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4.5.1. Quick Reference: Service Selection

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

ScenarioServiceWhy
Run code in response to events, no serversLambdaServerless compute, pay-per-invocation
REST/HTTP API frontend for LambdaAPI GatewayManaged API with auth, throttling, stages
Key-value lookups, single-digit ms latencyDynamoDBNoSQL, auto-scaling, serverless option
Relational data with joins and transactionsRDS / AuroraSQL, ACID compliance, managed
Store files, images, static assetsS3Object storage, 11 9s durability
Decouple services, guaranteed deliverySQSMessage queue, at-least-once (Standard) or exactly-once (FIFO)
Fan-out notifications to multiple subscribersSNSPub/sub, push to SQS/Lambda/HTTP/email
Event-driven routing with rulesEventBridgeContent-based filtering, cross-account
Orchestrate multi-step workflowsStep FunctionsState machine, error handling, retries
Cache frequently read dataElastiCache / DAXMicrosecond reads, reduce DB load
Store secrets with rotationSecrets ManagerAuto-rotation, RDS integration
Store config values (non-secret)Parameter StoreFree tier, hierarchical, versioned
Authenticate end usersCognito User PoolsManaged auth, JWT tokens, MFA
Federate to AWS servicesCognito Identity PoolsTemporary AWS credentials for users
CI/CD pipeline orchestrationCodePipelineConnects source → build → deploy
Build and test codeCodeBuildManaged build, buildspec.yml
Deploy to EC2/Lambda/ECSCodeDeployBlue/green, canary, rolling
Container image registryECRDocker images, lifecycle policies
Run containers without managing serversFargateServerless containers on ECS
See how it connects
Alvin Varughese
Written byAlvin Varughese
Founder•20 professional certifications