4.5.1. Quick Reference: Service Selection

When the exam asks "which service should you use?" — use this decision matrix:

Scenario	Service	Why
Run code in response to events, no servers	Lambda	Serverless compute, pay-per-invocation
REST/HTTP API frontend for Lambda	API Gateway	Managed API with auth, throttling, stages
Key-value lookups, single-digit ms latency	DynamoDB	NoSQL, auto-scaling, serverless option
Relational data with joins and transactions	RDS / Aurora	SQL, ACID compliance, managed
Store files, images, static assets	S3	Object storage, 11 9s durability
Decouple services, guaranteed delivery	SQS	Message queue, at-least-once (Standard) or exactly-once (FIFO)
Fan-out notifications to multiple subscribers	SNS	Pub/sub, push to SQS/Lambda/HTTP/email
Event-driven routing with rules	EventBridge	Content-based filtering, cross-account
Orchestrate multi-step workflows	Step Functions	State machine, error handling, retries
Cache frequently read data	ElastiCache / DAX	Microsecond reads, reduce DB load
Store secrets with rotation	Secrets Manager	Auto-rotation, RDS integration
Store config values (non-secret)	Parameter Store	Free tier, hierarchical, versioned
Authenticate end users	Cognito User Pools	Managed auth, JWT tokens, MFA
Federate to AWS services	Cognito Identity Pools	Temporary AWS credentials for users
CI/CD pipeline orchestration	CodePipeline	Connects source → build → deploy
Build and test code	CodeBuild	Managed build, buildspec.yml
Deploy to EC2/Lambda/ECS	CodeDeploy	Blue/green, canary, rolling
Container image registry	ECR	Docker images, lifecycle policies
Run containers without managing servers	Fargate	Serverless containers on ECS

Written byAlvin Varughese•Founder•15 professional certifications