EC2 vs ECS vs EKS – Latest Interview Questions Every DevOps Engineer Must Know
Introduction
Understanding the differences between EC2, ECS, and EKS is crucial for any DevOps engineer working with AWS. These three services represent different levels of abstraction for running applications in the cloud, and knowing when to use each is a key skill that interviewers assess. This guide covers the most important interview questions you’ll encounter.
Understanding the Basics
What is EC2?
Amazon Elastic Compute Cloud (EC2) is AWS’s fundamental compute service that provides virtual servers in the cloud. EC2 gives you complete control over the computing resources and allows you to run any application or workload.
What is ECS?
Amazon Elastic Container Service (ECS) is a fully managed container orchestration service that allows you to run Docker containers on AWS. ECS eliminates the need to manage your own container orchestration infrastructure.
What is EKS?
Amazon Elastic Kubernetes Service (EKS) is a managed Kubernetes service that makes it easy to run Kubernetes on AWS without needing to install and operate your own Kubernetes control plane.
Top Interview Questions and Answers
1. What are the key differences between EC2, ECS, and EKS?
Answer:
EC2 provides raw compute capacity where you manage everything from the operating system up. You have full control but also full responsibility for patching, scaling, and maintenance.
ECS is a container orchestration service built by AWS. It abstracts away much of the infrastructure management while giving you the ability to run containerized applications. You can use EC2 instances or AWS Fargate as the compute engine.
EKS is AWS’s managed Kubernetes service. It provides the same container orchestration capabilities as ECS but uses the industry-standard Kubernetes API. This makes it portable across different cloud providers and on-premises environments.
2. When would you choose EC2 over ECS or EKS?
Answer:
Choose EC2 when you need:
- Complete control over the operating system and infrastructure
- To run legacy applications that aren’t containerized
- Custom software that requires specific OS-level configurations
- Maximum flexibility with minimal abstraction
- To run applications that don’t benefit from containerization
3. What are the advantages of using ECS over plain EC2?
Answer:
ECS provides several advantages:
- Built-in container orchestration without managing additional software
- Automatic load balancing and service discovery
- Native integration with AWS services like IAM, CloudWatch, and Load Balancers
- Simpler deployment and scaling of containerized applications
- Option to use Fargate for serverless container execution
- Task definitions for declarative application configuration
- Lower operational overhead compared to managing containers on EC2 directly
4. Why would you choose EKS over ECS?
Answer:
Choose EKS when you need:
- Industry-standard Kubernetes API and ecosystem
- Portability across multiple cloud providers or hybrid environments
- Access to the vast Kubernetes tooling and community
- Multi-cloud or cloud-agnostic strategy
- Advanced Kubernetes features not available in ECS
- Teams already experienced with Kubernetes
- Complex microservices architectures requiring Kubernetes-specific features
5. What is AWS Fargate and how does it relate to ECS and EKS?
Answer:
AWS Fargate is a serverless compute engine for containers that works with both ECS and EKS. Instead of managing EC2 instances, Fargate allows you to run containers without provisioning or managing servers. You simply define your application requirements, and Fargate handles the infrastructure.
Benefits include:
- No server management required
- Pay only for the resources your containers use
- Automatic scaling and high availability
- Improved security through task isolation
- Reduced operational complexity
6. How do you implement auto-scaling in ECS?
Answer:
ECS offers multiple auto-scaling mechanisms:
Service Auto Scaling: Uses Application Auto Scaling to adjust the desired task count based on CloudWatch metrics like CPU or memory utilization, or custom metrics.
Cluster Auto Scaling: When using EC2 launch type, you can use Capacity Providers with Auto Scaling Groups to automatically scale the underlying EC2 instances based on task requirements.
Target Tracking: Scale based on a target value for a specific metric (e.g., maintain 70% CPU utilization).
Implementation involves defining scaling policies with minimum, maximum, and desired task counts, along with CloudWatch alarms that trigger scaling actions.
