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AWS CloudWatch — Practical Monitoring, Alarms, and Log Collection

Covers how to query CloudWatch metrics, publish custom metrics, configure alarms, query logs with Logs Insights, and build dashboards for EC2, Lambda, and RDS.

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Contents
  1. CloudWatch Core Components
  2. Querying Metrics
  3. Publishing Custom Metrics
  4. Configuring Alarms
  5. CloudWatch Agent (EC2 Memory and Disk)
  6. Logs Insights Queries
  7. Creating a Dashboard

CloudWatch Core Components

ComponentRole
MetricsTime-series numeric data (CPU, memory, etc.)
AlarmsNotifications and actions when a metric exceeds a threshold
LogsCollect log groups and streams
Logs InsightsLog query language
DashboardsVisualize metrics and logs
Events/EventBridgeEvent-driven automation

Querying Metrics

Bash
# EC2 CPU ( 1when, 5 )
aws cloudwatch get-metric-statistics   --namespace AWS/EC2   --metric-name CPUUtilization   --dimensions Name=InstanceId,Value=i-xxxxxxxxxxxxxxxxx   --start-time $(date -u -d '1 hour ago' +%Y-%m-%dT%H:%M:%SZ)   --end-time $(date -u +%Y-%m-%dT%H:%M:%SZ)   --period 300   --statistics Average   --query 'Datapoints[*].[Timestamp,Average]'   --output table

# list
aws cloudwatch list-metrics --namespace AWS/EC2
aws cloudwatch list-metrics --namespace AWS/RDS
aws cloudwatch list-metrics --namespace AWS/Lambda

Publishing Custom Metrics

Bash
# CLI
aws cloudwatch put-metric-data   --namespace "MyApp"   --metric-data '[{
    "MetricName": "ActiveUsers",
    "Value": 150,
    "Unit": "Count",
    "Dimensions": [
      {"Name": "Environment", "Value": "production"}
    ]
  }]'

# Python
import boto3

cw = boto3.client('cloudwatch')
cw.put_metric_data(
    Namespace='MyApp',
    MetricData=[{
        'MetricName': 'OrderCount',
        'Value': 42,
        'Unit': 'Count',
        'Dimensions': [
            {'Name': 'Region', 'Value': 'ap-northeast-2'}
        ]
    }]
)

Configuring Alarms

Bash
# CPU 80% 5 when SNS
aws cloudwatch put-metric-alarm   --alarm-name high-cpu-prod   --alarm-description "CPU over 80%"   --namespace AWS/EC2   --metric-name CPUUtilization   --dimensions Name=InstanceId,Value=i-xxxxxxxxx   --statistic Average   --period 300   --evaluation-periods 2   --threshold 80   --comparison-operator GreaterThanOrEqualToThreshold   --alarm-actions arn:aws:sns:ap-northeast-2:ACCOUNT:alerts   --ok-actions arn:aws:sns:ap-northeast-2:ACCOUNT:alerts

# list
aws cloudwatch describe-alarms   --query 'MetricAlarms[*].[AlarmName,StateValue,MetricName]'   --output table

#
aws cloudwatch set-alarm-state   --alarm-name high-cpu-prod   --state-value ALARM   --state-reason "Testing"

CloudWatch Agent (EC2 Memory and Disk)

EC2's default metrics do not include memory or disk usage, so you need to install the Agent.

Bash
# Agent (Ubuntu)
wget https://s3.amazonaws.com/amazoncloudwatch-agent/ubuntu/amd64/latest/amazon-cloudwatch-agent.deb
sudo dpkg -i amazon-cloudwatch-agent.deb

# settings run
sudo /opt/aws/amazon-cloudwatch-agent/bin/amazon-cloudwatch-agent-config-wizard

# or settings file
sudo tee /opt/aws/amazon-cloudwatch-agent/etc/amazon-cloudwatch-agent.json << 'EOF'
{
  "metrics": {
    "metrics_collected": {
      "mem": {
        "measurement": ["mem_used_percent"],
        "metrics_collection_interval": 60
      },
      "disk": {
        "measurement": ["disk_used_percent"],
        "metrics_collection_interval": 60,
        "resources": ["/", "/data"]
      }
    }
  }
}
EOF

sudo /opt/aws/amazon-cloudwatch-agent/bin/amazon-cloudwatch-agent-ctl   -a fetch-config -m ec2   -c file:/opt/aws/amazon-cloudwatch-agent/etc/amazon-cloudwatch-agent.json -s

Logs Insights Queries

Bash
# CLI run
aws logs start-query   --log-group-name /aws/lambda/my-function   --start-time $(date -d '1 hour ago' +%s)   --end-time $(date +%s)   --query-string 'fields @timestamp, @message | filter @message like /ERROR/ | limit 20'

Queries commonly used in the console:

CODE
# Lambda
fields @timestamp, @message
| filter @message like /ERROR/
| stats count() by bin(5m)

# Lambda run when Top 10
fields @timestamp, @duration
| sort @duration desc
| limit 10

# IP Request (ALB )
fields @timestamp, clientip, request
| filter clientip = "203.0.113.5"
| stats count() by request

Creating a Dashboard

Bash
aws cloudwatch put-dashboard   --dashboard-name production   --dashboard-body '{
    "widgets": [{
      "type": "metric",
      "properties": {
        "title": "EC2 CPU",
        "metrics": [["AWS/EC2","CPUUtilization","InstanceId","i-xxxxxxxx"]],
        "period": 300,
        "stat": "Average",
        "view": "timeSeries"
      }
    }]
  }'
#aws#cloudwatch#metrics
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