Most Asked Fastly Interview Questions [2025 Updated]

Core Fastly Concepts

1. What is Fastly’s primary role in edge computing?

Fastly’s edge platform delivers low-latency content via a global CDN, using VCL for custom logic. It supports real-time request handling, caching, and security. Logs monitor performance, CI/CD automates updates, and DevSecOps ensures scalable, secure operations for dynamic applications. Learn incident management.

2. How does Fastly’s VCL enable edge customization?

Varnish Configuration Language (VCL) allows custom request/response logic at the edge, enabling dynamic caching, header manipulation, and routing. Logs track VCL executions, CI/CD automates deployments, and DevSecOps ensures secure, scalable edge logic, enhancing real-time performance for global applications.

3. When is Fastly’s Next-Gen WAF used?

Fastly’s Next-Gen WAF is used for real-time threat detection in dynamic apps, leveraging ML to block OWASP Top 10 attacks. Logs monitor threats, CI/CD updates rules, and DevSecOps ensures secure, low-latency protection without performance degradation.

4. Where does Fastly deploy its edge nodes?

• Over 100 POPs in 90+ countries near ISPs.
• Peering with cloud providers for efficiency.
• Logs node metrics for real-time monitoring.
• CI/CD automates node configuration updates.
• DevSecOps ensures secure deployments.
• Supports global low-latency delivery.
• Enhances real-time availability.

5. Who manages Fastly’s VCL configurations?

DevOps engineers write and deploy VCL, SREs monitor performance, and security teams ensure compliance. Logs track changes, CI/CD automates updates, and DevSecOps principles guarantee secure, scalable configurations, enabling reliable edge logic for production environments.

6. Which Fastly services enhance security?

• Next-Gen WAF for ML-based threat detection.
• Rate Limiting to prevent DDoS attacks.
• Bot Management for automated bot mitigation.
• Logs security events for auditing.
• Integrates with Sysdig monitoring.
• DevSecOps ensures scalable security.
• Protects dynamic applications.

7. How does Fastly mitigate DDoS attacks?

Fastly mitigates DDoS attacks using Rate Limiting, Next-Gen WAF, and traffic scrubbing. Logs track attack patterns, CI/CD updates rules, and VCL customizes responses. DevSecOps ensures resilient, low-latency defense, maintaining application availability during volumetric or application-layer attacks.

Explore PagerDuty integration for incident response.

8. What is Fastly’s approach to real-time edge computing?

• EdgeWorkers for serverless JavaScript execution.
• VCL for custom real-time logic.
• Logs execution metrics for monitoring.
• CI/CD automates code deployments.
• DevSecOps ensures secure execution.
• Reduces latency for dynamic apps.
• Supports real-time DevOps workflows.

VCL and Edge Logic Questions

9. How do you write a VCL subrequest for dynamic content?

Write VCL subrequests in sub vcl_sub, passing headers for dynamic content processing. Use set status for responses, log results, and test with curl. CI/CD automates deployments, aligning with DevSecOps for secure, scalable edge logic, ensuring low-latency dynamic content delivery.

10. Why do VCL errors cause edge failures?

• Syntax errors prevent VCL compilation.
• Misconfigured subrequests cause loops.
• Log errors for debugging.
• CI/CD validates VCL before deployment.
• Test with simulated requests.
• DevSecOps ensures reliable execution.
• Prevents edge processing failures.

11. What is VCL’s role in Fastly’s platform?

VCL enables custom edge logic for request/response handling, caching, and security. It compiles to C for high performance, logs executions, and CI/CD automates updates. DevSecOps ensures secure, scalable VCL, supporting real-time customization for dynamic applications at the edge.

12. How do you debug a VCL compilation error?

• Use Fastly CLI to validate VCL syntax.
• Run vcl lint for error detection.
• Log compilation errors for analysis.
• CI/CD automates VCL testing.
• Test with simulated edge requests.
• Align with DevSecOps for secure debugging.
• Resolve errors efficiently.

13. Where do you define VCL custom variables?

Define VCL custom variables in vcl_init using set req.http.var_name for request handling. Use in vcl_recv or vcl_deliver, log values, and test with curl. CI/CD automates deployments, aligning with DevSecOps for scalable, secure edge logic customization.

14. Who manages VCL deployments in Fastly?

DevOps engineers deploy VCL via Fastly CLI and CI/CD pipelines. SREs monitor performance, and security teams ensure compliance. Logs track changes, aligning with DevSecOps for secure, reliable edge logic management, ensuring seamless operation of dynamic applications.

