70+ Fastly Interview Questions and Answers [Edge Computing – 2025]

Fastly Core Concepts

1. What is the primary role of Fastly in edge computing?

Fastly serves as an edge cloud platform, enabling developers to deploy custom code and configurations at the edge for low-latency processing. It accelerates content delivery, secures applications, and supports serverless functions, aligning with cloud-native observability for monitoring performance in multi-cloud DevOps environments.

2. Why is Fastly preferred for real-time edge logic?

Fastly’s VCL scripting allows instant edge code execution, reducing latency for tasks like personalization or A/B testing. It integrates with CI/CD, enabling rapid deployments and scalable performance in cloud-native architectures for high-traffic applications.

3. When should you use Fastly for CDN acceleration?

Use Fastly for CDN acceleration when applications require dynamic caching, low-latency delivery, and custom routing. It’s ideal for e-commerce or media sites, integrating with automated security workflows in DevOps pipelines.

4. Where does Fastly fit in cloud-native strategies?

• Edge Caching Layer: Stores dynamic content near users.
• Traffic Routing Engine: Optimizes paths across clouds.
• Security Gateway: Filters threats before origin.
• Load Balancer System: Distributes global traffic.
• Monitoring Integration Hub: Connects to observability tools.
• Serverless Compute Module: Executes custom edge code.

5. Who typically manages Fastly configurations?

DevOps engineers, network specialists, and security teams manage Fastly configurations, defining VCL rules, caching policies, and security behaviors. They collaborate with platform teams to align with SLAs in cloud-native DevOps workflows.

6. Which protocols does Fastly support?

• HTTP/2 and HTTP/3: Enables multiplexed, low-latency transfers.
• QUIC Protocol: Reduces connection establishment time.
• TLS 1.3 Encryption: Secures data in transit.
• WebSocket Connections: Facilitates real-time applications.
• DNS over HTTPS: Protects query privacy.
• gRPC Acceleration: Optimizes microservices communication.

7. How does Fastly optimize traffic routing?

Fastly optimizes routing using real-time network intelligence, selecting the fastest paths based on latency and congestion. Its Anycast IP and dynamic mapping ensure efficient global delivery, minimizing delays in cloud-native applications.

8. What is Fastly’s Compute@Edge platform?

Compute@Edge allows serverless code execution at the edge using languages like Rust or JavaScript, reducing latency for dynamic tasks. It aligns with CI/CD pipelines for automated deployments in cloud-native architectures.

• Language Support: Rust, JavaScript, Go, WebAssembly.
• Serverless Execution: Runs code without servers.
• Edge Location Deployment: Global low-latency processing.
• API Integration: Connects to backend services.
• Custom Runtime: Tailored for high-performance tasks.
• Monitoring and Logging: Tracks execution metrics.

9. Why use Fastly for API acceleration?

Fastly accelerates APIs by caching responses, compressing payloads, and optimizing routing. It reduces latency for microservices, supporting high-throughput applications in cloud-native DevOps environments.

10. When would you implement Fastly’s VCL?

Implement VCL for custom edge logic like header manipulation or conditional caching. It’s ideal for dynamic applications, integrating with CI/CD for automated updates in cloud-native systems.

11. Where are Fastly VCL scripts deployed?

• Fastly Control Center: Manages VCL configurations.
• Git Repositories: Enables version control.
• Terraform Configuration Files: Defines scripts as code.
• API Endpoint Calls: Programmatic script updates.
• CI/CD Pipeline Scripts: Automates VCL deployments.
• Kubernetes Manifests: Integrates with clusters.

12. Who develops Fastly VCL scripts?

DevOps engineers and developers write VCL scripts for edge customization, collaborating with security teams for compliance. They ensure performance in cloud-native DevOps workflows.

13. Which languages support Fastly Compute?

• Rust Programming Language: High-performance edge code.
• JavaScript ES Modules: Familiar web development syntax.
• Go Language Support: Efficient for backend logic.
• WebAssembly Binaries: Cross-language execution.
• AssemblyScript: TypeScript-like WebAssembly.
• Wasm Extensions: Custom runtime capabilities.

14. How does Fastly handle content caching?

Fastly handles caching with dynamic rules, supporting VCL for conditional storage. It minimizes origin requests, ensuring low-latency delivery in cloud-native applications.

15. What is Fastly’s role in edge computing?

Fastly enables edge computing by executing custom code at edge locations, reducing latency for dynamic tasks. It supports serverless functions, aligning with edge deployments in cloud-native environments.

