AWS Solutions Architect: Core Compute, Storage & Database Architecture

Overview

Designing resilient, cost-optimized, and highly available architectures on Amazon Web Services (AWS) requires an understanding of how foundational services interact across multiple Availability Zones (AZs).

This study guide summarizes the high-priority architectural patterns, storage classes, and database trade-offs needed for the AWS Solutions Architect exam and real-world team implementations.

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High Availability VPC Architecture

A production-grade VPC is split across at least two Availability Zones with dedicated public and private subnets.

       Internet
          │
    ┌─────▼─────────────────────────┐
    │     Internet Gateway (IGW)    │
    └─────┬───────────────────┬─────┘
          │                   │
  ┌───────▼────────┐  ┌───────▼────────┐
  │ Public Subnet  │  │ Public Subnet  │
  │ AZ-1a (NAT GW) │  │ AZ-1b (NAT GW) │
  └───────┬────────┘  └───────┬────────┘
          │ (Egress Traffic)  │
  ┌───────▼────────┐  ┌───────▼────────┐
  │ Private Subnet │  │ Private Subnet │
  │ AZ-1a (App/DB) │  │ AZ-1b (App/DB) │
  └────────────────┘  └────────────────┘

Key VPC Design Rules:

1. Public Subnet: Has a direct route table entry to an Internet Gateway (0.0.0.0/0 -> igw-xxxx).
2. Private Subnet: Reaches the internet outbound only via a NAT Gateway located in a public subnet.
3. Security Groups vs. NACLs:
   • Security Groups: Stateful, apply at instance/ENI level, allow rules only.
   • NACLs: Stateless, apply at subnet level, support allow and deny rules evaluated in numbered order.

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EC2 Purchasing & Scaling Strategies

Selecting the right purchasing option can reduce compute costs by up to 90%:

Option	Best Use Case	Discount
On-Demand	Short-term, spiky, unpredictable workloads	Baseline (0%)
Reserved Instances (1 or 3 yr)	Steady-state database / baseline compute	Up to 72%
Savings Plans	Flexible compute usage across EC2, Fargate, Lambda	Up to 72%
Spot Instances	Fault-tolerant batch processing, big data, CI/CD	Up to 90%

Pro Tip: Never run mission-critical relational database masters on Spot Instances since AWS can reclaim spot capacity with a 2-minute termination notice.

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Amazon S3 Storage Tier Decision Matrix

Choosing the correct S3 storage class directly impacts both retrieval latency and cost:

• S3 Standard: 99.99% availability, 11 9s durability. Millisecond retrieval. For active data.
• S3 Standard-IA (Infrequent Access): Lower storage cost, but incurs per-GB retrieval fees. 30-day minimum storage charge.
• S3 Intelligent-Tiering: Automatically moves objects between frequent, infrequent, and archive access tiers based on access patterns without operational overhead.
• S3 Glacier Flexible: Retrieval in minutes to hours. Ideal for quarterly backups.
• S3 Glacier Deep Archive: Lowest cost cloud storage ($0.00099/GB/mo). Retrieval within 12 to 48 hours.

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Database Architecture: RDS vs DynamoDB

Relational Database Service (RDS / Aurora)

• Use Cases: Complex joins, ACID transactions, relational models (Postgres, MySQL).
• Multi-AZ: Synchronous standby replica in another AZ for instant automatic failover.
• Read Replicas: Asynchronous replication for horizontal read scaling (up to 15 Aurora replicas).

Amazon DynamoDB

• Use Cases: Key-value or document model with predictable single-digit millisecond latency at any scale.
• Partition Key & Sort Key: Careful partition key selection ensures uniform partition distribution and prevents hot partition throttling.
• DAX (DynamoDB Accelerator): In-memory cache delivering microsecond latency for read-heavy workloads.

# Example: Querying a DynamoDB table via AWS CLI
aws dynamodb query \
    --table-name CloudStudyNotes \
    --key-condition-expression "Category = :cat AND Date >= :dt" \
    --expression-attribute-values '{
        ":cat": {"S": "AWS"},
        ":dt": {"S": "2026-01-01"}
    }'

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Key Exam & Interview Checklist

• Multi-AZ deployments protect against infrastructure failure (High Availability).
• Read Replicas improve read performance (Scalability).
• S3 Cross-Region Replication (CRR) requires Versioning enabled on both source and destination buckets.
• Use AWS Secrets Manager for automatic credential rotation with RDS.