CloudWatch Logs

Where applications and AWS services send their log lines.

Think of it as: The building's logbook.

What to know for Level 0

Logs go into log groups (one per app or function). Each group holds log streams, one per source, such as a container or a Lambda instance.
Log groups keep data forever by default. Set a retention period (say 30 days) and older events are deleted for you.
You can search and query a log group (Logs Insights), and a metric filter turns matching lines into a number you can set an alarm on.
CloudWatch Logs holds what your software printed; CloudTrail holds who did what to AWS.
Never log secrets: anyone allowed to read the log group can read them.

More detail

Logs are grouped into log groups (one per app or function) and log streams. You can search them, set how long to keep them and raise alarms on them. Don’t confuse this with CloudTrail, which records AWS API calls (who did what to AWS), not your app’s output.

Quiz yourself on CloudWatch Logs →

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