CloudWatch

Overview

CloudMock emulates Amazon CloudWatch metrics and alarms, supporting metric data ingestion, querying, alarm creation with manual state management, and tagging.

Supported Operations

Operation	Status	Notes
PutMetricData	Supported	Stores metric data points
GetMetricData	Supported	Retrieves metric data with a metric query
ListMetrics	Supported	Returns all metrics with optional namespace/name filter
PutMetricAlarm	Supported	Creates or updates an alarm
DescribeAlarms	Supported	Returns alarms with optional name/state filter
DeleteAlarms	Supported	Removes one or more alarms
SetAlarmState	Supported	Manually sets an alarm state (OK, ALARM, INSUFFICIENT_DATA)
DescribeAlarmsForMetric	Supported	Returns alarms linked to a specific metric
TagResource	Supported	Adds tags to an alarm
UntagResource	Supported	Removes tags from an alarm
ListTagsForResource	Supported	Returns tags for an alarm

Quick Start

curl

# Put metric data
curl -X POST "http://localhost:4566/?Action=PutMetricData&Namespace=MyApp&MetricData.member.1.MetricName=RequestCount&MetricData.member.1.Value=42&MetricData.member.1.Unit=Count"

# List metrics
curl -X POST "http://localhost:4566/?Action=ListMetrics&Namespace=MyApp"

Node.js

import { CloudWatchClient, PutMetricDataCommand, PutMetricAlarmCommand } from '@aws-sdk/client-cloudwatch';

const cw = new CloudWatchClient({
  endpoint: 'http://localhost:4566',
  region: 'us-east-1',
  credentials: { accessKeyId: 'test', secretAccessKey: 'test' },
});

await cw.send(new PutMetricDataCommand({
  Namespace: 'MyService',
  MetricData: [
    { MetricName: 'Errors', Value: 5, Unit: 'Count' },
    { MetricName: 'Latency', Value: 120, Unit: 'Milliseconds' },
  ],
}));

await cw.send(new PutMetricAlarmCommand({
  AlarmName: 'HighErrorRate', MetricName: 'Errors', Namespace: 'MyService',
  Statistic: 'Sum', Period: 60, EvaluationPeriods: 1,
  Threshold: 10, ComparisonOperator: 'GreaterThanOrEqualToThreshold',
}));

Python

import boto3

cw = boto3.client('cloudwatch', endpoint_url='http://localhost:4566',
                  aws_access_key_id='test', aws_secret_access_key='test',
                  region_name='us-east-1')

cw.put_metric_data(
    Namespace='MyService',
    MetricData=[
        {'MetricName': 'Errors', 'Value': 5, 'Unit': 'Count'},
        {'MetricName': 'Latency', 'Value': 120, 'Unit': 'Milliseconds'},
    ],
)

cw.put_metric_alarm(
    AlarmName='HighErrorRate', MetricName='Errors', Namespace='MyService',
    Statistic='Sum', Period=60, EvaluationPeriods=1,
    Threshold=10, ComparisonOperator='GreaterThanOrEqualToThreshold',
)

# Manually trigger alarm for testing
cw.set_alarm_state(AlarmName='HighErrorRate', StateValue='ALARM', StateReason='Test')

Configuration

cloudmock.yml

services:
  cloudwatch:
    enabled: true

No additional service-specific configuration is required.

Known Differences from AWS

• Metric data is stored in memory and queryable for the duration of the process.
• Alarm state transitions do not trigger SNS notifications or Auto Scaling actions.
• GetMetricData supports standard statistics (Sum, Average, Min, Max, SampleCount).
• Composite alarms are not implemented.
• Metric math expressions are not supported.
• Dashboards are not implemented.

Error Codes

Code	HTTP Status	Description
ResourceNotFound	404	The specified alarm does not exist
InvalidParameterValue	400	An input parameter is invalid
LimitExceededFault	400	The request exceeds a service limit
InvalidParameterCombination	400	Parameters cannot be used together