Fastly Configuration and VCL

16. Why use VCL for Fastly customization?

VCL allows developers to write custom edge logic for routing, caching, and security, enabling fine-grained control. It integrates with CI/CD, supporting automated updates in cloud-native DevOps workflows.

17. When should you use Fastly’s Next-Gen WAF?

Use Next-Gen WAF for advanced threat protection, combining machine learning and rulesets. It’s ideal for APIs, integrating with automated security in DevOps pipelines.

18. Where are VCL scripts defined?

• Fastly Control Center: Manages VCL configurations.
• Git Repositories: Enables version control.
• Terraform Configuration Files: Defines scripts as code.
• API Endpoint Calls: Programmatic script updates.
• CI/CD Pipeline Scripts: Automates VCL deployments.
• Kubernetes Manifests: Integrates with clusters.

19. Who configures Fastly VCL?

DevOps engineers configure VCL, writing scripts for edge behaviors. They collaborate with security teams to ensure compliance in cloud-native environments.

20. Which VCL subroutines are key?

• vcl_recv: Processes incoming requests.
• vcl_hash: Determines caching keys.
• vcl_hit: Handles cache hits.
• vcl_miss: Manages cache misses.
• vcl_deliver: Prepares response delivery.
• vcl_error: Handles error conditions.

21. How do you test VCL scripts?

Test VCL scripts in staging environments using Fastly’s test service, simulating traffic with curl. Validate logic, monitor metrics, and deploy via CI/CD for reliability in cloud-native applications.

22. What is Fastly’s role in API gateway?

Fastly acts as an API gateway, routing requests, applying security, and caching responses at the edge. It reduces latency, aligning with cloud-native ecosystems for microservices.

23. Why use Fastly for DDoS protection?

Fastly mitigates DDoS by filtering traffic at the edge, using rate limiting and IP reputation. It ensures uptime, integrating with DevOps for automated responses.

24. When would you use Fastly’s Image Optimizer?

Use Image Optimizer for automatic image resizing and format conversion, reducing payload sizes. It’s ideal for mobile sites, integrating with CI/CD for performance tuning.

25. Where are image configs defined?

• Fastly Control Center: Sets optimization rules.
• Terraform Configuration Files: Manages as code.
• Git Repositories: Tracks image policy versions.
• API Endpoint Calls: Programmatic config updates.
• CI/CD Pipeline Scripts: Automates image deployments.
• Kubernetes Manifests: Integrates with clusters.

26. Who optimizes image delivery?

Performance engineers optimize image delivery, tuning resizing and caching rules. They collaborate with DevOps to ensure fast loading in cloud-native media workflows.

27. Which metrics track image performance?

• image_requests_total: Counts image requests.
• image_optimization_savings: Measures bandwidth reduction.
• image_latency_seconds: Tracks delivery time.
• image_cache_hit_ratio: Monitors caching efficiency.
• image_error_rate: Logs optimization failures.
• image_traffic_by_format: Analyzes format distribution.

28. How do you scale image optimization?

Scale image optimization by configuring rules for multiple formats, enabling edge caching, and load-testing in staging. Monitor metrics and update via CI/CD for performance.

29. What is the impact of poor image optimization?

Poor image optimization increases load times and bandwidth usage, degrading user experience. Tune settings, test in staging, and update via Git for smooth delivery in cloud-native workflows.

Fastly Security and WAF

30. Why is Fastly’s Next-Gen WAF effective?

Next-Gen WAF protects against OWASP threats using machine learning and rulesets, filtering malicious traffic at the edge. It ensures secure applications in cloud-native environments.

31. When should you enable Bot Management?

Enable Bot Management for sites facing scraping or abuse, using behavioral analysis to block malicious bots. It protects resources, integrating with DevOps security pipelines.

32. Where are WAF rules configured?

• Fastly Control Center: Defines managed rulesets.
• Terraform Configuration Files: Manages rules as code.
• API Endpoint Calls: Programmatic rule updates.
• Git Repositories: Tracks rule versions.
• CI/CD Pipeline Scripts: Automates rule deployments.
• Kubernetes Manifests: Integrates with clusters.

33. Who configures Fastly WAF rules?

Security engineers configure WAF rules, defining protections for OWASP threats. They collaborate with DevOps to ensure compliance in cloud-native environments.

34. Which threats does Next-Gen WAF block?

• SQL Injection Attacks: Prevents database exploits.
• Cross-Site Scripting: Blocks script injections.
• File Inclusion Exploits: Stops unauthorized access.
• Cross-Site Request Forgery: Mitigates CSRF attacks.
• Bot-Driven Abuses: Filters automated traffic.
• Zero-Day Vulnerabilities: Uses behavioral detection.

