05-app-inspector

Module 05 — App Inspector

LocalStack App Inspector gives you a visual, real-time view of your serverless application: service topology, request traces, and event flows — without any instrumentation code.

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Open App Inspector

App Inspector is available in the LocalStack Web App:

1. Go to https://app.localstack.cloud → App Inspector
2. Select your LocalStack instance (should auto-detect if running locally)
3. You'll see the Order Processing Pipeline topology automatically discovered

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Topology View

After running module 01, App Inspector shows:

[API Gateway: orders-api]
    └─▶ [Lambda: order-handler]
            ├─▶ [DynamoDB: orders]
            └─▶ [SQS: orders-queue]
                    └─▶ [Lambda: order-processor]
                                ├─▶ [DynamoDB: orders]  (UpdateItem)
                                └─▶ [S3: order-receipts]
                    [SQS: orders-dlq]  ← (on failure)

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Trace the Happy Path

1. Send an order:

   API=$(cd ../01-serverless-app/terraform && tflocal output -raw api_endpoint)
   curl -X POST "$API/orders" -H "Content-Type: application/json" \
     -d '{"item": "inspector demo", "quantity": 1}'

2. In App Inspector → Traces tab, find the trace for your request
3. Click through to see: API GW → Lambda cold start → DynamoDB write → SQS publish → Lambda invocation → S3 put

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Trace the Chaos Scenario

1. Re-inject the DynamoDB fault (from module 04):

   curl -s -X POST http://localhost:4566/_localstack/chaos/faults \
     -H "Content-Type: application/json" \
     -d @../04-chaos-engineering/faults/ddb-throttle-localstack.json

2. Send a few orders
3. In App Inspector → Traces, look for failed traces (shown in red)
4. Expand a failed trace to see:
   • order-processor Lambda errored with ProvisionedThroughputExceededException
   • SQS retry count incrementing (visible in event metadata)
   • Message eventually routing to orders-dlq
5. Remove the fault and replay — watch the trace go green

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Key App Inspector Features to Explore

Feature	Where
Service topology graph	Overview tab
Per-request traces	Traces tab
Lambda invocation logs	Click a Lambda node → Logs
SQS message flow	Click an SQS node → Messages
DynamoDB operations	Click DynamoDB node → Operations

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Next: Module 06 — AI Integration (optional)