","API"]]  // With dimensions 

This confirms that when using filter.metric() without manually providing the dimensions, the resulting metric doesn't include the dimensions that were already defined in the filter.

Technical Details

As you have correctly pointed, the issue appears to be in:

• File: packages/aws-cdk-lib/aws-logs/lib/metric-filter.ts
• Method: metric()
  Current implementation:

@MethodMetadata()
public metric(props?: MetricOptions): Metric {
  return new Metric({
    metricName: this.metricName,
    namespace: this.metricNamespace,
    statistic: 'avg',
    ...props,
  }).attachTo(this);
}

The method doesn't pass the dimensions from the filter to the new Metric object. The same also applies to the unit property.

Workaround

Until this is fixed, you can work around the issue by explicitly providing the dimensions when calling metric():

// Get dimensions from the filter
const metric = filter.metric({
  dimensionsMap:  { Service: 'API' }
});

Fix

The issue can be fixed by modifying the metric() method to include the dimensions and unit:

@MethodMetadata()
public metric(props?: MetricOptions): Metric {
  return new Metric({
    metricName: this.metricName,
    namespace: this.metricNamespace,
    dimensionsMap: this.dimensions,  // Add dimensions from the filter
    unit: this.unit,                 // Add unit from the filter
    statistic: 'avg',
    ...props,
  }).attachTo(this);
}

This change ensures that dimensions and unit configured on the MetricFilter are properly passed to the created Metric. Note that if props includes dimensionsMap or unit, those values will still override the ones from the filter.

References

• MetricFilter class in aws-cdk
• AWS CloudFormation MetricFilter documentation

Marking as P2. We greatly appreciate community contributions! If you are interested in implementing this on a Pull Request. Please review the contribution guidelines. Meanwhile, welcome to add 👍 to this issue to help us prioritize.

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