35. How do you test WAF rule effectiveness?

Test WAF rules using penetration testing tools and simulated attacks in staging. Validate with CI/CD pipelines to ensure protection without blocking legitimate traffic in cloud-native applications.

36. What is Fastly’s role in DDoS protection?

Fastly mitigates DDoS by filtering traffic at the edge, using rate limiting and IP reputation. It ensures uptime, integrating with cloud-native architectures for automated responses.

37. Why use Fastly for API security?

Fastly secures APIs with rate limiting, WAF rules, and threat intelligence, preventing abuse. It ensures reliable delivery for microservices in cloud-native DevOps environments.

38. When should you use Fastly’s Shielding?

Use Shielding to reduce origin server load by caching at a parent server. It’s ideal for high-traffic sites, integrating with DevOps for performance optimization.

39. Where are Shielding configs defined?

• Fastly Control Center: Sets parent shielding.
• Terraform Configuration Files: Manages as code.
• Git Repositories: Tracks shielding policies.
• API Endpoint Calls: Programmatic config updates.
• CI/CD Pipeline Scripts: Automates shielding deployments.
• Kubernetes Manifests: Integrates with clusters.

40. Who optimizes shielding performance?

Performance engineers optimize shielding, tuning parent servers and caching rules. They collaborate with DevOps to ensure low-latency delivery in cloud-native media workflows.

41. Which metrics track shielding effectiveness?

• shielding_cache_hit_ratio: Measures parent cache efficiency.
• shielding_origin_requests_total: Counts origin calls.
• shielding_latency_seconds: Tracks delivery time.
• shielding_error_rate: Logs shielding failures.
• shielding_traffic_volume: Analyzes data flow.
• shielding_parent_uptime: Monitors parent availability.

42. How do you scale shielding?

Scale shielding by configuring multiple parent servers, enabling edge caching, and load-testing in staging. Monitor metrics and update via CI/CD for performance.

43. What is the impact of misconfigured shielding?

Misconfigured shielding increases origin load, slowing delivery. Tune settings, test in staging, and update via Git to ensure reliability in secure environments.

Fastly Load Balancing and Traffic

44. Why use Fastly for load balancing?

Fastly’s load balancing distributes traffic across origins, ensuring uptime and performance. It supports health checks and failover, optimizing resources in cloud-native applications.

45. When do you enable geo-steering?

Enable geo-steering to route traffic based on user location, reducing latency. It’s ideal for global applications, integrating with CI/CD for automated policy updates.

46. Where are load balancing rules defined?

• Fastly Control Center: Configures load balancers.
• Terraform Configuration Files: Manages as code.
• API Endpoint Calls: Programmatic rule updates.
• Git Repositories: Tracks rule versions.
• CI/CD Pipeline Scripts: Automates balancer configs.
• Kubernetes Manifests: Integrates with clusters.

47. Who configures load balancing policies?

Network engineers configure load balancing, setting health checks and failover rules. They align with DevOps to ensure scalability in cloud-native environments.

48. Which settings enhance load balancing?

• Health Check Intervals: Monitors server availability.
• Failover Pool Configs: Routes to backup servers.
• Geo-Steering Policies: Optimizes by location.
• Session Affinity: Maintains user sessions.
• Weighted Traffic: Balances load dynamically.
• Proximity Routing: Minimizes latency.

49. How do you debug load balancing issues?

Debug load balancing by analyzing health check logs, verifying server pools, and testing in staging. Update rules via Git and CI/CD for reliable deployments.

50. What is Fastly’s Global Traffic Management?

Global Traffic Management optimizes routing across origins, ensuring low-latency delivery. It supports high-availability applications, aligning with real-time DevOps strategies.

51. Why monitor load balancing metrics?

Monitoring load balancing metrics ensures optimal traffic distribution and uptime. It detects failover issues, aligning with DevOps for reliable cloud-native applications.

52. When do you adjust load balancing rules?

Adjust rules during traffic spikes or server failures to optimize distribution. Test in staging and deploy via CI/CD to ensure performance in workflows.

53. Where are load balancing logs stored?

• Fastly Log Delivery: Sends to SIEMs.
• External Log Aggregators: Integrates with Splunk.
• Prometheus Metrics Endpoints: Exposes traffic data.
• Grafana Dashboard Visuals: Displays real-time logs.
• Kubernetes Log Systems: Captures containerized logs.
• Cloud Logging Services: Centralizes for analysis.

