Each test is 5 questions with varying difficulty.
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Choosing between AWS EC2, Fargate, and Lambda is a fundamental architectural decision that defines the scalability, cost, and operational overhead of cloud-native applications in 2026. This topic is a staple in system design and cloud engineering interviews, requiring candidates to demonstrate a deep understanding of the abstraction layers provided by each service. Junior engineers are expected to identify the primary use cases for each, while senior engineers must articulate the nuanced tradeoffs regarding state management, cold start latency, networking constraints, and long-term cost efficiency. Interviewers use this topic to gauge your ability to map business requirements—such as traffic patterns, execution duration, and regulatory compliance—to the appropriate compute primitive. Mastery involves knowing when to sacrifice control for speed (Lambda), when to balance orchestration with abstraction (Fargate), and when the granular control of virtualized hardware (EC2) is non-negotiable.
In 2026, the compute landscape is defined by the tension between operational velocity and infrastructure efficiency. Understanding the distinction between EC2, Fargate, and Lambda is critical because misaligned choices lead to either 'over-provisioning tax' or 'architectural rigidity.' For instance, running a steady-state, high-throughput service on Lambda often results in significantly higher costs compared to Fargate or reserved EC2 instances due to the premium paid for event-driven abstraction. Conversely, choosing EC2 for bursty, unpredictable workloads introduces unnecessary maintenance burdens like patching, OS hardening, and scaling policy management. This topic is a high-signal interview area because it tests your 'architectural intuition.' A strong candidate doesn't just list features; they discuss the 'operational tax' of managing an OS (EC2) versus the 'platform constraints' of serverless (Lambda/Fargate). They can explain why a 15-minute execution limit in Lambda might force a migration to Fargate, or how VPC networking overhead in Lambda can impact latency-sensitive microservices. This depth distinguishes engineers who build 'just enough' infrastructure from those who over-engineer or under-provision.
The compute hierarchy ranges from raw virtualized hardware (EC2) to container-orchestrated abstraction (Fargate) and event-driven runtime (Lambda). EC2 requires manual lifecycle management, Fargate abstracts the cluster control plane, and Lambda abstracts the entire execution environment.
Incoming requests are routed via Load Balancers to either an EC2 instance, a Fargate task, or a Lambda function, each interacting with the VPC via different networking interfaces.
User Request
↓
[Load Balancer]
↓
-----------------------------------
↓ ↓ ↓
[EC2] [Fargate] [Lambda]
↓ ↓ ↓
[OS/Kernel] [Container Runtime] [Firecracker VM]
↓ ↓ ↓
[VPC/ENI] [VPC/ENI] [Hyperplane ENI]Using Lambda for bursty event-driven tasks and Fargate for steady-state API services within the same VPC.
Trade-offs: Increases architectural complexity but optimizes cost and performance.
Deploying a logging or proxy container alongside the main application container in Fargate tasks.
Trade-offs: Improves modularity but increases resource consumption per task.
Pre-warming Lambda execution environments to eliminate cold starts for latency-sensitive traffic.
Trade-offs: Eliminates cold starts but incurs fixed hourly costs.
| Reliability | EC2 requires auto-scaling groups and multi-AZ deployment. Fargate handles task replacement automatically. Lambda provides built-in high availability across AZs. |
| Scalability | Lambda scales per request. Fargate scales via ECS Service Auto Scaling. EC2 scales via ASG based on custom CloudWatch metrics. |
| Performance | EC2 offers lowest latency for compute-intensive tasks. Fargate has minimal overhead. Lambda has cold start overhead. |
| Cost | EC2 is cheapest for steady-state. Fargate is mid-range. Lambda is cheapest for low-traffic or highly bursty workloads. |
| Security | EC2 requires full OS hardening. Fargate and Lambda provide managed security environments with reduced attack surfaces. |
| Monitoring | Use CloudWatch metrics for all. X-Ray is essential for distributed tracing in serverless architectures. |
No. Lambda is cost-effective for bursty or low-traffic workloads. For steady-state, high-throughput applications, EC2 or Fargate are usually significantly cheaper due to the premium paid for serverless abstraction.
Fargate supports most standard Docker containers, but it does not support privileged containers or those requiring direct kernel access, which might be necessary for certain security or monitoring tools.
EC2 requires you to manage the underlying EC2 instances (patching, scaling, OS hardening) that run your containers, whereas Fargate manages the compute capacity for you, abstracting away the server layer entirely.
Lambda is stateless. You must externalize state to services like DynamoDB, ElastiCache (Redis), or S3. Any data stored in the local /tmp directory is only available for the duration of the execution.
Fargate tasks have a startup time associated with pulling the image and initializing the container, but it is generally more predictable than Lambda's cold start, which involves initializing the entire runtime environment.
Choose EC2 when you need full control over the OS, specific kernel tuning, specialized hardware (like GPUs or FPGAs), or if you need to optimize costs for long-running, high-utilization workloads using Reserved Instances.
Lambda natively supports several languages, but you can use custom runtimes to execute any language that can run on Amazon Linux, provided it fits within the execution environment constraints.
Use VPC security groups, IAM roles for task/function execution, and PrivateLink for accessing AWS services without traversing the public internet.
Yes, this is a common pattern. You might use Lambda for event-driven processing, Fargate for API services, and EC2 for specialized background processing or legacy components, all connected via a shared VPC.
The maximum execution time for a Lambda function is 15 minutes. If your process takes longer, you must migrate to Fargate or EC2.
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