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Amazon EC2 — Elastic Compute: When to Use What (and How the Exam Tests It)
Understand when to choose Amazon EC2 and how the SAA-C03 exam tests your knowledge on this topic.
Amazon EC2 offers virtual machines that you control at the OS level. You pay for what you use, with billing per second across numerous instance families. This flexibility is powerful but requires careful decision-making.
When to Choose EC2
Full Control of the OS
If you need complete control over the operating system or kernel, EC2 is your choice. This is essential for applications requiring custom configurations or long-running processes.
Lift-and-Shift Migration
For organizations moving existing workloads to the cloud, EC2 allows a straightforward lift-and-shift approach. You can replicate your on-premises environment without significant changes.
Managing Workloads
EC2 suits steady or spiky workloads. With Auto Scaling groups, you can manage scaling dynamically. This is ideal for applications with fluctuating demand.
Workload Characteristics
| Instance Family | Workload Type |
|---|---|
| t/m | General Purpose |
| c | Compute-Bound |
| r/x | Memory-Bound |
| i/d | Storage-Heavy |
| g/p | GPU-Intensive |
Key Architectural Decisions
Pricing Strategies
- On-Demand: Best for spiky workloads with no long-term commitment.
- Savings Plans/Reserved Instances: Cost-effective for consistent baseline demand.
- Spot Instances: Ideal for fault-tolerant batch jobs, as they offer significant savings for interruptible workloads.
Availability Zones
Never pin production workloads to a single Availability Zone (AZ). Always distribute instances across multiple AZs to ensure fault tolerance and high availability. Use a load balancer to manage traffic.
Gotchas & Exam Traps
Ephemeral Data
Remember, instance store data is ephemeral. If you stop or terminate an instance, the data is lost. Always use EBS for persistent storage needs.
Security Groups vs. NACLs
Security groups are stateful. This means if you allow inbound traffic, the response is automatically allowed. In contrast, Network Access Control Lists (NACLs) are stateless and require explicit rules for both inbound and outbound traffic.
Spot Instances
The exam may present scenarios where you need to identify the most cost-effective option for a fault-tolerant batch job. Spot Instances are often the correct answer.
How the Exam Tests This
Questions related to EC2 often follow specific patterns:
- Scenario-Based Questions: These require you to choose the best instance type based on workload characteristics. Pay attention to the nuances of workload needs.
- Pricing Questions: Expect questions about when to use On-Demand, Reserved, or Spot pricing based on provided scenarios.
- Architectural Decision Questions: You might encounter questions assessing your understanding of multi-AZ deployments versus single-AZ deployments.
The Rule to Remember
Choose EC2 for full OS control, migration, or managing variable workloads; consider alternatives for event-driven scenarios.
For practice, check out our resources to solidify your knowledge. Take the free SAA-C03 mock exam.