15. Which VCL subroutines handle requests?

• vcl_recv processes incoming requests.
• vcl_hash determines caching keys.
• vcl_backend_fetch handles origin requests.
• Log subroutine executions for analysis.
• CI/CD tests VCL logic.
• Align with Spacelift CI/CD.
• Ensure efficient request handling.

Discover Spacelift automation for VCL.

Security and WAF Questions

16. How does Fastly’s Next-Gen WAF protect applications?

Next-Gen WAF uses machine learning for real-time threat detection, blocking OWASP Top 10 attacks like SQL injection. Logs monitor threats, CI/CD updates rules, and VCL customizes responses. DevSecOps ensures secure, low-latency protection, safeguarding dynamic applications without compromising performance.

17. Why do WAF false positives occur in Fastly?

• Broad rule expressions misidentify legitimate traffic.
• Misconfigured ML models cause errors.
• Log false positives for analysis.
• CI/CD tests rule updates.
• Tune thresholds for accuracy.
• DevSecOps ensures reliable WAF.
• Minimizes application disruptions.

18. What is Fastly’s Rate Limiting feature?

Rate Limiting controls request volumes to prevent DDoS and abuse, configurable via VCL or dashboard. Logs track limited requests, CI/CD automates updates, and DevSecOps ensures secure, scalable protection, maintaining API and application availability under high traffic conditions.

19. How do you configure Bot Management in Fastly?

• Enable Bot Management in dashboard.
• Use ML for bot behavior scoring.
• Log bot activity for auditing.
• CI/CD automates rule updates.
• Test with simulated bot traffic.
• DevSecOps ensures secure detection.
• Blocks malicious bots effectively.

20. Where do you monitor WAF threats in Fastly?

Monitor WAF threats in Fastly’s dashboard, Prometheus for metrics, and Grafana for visualization. Logs capture rule hits, CI/CD validates monitoring, and DevSecOps ensures observable, secure operations, enabling rapid threat detection and response for production applications.

21. Who manages WAF rule updates?

Security engineers update WAF rules, SREs monitor threats, and DevOps automate via CI/CD. Logs track rule changes, aligning with DevSecOps for secure, scalable configurations, ensuring robust protection against evolving threats while maintaining application performance.

22. How do you troubleshoot WAF false positives?

Troubleshoot WAF false positives by reviewing rule expressions, whitelisting trusted IPs, and logging blocked requests. Test with safe traffic, update via CI/CD, and align with DevSecOps to ensure accurate, secure WAF operations, minimizing disruptions to legitimate users.

Explore cloud security scenarios for WAF.

Edge Computing Questions

23. What are Fastly EdgeWorkers?

EdgeWorkers execute serverless JavaScript at the edge for custom logic, reducing latency for dynamic content. Deploy via CLI, log executions, and automate with CI/CD. DevSecOps ensures secure, scalable edge computing, supporting real-time applications with low-latency processing.

24. How do you deploy EdgeWorkers in Fastly?

• Develop JavaScript using Fastly CLI.
• Deploy to edge via CI/CD pipelines.
• Log execution metrics for monitoring.
• Test in development environment.
• Validate routes with API tests.
• DevSecOps ensures secure deployments.
• Supports scalable edge execution.

25. Why do EdgeWorkers fail to execute?

EdgeWorkers fail due to syntax errors, resource limits, or logic issues. Validate code with CLI, log errors, and test in development. CI/CD ensures reliable deployments, while DevSecOps aligns for secure, low-latency execution, preventing disruptions in edge applications.

26. Where do you store state for EdgeWorkers?

Store state in Fastly’s KV Store for key-value data at the edge. Log storage operations, validate with CI/CD, and test with simulated data. DevSecOps ensures stateful, scalable edge applications, enabling efficient data management for dynamic, low-latency workloads.

27. Who manages EdgeWorker deployments?

DevOps engineers deploy EdgeWorkers via CLI and CI/CD, SREs monitor performance, and security teams ensure compliance. Logs track deployments, aligning with DevSecOps for secure, reliable management of serverless edge logic, ensuring seamless operation for dynamic applications.

28. Which limits affect Fastly EdgeWorkers?

• CPU time limits per execution.
• Memory constraints for scripts.
• Log metrics for performance analysis.
• CI/CD optimizes code efficiency.
• Test in development for compliance.
• DevSecOps ensures scalability.
• Ensures reliable edge performance.

29. How do you optimize EdgeWorkers for performance?

Optimize EdgeWorkers by minimizing subrequests, using KV Store caching, and logging execution times. Test with CLI, automate via CI/CD, and simulate workloads. DevSecOps ensures low-latency, scalable edge computing, enhancing performance for real-time applications with dynamic content. Learn cloud security.

