Observability And Monitoring Architecture — AWS Developer (DVA-C02)
CloudWatch Aggregates Metrics. X-Ray Traces Requests.
Picking CloudWatch for a 'diagnose latency spike in a distributed call chain' scenario is partially right. CloudWatch metrics aggregate duration, error count, and throttle rate across all invocations in a time window, answering how often a problem happens. X-Ray records a distributed trace with per-segment timing for one specific request as it moves through Lambda, DynamoDB, and any downstream Lambda. CloudWatch surfaces the error rate going up at 14:32. X-Ray surfaces which segment of the failing request at 14:32:17 took 4.2 seconds inside DynamoDB. Structured logs sent to CloudWatch Logs Insights allow ad-hoc queries across invocations when the distributed trace alone does not isolate the root cause.
What This Pattern Tests
The exam describes a diagnostic need and tests which observability tool applies. CloudWatch Metrics provides aggregated health data — CPU utilization, error counts, latency percentiles. CloudWatch Logs captures event-level detail — application errors, access logs, VPC Flow Logs. X-Ray provides distributed request tracing — traces a single request across API Gateway, Lambda, DynamoDB, SQS showing where time is spent. CloudWatch Contributor Insights identifies top talkers. CloudWatch Anomaly Detection spots unusual patterns. The trap is recommending metrics dashboards when the scenario requires tracing a specific slow request through a microservice chain.
Decision Axis
Diagnostic question determines the tool: "Is it healthy?" = Metrics. "What happened?" = Logs. "Where is it slow?" = X-Ray.
Associated Traps
Decision Rules
Whether to anchor the root-cause investigation on the application tier (X-Ray segment duration) or the database tier (CloudWatch CPU utilization) when both signals are simultaneously available.
Whether to emit custom metrics via CloudWatch Embedded Metric Format (structured JSON written to stdout) or via a synchronous PutMetricData SDK call inside the Lambda handler — only EMF satisfies the no-additional-API-call-on-critical-path constraint.
When the symptom is inter-hop latency with no error signals, the correct single action is enabling X-Ray active tracing on both the API Gateway stage and the Lambda function, satisfying the must-instrument-at-code-level and end-to-end-trace-propagation-required constraints simultaneously — CloudWatch solutions fail because they surface aggregate metrics at one boundary without propagating trace context across hops.
Domain Coverage
Difficulty Breakdown