54. Who optimizes load balancing performance?

Network engineers optimize load balancing, tuning health checks and weights. They monitor metrics, ensuring efficient traffic flow in cloud-native DevOps environments.

55. Which metrics track load balancing?

• load_balancer_requests_total: Counts traffic volume.
• load_balancer_latency_seconds: Measures response times.
• load_balancer_failover_events: Tracks failover triggers.
• load_balancer_healthcheck_failures: Logs server issues.
• load_balancer_traffic_by_pool: Analyzes pool distribution.
• load_balancer_geo_steering: Monitors location-based routing.

56. How do you scale load balancing?

Scale load balancing by adding server pools, tuning weights, and load-testing in staging. Monitor metrics and update via CI/CD for performance in high-traffic scenarios.

57. What is the impact of misconfigured load balancers?

Misconfigured load balancers cause uneven traffic or downtime, degrading performance. Review configs, test in staging, and update via Git for reliability in cloud-native workflows.

Fastly Video and Media Delivery

58. Why use Fastly for video delivery?

Fastly optimizes video with adaptive bitrate, edge caching, and global routing, ensuring smooth playback and reduced buffering in cloud-native media applications.

59. When do you use Adaptive Media Delivery?

Use Adaptive Media Delivery for dynamic video streaming, adjusting quality based on bandwidth. It’s ideal for live events, integrating with CI/CD for automated scaling.

60. Where are video configs defined?

• Fastly Control Center: Configures streaming behaviors.
• Terraform Configuration Files: Manages as code.
• Git Repositories: Tracks video policy versions.
• API Endpoint Calls: Programmatic config updates.
• CI/CD Pipeline Scripts: Automates video deployments.
• Kubernetes Manifests: Integrates with clusters.

61. Who optimizes video delivery?

Media engineers optimize video delivery, tuning bitrate and caching rules. They collaborate with DevOps to ensure smooth streaming in cloud-native media workflows.

62. Which metrics track video performance?

• video_bitrate_average: Measures quality levels.
• video_buffering_events: Logs buffering incidents.
• video_startup_time: Tracks initial load delays.
• video_traffic_by_quality: Analyzes resolution distribution.
• video_error_rate: Monitors playback failures.
• video_cache_hit_ratio: Tracks edge caching efficiency.

63. How do you scale video streaming?

Scale video streaming by adjusting bitrate ladders, enabling edge caching, and load-testing in staging. Monitor metrics and update via CI/CD for performance.

64. What is the impact of poor video optimization?

Poor optimization causes buffering and high abandonment rates, degrading user experience. Tune settings, test in staging, and update via Git for smooth delivery in secure DevOps.

65. Why use Fastly for live streaming?

Fastly supports live streaming with low-latency delivery, adaptive bitrate, and global edge caching. It ensures reliable broadcasts for cloud-native media applications.

66. When do you configure adaptive bitrate?

Configure adaptive bitrate for variable network conditions, ensuring smooth playback. It’s critical for live events, aligning with CI/CD for automated scaling.

67. Where are live streaming logs stored?

• Fastly Log Delivery: Sends to SIEMs.
• External Log Aggregators: Integrates with Splunk.
• Prometheus Metrics Endpoints: Exposes streaming data.
• Grafana Dashboard Visuals: Displays real-time logs.
• Kubernetes Log Systems: Captures containerized logs.
• Cloud Logging Services: Centralizes for analysis.

Fastly Troubleshooting and Best Practices

68. Why monitor Fastly metrics in production?

Monitoring metrics detects anomalies like cache misses or attack spikes, ensuring performance and security. It supports proactive resolution in DevOps configurations.

69. When should you escalate Fastly issues?

Escalate issues when metrics show persistent latency, cache misses, or security breaches. Use incident tools and CI/CD alerts for quick resolution in DevOps workflows.

70. Where are Fastly logs analyzed?

• Fastly Log Delivery: Sends to SIEMs.
• External Log Aggregators: Integrates with Splunk.
• Prometheus Metrics Endpoints: Exposes performance data.
• Grafana Dashboard Visuals: Displays real-time logs.
• Kubernetes Log Systems: Captures containerized logs.
• Cloud Logging Services: Centralizes for analysis.

71. Who troubleshoots Fastly issues?

SREs troubleshoot issues, analyzing latency and security metrics. They collaborate with DevOps to update configs via Git, ensuring optimal delivery in real-time DevOps.