CloudWatch: Metrics, Alarms & Dashboards

Amazon CloudWatch is AWS's observability service — metrics, logs, alarms, and dashboards. Almost all AWS services publish metrics to CloudWatch automatically.

Metrics

# List available metrics
aws cloudwatch list-metrics --namespace AWS/EC2 --metric-name CPUUtilization

# Get metric statistics
aws cloudwatch get-metric-statistics   --namespace AWS/EC2   --metric-name CPUUtilization   --dimensions Name=InstanceId,Value=i-1234567890abcdef0   --start-time 2024-03-15T00:00:00Z   --end-time 2024-03-16T00:00:00Z   --period 3600   --statistics Average Maximum

# Common namespaces and metrics:
# AWS/EC2:         CPUUtilization, NetworkIn/Out, DiskReadOps, StatusCheckFailed
# AWS/RDS:         CPUUtilization, DatabaseConnections, FreeStorageSpace, ReadIOPS
# AWS/ALB:         RequestCount, TargetResponseTime, HTTPCode_Target_5XX_Count
# AWS/Lambda:      Invocations, Duration, Errors, Throttles, ConcurrentExecutions
# AWS/S3:          NumberOfObjects, BucketSizeBytes (daily)
# AWS/SQS:         NumberOfMessagesSent, ApproximateNumberOfMessagesVisible
# AWS/ECS:         CPUUtilization, MemoryUtilization
# AWS/DynamoDB:    ConsumedReadCapacityUnits, SystemErrors, SuccessfulRequestLatency

Custom Metrics

# Publish custom metric via CLI
aws cloudwatch put-metric-data   --namespace "MyApp"   --metric-name "OrdersProcessed"   --value 42   --unit Count   --dimensions Environment=prod,Service=checkout

# With high-resolution (1-second granularity)
aws cloudwatch put-metric-data   --namespace "MyApp"   --metric-name "ApiLatency"   --value 123.5   --unit Milliseconds   --storage-resolution 1

import boto3

cloudwatch = boto3.client('cloudwatch')

# Publish metric
cloudwatch.put_metric_data(
    Namespace='MyApp',
    MetricData=[
        {
            'MetricName': 'OrdersProcessed',
            'Value': 42,
            'Unit': 'Count',
            'Dimensions': [
                {'Name': 'Environment', 'Value': 'prod'},
                {'Name': 'Service', 'Value': 'checkout'},
            ],
        },
        {
            'MetricName': 'ApiLatency',
            'Value': 123.5,
            'Unit': 'Milliseconds',
            'Dimensions': [{'Name': 'Endpoint', 'Value': '/api/orders'}],
        },
    ]
)

# Batch publish (max 1000 metrics per call)
# Use CloudWatch agent for infrastructure metrics (memory, disk — not built-in)

Alarms

# Create alarm
aws cloudwatch put-metric-alarm   --alarm-name "High-CPU-i-1234567890"   --alarm-description "CPU over 80% for 5 minutes"   --namespace AWS/EC2   --metric-name CPUUtilization   --dimensions Name=InstanceId,Value=i-1234567890abcdef0   --statistic Average   --period 60   --evaluation-periods 5   --threshold 80   --comparison-operator GreaterThanThreshold   --alarm-actions arn:aws:sns:us-east-1:123456789:my-alerts   --ok-actions arn:aws:sns:us-east-1:123456789:my-alerts   --treat-missing-data breaching

# Composite alarm (AND/OR of other alarms)
aws cloudwatch put-composite-alarm   --alarm-name "Service-Down"   --alarm-rule "ALARM("High-CPU") AND ALARM("High-Latency")"

# List alarms
aws cloudwatch describe-alarms --alarm-names "High-CPU-i-1234567890"
aws cloudwatch describe-alarms --state-value ALARM

# Set alarm state (for testing)
aws cloudwatch set-alarm-state   --alarm-name "High-CPU-i-1234567890"   --state-value ALARM   --state-reason "Testing"

# Delete alarm
aws cloudwatch delete-alarms --alarm-names "High-CPU-i-1234567890"

Dashboards

# Create dashboard (JSON body defines widgets)
aws cloudwatch put-dashboard   --dashboard-name "MyApp-Prod"   --dashboard-body file://dashboard.json

# dashboard.json widgets example:
# {
#   "widgets": [
#     {
#       "type": "metric",
#       "properties": {
#         "title": "CPU Utilization",
#         "metrics": [["AWS/EC2", "CPUUtilization", "InstanceId", "i-xxx"]],
#         "period": 300,
#         "stat": "Average",
#         "view": "timeSeries"
#       }
#     },
#     {
#       "type": "alarm",
#       "properties": {
#         "title": "Active Alarms",
#         "alarms": ["arn:aws:cloudwatch:us-east-1:123:alarm:High-CPU"]
#       }
#     }
#   ]
# }

# List dashboards
aws cloudwatch list-dashboards