AWS CloudWatch Basics: Metrics, Logs and Alarms for Your Resources

Last time I looked at who changed things with CloudTrail. The next question is different: what is happening inside my resources right now? That is Amazon CloudWatch. What CloudWatch does Metrics: numbers over time, such as EC2 CPU utilization or S3 request counts. Logs: log data from your applications and services, stored in log groups. Alarms: watch a metric and do something when it crosses a threshold. Dashboards: put the graphs you care about on one page. CloudTrail vs CloudWatch Question Service Who made this change? CloudTrail Is this resource healthy and busy? CloudWatch How an alarm works An alarm watches one metric over a period (for example, 5 minutes). Its state is OK, ALARM or INSUFFICIENT_DATA. When the state changes, it can send a message to an SNS topic, which can email you. The threshold and the number of periods to evaluate decide how sensitive it is. Good to know EC2 sends basic metrics every 5 minutes by default, and detailed monitoring gives 1-minute data (extra cost). EC2 does not report memory or disk usage by default. You need the CloudWatch agent for those. Logs stay forever unless you set a retention period, so set one. Hands-on: try it in your own account Open CloudWatch and browse All metrics for EC2 or S3. Choose Alarms, then Create alarm. Pick a metric, such as EC2 CPUUtilization for one instance. Set a threshold, for example greater than 70% for 2 periods. Create or choose an SNS topic with your email, and confirm the subscription email. Save the alarm and check that it shows OK or INSUFFICIENT_DATA at first. Common mistakes Creating alarms with no action, so nobody is told. Forgetting to confirm the SNS email subscription. Expecting memory metrics without the CloudWatch agent. Leaving log groups on never-expire retention. Key takeaways CloudTrail tells you who changed it, CloudWatch tells you how it is doing. Metrics feed alarms, alarms feed SNS, SNS reaches you. Install the agent for memory and disk. Set log retention. Tomorrow I'll look at how to use tags to keep resources organized and costs traceable. Part of #120DaysOfAWS.