AWS Lambda CloudWatch AlarmsThresholds, failures, and debugging guides

Errors counts the number of Lambda invocations that resulted in a function error — including exceptions thrown by the function code and runtime errors (timeout, out-of-memory, handler not found).

Duration measures the elapsed wall-clock time from when the Lambda function handler begins executing to when it returns or times out. CloudWatch publishes minimum, maximum, average, and percentile statistics.

Throttles counts invocation requests that Lambda rejected because concurrent execution limits were reached. A throttled invocation was not executed — the caller receives a 429 TooManyRequestsException.

ConcurrentExecutions reports the number of Lambda function instances actively processing events at any given time, across the entire account or per function when filtered by function name.