AWS CDK Infrastructure Best Practices

TypeScript

• Use strict type checking
• Import from aws-cdk-lib and constructs
• Use L2 constructs when available, L1 (Cfn*) when necessary

Architecture — Single Stack

The entire application is provisioned by one CDK stack (PlatformStack). Application code is shipped out-of-band via AWS APIs (ECR push → ECS service update / Lambda code update / AgentCore Runtime update).

infrastructure/
├── bin/infrastructure.ts          # App entrypoint (instantiates PlatformStack)
├── lib/
│   ├── platform-stack.ts          # The one stack — all infrastructure
│   ├── config.ts                  # Configuration loader & validator
│   └── constructs/                # 39 reusable CDK constructs
│       ├── network/               # VPC, ALB, ECS cluster
│       ├── identity/              # Cognito, secrets, KMS, OAuth
│       ├── data/                  # DynamoDB tables, file uploads
│       ├── rag/                   # RAG documents, vectors
│       ├── rag-ingestion/         # RAG ingestion Lambda
│       ├── artifacts/             # Artifact rendering pipeline
│       ├── mcp-sandbox/           # MCP Apps sandbox proxy
│       ├── agentcore/             # Memory, Code Interpreter, Browser, Gateway
│       ├── inference-api/         # AgentCore Runtime
│       ├── app-api/               # Fargate service
│       ├── fine-tuning/           # SageMaker IAM
│       ├── spa/                   # SPA CloudFront distribution
│       └── zones/                 # Route53, ALB DNS
└── cdk.context.json               # Configuration defaults

Key principle: CDK deploys are rare (infrastructure changes only). Day-to-day code changes deploy via backend.yml (AWS API calls, no CDK).

Configuration

Use the centralized config system:

import { loadConfig, getResourceName, getStackEnv, applyStandardTags } from './config';

PlatformStack receives config via props:

const config = loadConfig(app);
new PlatformStack(app, `${config.projectPrefix}-PlatformStack`, { config, env });

For configuration patterns, see references/configuration.md.

Naming Conventions

Resource Names: Use getResourceName():

getResourceName(config, 'user-quotas')  // "bsu-agentcore-user-quotas"

SSM Parameters: Hierarchical naming for runtime consumption:

/{projectPrefix}/{category}/{resource-type}

Categories: /network/, /quota/, /cost-tracking/, /auth/, /frontend/, /gateway/, /rag/, /artifacts/

Cross-Construct References

Since everything is in one stack, use typed props — not SSM:

// In PlatformStack:
const network = new NetworkConstruct(this, 'Network', { config });
new AlbConstruct(this, 'Alb', { config, vpc: network.vpc });

SSM parameters are published only for runtime consumption by ECS tasks and Lambdas — never for CDK-to-CDK references within the same stack.

Wire a resource's name to every compute that reads it

When a construct exposes a table/bucket that backend code reads via os.environ.get("X_NAME", "default"), you must set X_NAME in the container environment of every compute that runs that code — thread the typed ref through that compute's env builder (e.g. buildAppApiEnvironment for app-api, the inference-agentcore construct's environment for inference-api). Wiring one does not wire the other.

Why this bites (silent 502): the backend's default fallback hides the omission. If the env var is missing, the code queries the default name (e.g. "memory-spaces" instead of {prefix}-memory-spaces), the resource isn't found, boto3 raises ResourceNotFoundException, and the centralized handler (apis/shared/security/error_handler.py) maps it to a generic 502 {"detail":"Upstream service error."}. Nothing in cdk synth or CI catches it — the stack is valid, the IAM grant may even exist; only a runtime read fails. (Real instance: PR #588 — memory-spaces names were wired to inference-api but not app-api, which owns the CRUD routes.)

Guard it: add an env-map unit test asserting the key is emitted (see test/app-api-environment.test.ts). Mind the boundary: app-api owns user-facing CRUD; granting IAM or wiring inference-api does not cover it.

DynamoDB Tables

• Always use PK + SK for flexibility
• Use PAY_PER_REQUEST billing
• Enable point-in-time recovery
• Environment-based removal policy

For table patterns, see references/dynamodb.md.

ECS/Fargate

• Cluster created by NetworkConstruct, referenced via typed prop
• Health checks mandatory
• Auto-scaling with CPU/memory targets
• Circuit breaker for rollback
• Bootstrap container pattern: CDK creates the service with a placeholder image; the backend workflow pushes the real image via update-service

For service patterns, see references/ecs-fargate.md.

Lambda

• Use ARM64 architecture (cost optimization)
• Role with least privilege
• Secrets Manager access requires wildcard suffix
• Bootstrap pattern: CDK creates the function with placeholder code; the backend workflow pushes real code via update-function-code

For Lambda patterns, see references/lambda.md.

S3 Buckets

• Block public access
• Enable versioning
• Lifecycle rules for cost optimization
• Include account ID for global uniqueness

For bucket patterns, see references/s3.md.

Security

• Separate security groups for ALB and ECS
• Private subnets for services
• IAM roles with SIDs for clarity
• Never hardcode secrets

For IAM patterns, see references/iam.md.

Important Constraints

AgentCore Names: Use underscores, not hyphens:

name: getResourceName(config, 'memory').replace(/-/g, '_')

Secrets Manager ARN: Include wildcard for random suffix:

resources: [`${secret.secretArn}*`]

Removal Policy:

removalPolicy: getRemovalPolicy(config)  // RETAIN in prod, DESTROY in dev

CDK Commands

cd infrastructure
npm ci                # Install dependencies
npx cdk synth         # Synthesize CloudFormation
npx cdk deploy {prefix}-PlatformStack  # Deploy
npx cdk diff          # Preview changes