Review SAO & Define Infra Requirements

Objective

Read docs/architecture/SAO.md, identify the AWS services needed for the application, and produce a concise infrastructure requirements document that drives all subsequent CDK stack decisions.

Process

1. Read SAO.md

Extract from SAO.md:

• Technology Stack Table — runtime versions, databases, caches, queues
• § Deployment Strategy (DTA-14) — blue/green, canary, rolling
• § Infrastructure (DTA-15) — cloud provider, region, compute platform
• § Observability (DTA-13) — logging, metrics, tracing services

2. Map Application Needs → AWS Services

3. Choose Deployment Style

Read the infrastructure skills available in this playbook. Pick one based on SAO.md § Deployment Strategy and § Infrastructure decisions:

Record the choice in INFRA_REQUIREMENTS.md under a new "Deployment Style" heading:

## Deployment Style

**Chosen**: [EKS / Elastic Beanstalk]

**Rationale**: [Why this style fits the project — team size, service count, K8s familiarity, etc.]

**Skill Reference**: [Skill name and ID]

All subsequent DCI and DCD activities must be executed using the patterns from the chosen skill.

4. Document Infra Requirements

Create docs/architecture/INFRA_REQUIREMENTS.md. Tailor the content to your chosen deployment style:

EKS Path

# Infrastructure Requirements

## AWS Region
{region from SAO.md, e.g., us-east-1}

## Deployment Style
**Chosen**: Kubernetes / EKS
**Rationale**: Multi-service architecture with microservices orchestration needs
**Skill Reference**: K8s in EKS Deployment Patterns (#23)

## Services Required
| Service | Purpose | Configuration |
|---------|---------|---------------|
| VPC | Network isolation | 2 public + 2 private subnets, NAT GW |
| EKS | Container orchestration | Managed node group, 2-3 nodes |
| ECR | Container registry | 1 repo per service |
| Route53 | DNS + blue/green switching | Hosted zone, prod/idle weighted records |

## Blue/Green Strategy
- Two namespaces: `blue`, `green`
- Route53 weighted records: `prod.{domain}` → active, `idle.{domain}` → standby
- Switch = swap DNS weights (0/100 ↔ 100/0)

## Cost Estimate
{Rough monthly cost for EKS + NAT + Route53}

## Security Requirements
- Private subnets for EKS nodes
- Security groups: EKS ↔ database, ALB ↔ EKS
- IAM roles: EKS node role, CDK deploy role

EB Path

# Infrastructure Requirements

## AWS Region
{region from SAO.md, e.g., us-east-1}

## Deployment Style
**Chosen**: Elastic Beanstalk
**Rationale**: Single Django application, small team, prefer managed infrastructure
**Skill Reference**: AWS EB Blue/Green Deployment

## Services Required
| Service | Purpose | Configuration |
|---------|---------|---------------|
| VPC | Network isolation | 2 public + 2 private subnets, NAT GW |
| Elastic Beanstalk | Managed Docker platform | 2 environments: {project}-prod, {project}-idle |
| ECR | Container registry | 1 repo for web image |
| S3 | Deployment bundles | elasticbeanstalk-{region}-{account} |

## Blue/Green Strategy
- Two EB environments: `{project}-prod` (physical A), `{project}-idle` (physical B)
- CNAME swap: `swap-environment-cnames` flips prod ↔ idle roles
- Prod is whichever env currently holds the `{project}-prod` CNAME

## Environment Variables
- `EB_APP`: {project}
- `EB_ENV_A`: {project}-prod
- `EB_ENV_B`: {project}-idle
- `EB_BUCKET`: elasticbeanstalk-{region}-{account}

## Cost Estimate
{Rough monthly cost for 2 EB environments + NAT + S3}

## Security Requirements
- Private subnets for EB instances
- Security groups: EB ALB ↔ instances
- IAM roles: EB service role, instance profile

5. Validate with SAO.md

Cross-check: every service in INFRA_REQUIREMENTS.md must trace back to a decision in SAO.md. If SAO.md doesn't cover infra decisions, flag it and update DTA first.

Deliverables

• ✅ SAO.md reviewed — infra-relevant sections extracted
• ✅ Deployment style chosen — EKS or EB, documented with rationale
• ✅ AWS service mapping — application needs → AWS services (both paths shown)
• ✅ docs/architecture/INFRA_REQUIREMENTS.md created (tailored to chosen style)
• ✅ Blue/green strategy documented (style-specific)
• ✅ Cost estimate included

Inputs

Read these before starting this activity. They are produced earlier in the playbook and are authoritative — raise a drift event instead of deviating.

• System Architecture Overview Template (Template, Required) — produced by Write SAO.md (#59).