7. What are ECS Task Definitions and Services?
Answer:
Task Definition: A JSON blueprint that describes how a container should be launched. It includes:
- Container image to use
- CPU and memory requirements
- Port mappings
- Environment variables
- Volume configurations
- Logging configuration
- IAM role for tasks
Service: Maintains a specified number of task instances running simultaneously. Services provide:
- Load balancing across tasks
- Auto-scaling capabilities
- Rolling updates and deployments
- Integration with ELB/ALB
- Service discovery
8. Explain the difference between ECS Launch Types: EC2 vs Fargate
Answer:
EC2 Launch Type:
- You manage the underlying EC2 instances
- Greater control over instance types and configurations
- Can use Reserved Instances or Spot Instances for cost optimization
- Requires managing cluster capacity and patching
- Better for long-running, predictable workloads
Fargate Launch Type:
- AWS manages the infrastructure
- Serverless experience
- Pay per task based on vCPU and memory
- Ideal for variable or unpredictable workloads
- Reduced operational overhead
- Faster time to market
9. What are the cost implications of choosing EC2, ECS, or EKS?
Answer:
EC2: You pay for the instances you run. Costs are predictable with Reserved Instances but you’re responsible for optimization.
ECS: No additional charge beyond the EC2 instances or Fargate resources you use. With Fargate, you pay for vCPU and memory resources your tasks use.
EKS: Charges $0.10 per hour per cluster for the control plane, plus the cost of EC2 instances or Fargate tasks. This makes EKS more expensive than ECS for small deployments, but the cost becomes negligible for larger clusters.
Cost optimization strategies include using Spot Instances, right-sizing resources, implementing auto-scaling, and choosing the appropriate pricing model.
10. How do you manage secrets in ECS and EKS?
Answer:
ECS:
- AWS Secrets Manager integration for secure secret retrieval
- Systems Manager Parameter Store for configuration and secrets
- Secrets can be injected as environment variables at task launch
- IAM roles for tasks provide secure access to secrets
- Encrypted environment variables in task definitions
EKS:
- Kubernetes Secrets for native secret management
- AWS Secrets Manager integration through External Secrets Operator
- Sealed Secrets for GitOps workflows
- IAM Roles for Service Accounts (IRSA) for pod-level IAM permissions
- Third-party solutions like HashiCorp Vault
11. What is a Capacity Provider in ECS?
Answer:
Capacity Providers determine the infrastructure that tasks use. They provide:
Auto Scaling Group Capacity Provider: Manages EC2 instances for your tasks, automatically scaling the cluster based on task requirements.
Fargate Capacity Provider: Uses Fargate for serverless task execution.
Benefits:
- Automatic cluster scaling
- Cost optimization through better resource utilization
- Flexibility to mix EC2 and Fargate tasks
- Simplified capacity management
- Weight-based task distribution across providers
12. How do you implement service discovery in ECS and EKS?
Answer:
ECS:
- AWS Cloud Map integration for DNS-based service discovery
- Service Discovery namespace creation
- Automatic DNS record management
- Health checks for service endpoints
- Integration with Route 53 for private DNS
EKS:
- Kubernetes Service objects with ClusterIP
- CoreDNS for internal service discovery
- AWS Cloud Map integration
- Ingress controllers for external access
- Service mesh solutions like Istio or App Mesh for advanced routing
13. What are the networking differences between ECS and EKS?
Answer:
ECS Networking:
- Task networking modes: bridge, host, awsvpc, none
- awsvpc mode gives each task its own ENI and IP
- Security groups can be applied at task level
- Simpler networking model
- Native AWS networking integration
EKS Networking:
- Uses CNI (Container Network Interface)
- Each pod gets an IP from the VPC subnet
- Network policies for pod-to-pod communication
- More complex but more flexible
- Support for multiple CNI plugins
- Service mesh capabilities for advanced routing
14. How do you handle logging and monitoring in these services?
Answer:
EC2:
- CloudWatch Logs agent installation required
- Custom metrics through CloudWatch
- Manual configuration of log streams
- Third-party agents like Datadog or Splunk
ECS:
- Native CloudWatch Logs integration
- FireLens for flexible log routing
- Container insights for detailed metrics
- Automatic log group creation
- X-Ray integration for distributed tracing
EKS:
