Development with AWS Services Study Guide — DVA-C02

Development with AWS Services – Study Guide (DVA-C02)

This domain covers 32% of the exam and tests your ability to select, configure, and integrate AWS developer services into serverless, event-driven, and containerised architectures. Expect scenario-based questions requiring you to choose between similar services, debug integration issues, and apply the right concurrency or caching strategy.

AWS Lambda

Configuration limits: 15-minute max timeout, 10 GB memory, 250 MB deployment package (unzipped), 512 MB–10 GB /tmp storage. Layers add up to 5 layers per function; total unzipped size including layers must stay under 250 MB.

Cold starts: Happen when no warm execution environment exists. Mitigate with provisioned concurrency (pre-initialised environments, costs money) or keep functions warm via scheduled pings. Reserved concurrency caps a function's maximum concurrency but does not eliminate cold starts.

Concurrency math: concurrency = invocations per second × average duration in seconds. Account default is 1,000 concurrent executions (soft limit). Reserved concurrency subtracts from the account pool; provisioned concurrency is pre-paid capacity within the reserved limit.

Execution role: The Lambda function's IAM role. Permissions to call other AWS services must be on this role, not the caller's role.

Lambda Layers: Share libraries/dependencies across functions. Referenced by ARN. Runtime code is separate from layers.

Lambda Triggers & Event Source Mappings

Critical trap: SQS visibility timeout must be longer than the Lambda timeout or messages reappear mid-processing.

Amazon API Gateway

Three API types:

• REST API – Full features: caching, request validation, usage plans, WAF integration.
• HTTP API – Lower latency, cheaper (~70% less), supports OIDC/JWT auth, no usage plans or caching.
• WebSocket API – Persistent connections, route selection expressions, @connections management.

Stages & deployments: Changes require a new deployment to a stage. Stage variables act like environment variables per stage. Canary deployments split traffic between stage versions.

Throttling: Default 10,000 RPS burst, 5,000 RPS steady state per account/region. Usage plans apply per API key. 429 = throttled.

Caching: REST API only. TTL 0–3,600 seconds. Invalidated per-request with Cache-Control: max-age=0 header (requires IAM permission).

CORS: Must be enabled on API Gateway when a browser calls across origins. For Lambda proxy integration, the function must also return CORS headers.

Amazon DynamoDB

Partition key selection: Choose high-cardinality attributes to distribute load evenly. Hot partitions cause ProvisionedThroughputExceededException.

GSI vs LSI:

• LSI – Same partition key, alternate sort key. Created at table creation only. Shares table RCU/WCU.
• GSI – Different partition key and/or sort key. Added anytime. Has its own RCU/WCU. Supports eventual consistency only.

Key API operations:

• GetItem / PutItem / UpdateItem – Single item, eventually or strongly consistent reads.
• Query – Requires partition key; filters on sort key. More efficient than Scan.
• Scan – Reads entire table; expensive. Use FilterExpression to reduce returned data (but RCU still consumed for full scan).
• BatchWriteItem – Up to 25 items per call; no partial failure rollback.
• TransactWriteItems – ACID across up to 100 items, same or different tables; costs 2× WCU.