- Container insights for cluster monitoring
- Fluent Bit or Fluentd for log aggregation
- Prometheus and Grafana for metrics
- X-Ray or Jaeger for distributed tracing
- CloudWatch Container Insights
15. What are the security best practices for ECS and EKS?
Answer:
ECS Security:
- Use IAM roles for tasks instead of embedding credentials
- Enable task-level security groups with awsvpc mode
- Scan container images for vulnerabilities
- Use private repositories in ECR
- Implement least privilege access
- Enable encryption for data at rest and in transit
- Regular patching of container images
EKS Security:
- Use IAM Roles for Service Accounts (IRSA)
- Implement Pod Security Standards
- Network policies for pod isolation
- Regular Kubernetes version updates
- Use AWS Security Groups for pods
- Enable audit logging
- Implement admission controllers
- Use container runtime security tools
16. How do you perform blue-green deployments in ECS?
Answer:
Blue-green deployments in ECS can be implemented through:
Using CodeDeploy:
- Create two target groups in ALB
- Deploy new version to green environment
- CodeDeploy shifts traffic gradually
- Automatic rollback on failures
Manual Process:
- Create new task definition with updated image
- Create new service with new tasks
- Update ALB to route traffic to new service
- Monitor and switch traffic
- Decommission old service
Benefits: Zero downtime, easy rollback, testing in production environment before full deployment.
17. What is the EKS control plane and data plane?
Answer:
Control Plane:
- Managed by AWS
- Runs Kubernetes API server, etcd, scheduler, and controller manager
- Highly available across multiple AZs
- AWS handles patching and upgrades
- You pay per cluster hour
Data Plane:
- Your worker nodes (EC2 or Fargate)
- Runs your containerized applications
- You manage node upgrades and patching (EC2)
- You pay for compute resources
This separation ensures Kubernetes control plane availability while giving you flexibility over workload infrastructure.
18. How do you upgrade EKS clusters?
Answer:
EKS cluster upgrades involve:
- Control Plane Upgrade: Update through AWS Console, CLI, or Infrastructure as Code. AWS handles the upgrade with no downtime.
- Node Group Upgrade:
- Managed node groups can be updated with a single command
- Self-managed nodes require creating new launch configurations
- Rolling update strategy to maintain availability
- Best Practices:
- Test in non-production environments first
- Review Kubernetes changelog for breaking changes
- Update add-ons after cluster upgrade
- Update kubectl and other tools
- Plan for application compatibility
- Use managed node groups for easier upgrades
19. What are ECS Task Placement Strategies?
Answer:
Task placement strategies determine how ECS places tasks on container instances:
Binpack: Places tasks based on least available CPU or memory, maximizing resource utilization and minimizing the number of instances needed.
Random: Places tasks randomly across available instances.
Spread: Distributes tasks evenly based on a specified value (e.g., availability zone, instance ID) for high availability.
You can combine multiple strategies with constraints like:
- distinctInstance: Don’t place on same instance
- memberOf: Place on instances matching an expression
- attribute-based constraints for fine-grained control
20. Explain the difference between ECS and EKS from an operational perspective
Answer:
ECS – Simpler Operations:
- AWS-native, tightly integrated with AWS services
- Simpler learning curve
- Less configuration required
- Easier for teams new to containers
- Limited to AWS ecosystem
- Good for straightforward container workloads
EKS – More Complex but Powerful:
- Requires Kubernetes expertise
- More configuration and operational overhead
- Portable across clouds and on-premises
- Rich ecosystem of tools and add-ons
- Better for complex microservices architectures
- Steeper learning curve but more flexibility
- Better for organizations with existing Kubernetes investment
Conclusion
Mastering EC2, ECS, and EKS is essential for modern DevOps engineering. Each service has its place in cloud architecture, and understanding when to use each demonstrates your architectural expertise. Use this guide to prepare for your interviews and deepen your understanding of AWS compute services.
Remember, the best service depends on your specific requirements: team expertise, application architecture, cost constraints, and operational capabilities. There’s no one-size-fits-all answer, and interviewers appreciate candidates who understand these nuances.
CloudSoftSol – Your partner in cloud excellence and DevOps transformation.