System Design Questions

30. How do you design a scalable Fastly CDN system?

Design a CDN with Anycast routing, VCL for custom logic, and edge caching for scalability. Log performance metrics, automate configs via CI/CD, and test with simulated traffic. DevSecOps ensures low-latency, reliable content delivery for global, high-traffic applications.

31. What is the system design for Fastly’s Zero Trust?

• Next-Gen WAF for identity-based access control.
• Rate Limiting for secure traffic filtering.
• Log access events for auditing.
• CI/CD automates policy updates.
• Test with simulated user access.
• DevSecOps ensures secure design.
• Protects enterprise applications.

32. How do you architect a DDoS mitigation system?

Architect DDoS mitigation with Rate Limiting, Next-Gen WAF, and traffic scrubbing. Log attack patterns, update defenses via CI/CD, and test with simulated attacks. DevSecOps ensures resilient, scalable protection, maintaining application availability during volumetric and application-layer attacks.

33. Why design a load balancer for Fastly?

A load balancer distributes traffic using health checks and geo-steering, ensuring high availability. Logs monitor balancing, CI/CD automates configs, and DevSecOps prevents single points of failure, optimizing traffic flow and ensuring reliable content delivery for global applications.

34. How do you design a low-latency DNS resolver?

• Use Anycast for proximity-based routing.
• Enable DNSSEC for secure resolutions.
• Log queries for performance analysis.
• CI/CD automates DNS updates.
• Test with dig for resolution speed.
• DevSecOps ensures reliable DNS.
• Delivers fast, secure resolutions.

35. What is the architecture for Fastly EdgeWorkers?

EdgeWorkers use V8 isolates for serverless execution, with KV Store for state management. Logs track performance, CI/CD automates deployments, and DevSecOps ensures scalable, low-latency edge computing, supporting dynamic content processing for real-time applications.

36. How do you design a secure WAF system?

• Use Next-Gen WAF managed rules for threats.
• Add custom rules for specific vulnerabilities.
• Log rule hits for analysis.
• CI/CD automates rule updates.
• Test with simulated attack traffic.
• DevSecOps ensures secure WAF.
• Protects applications effectively.

Understand cloud security engineering for WAF design.

Troubleshooting Questions

37. What causes a CDN outage in Fastly?

CDN outages stem from VCL syntax errors, cache misconfigurations, or origin failures. Validate VCL with CLI, log cache misses, and test origins with API. CI/CD automates updates, while DevSecOps ensures rapid recovery, restoring reliable content delivery across edge servers.

38. How do you troubleshoot a DNS failure?

• Validate records with dig or nslookup.
• Check zone configs in dashboard.
• Log resolution errors for analysis.
• CI/CD automates DNS testing.
• Test failover with API simulations.
• DevSecOps ensures reliable DNS.
• Resolves outages quickly.

39. Why does a WAF rule cause downtime?

WAF rules cause downtime by blocking legitimate traffic due to overly broad expressions. Review rules, whitelist IPs, and log blocked requests. CI/CD automates testing, while DevSecOps ensures accurate configurations, minimizing disruptions and maintaining secure, reliable application access.

40. How do you debug an EdgeWorker failure?

Debug EdgeWorker failures by analyzing logs for syntax or resource errors, validating code with Fastly CLI, and testing in development. CI/CD automates updates, aligning with DevSecOps to ensure reliable, low-latency execution, quickly restoring edge application functionality.

41. What causes a Zero Trust policy failure?

• Misconfigured Next-Gen WAF or rate limits.
• Log authentication failures for analysis.
• Validate policies with API tests.
• CI/CD automates policy updates.
• Test with simulated user access.
• DevSecOps ensures secure policies.
• Ensures reliable authentication.

42. Where do you monitor performance issues?

Monitor performance in Fastly’s dashboard, Prometheus for metrics, and Grafana for visualization. Log latency and errors, validate with CI/CD, and align with DevSecOps for observable operations, enabling rapid detection and resolution of issues in production environments.

43. Who handles DDoS mitigation in Fastly?

SREs configure Rate Limiting and WAF rules, security engineers update defenses, and DevOps automate via CI/CD. Logs track attacks, aligning with DevSecOps for resilient mitigation, ensuring application availability during attacks. Learn cloud security.

Coding and Implementation Questions

44. How do you implement a rate limiter in Fastly?

Implement a rate limiter in VCL using subrequests to track request counts, storing counters in variables. Log limit events, test with curl, and automate via CI/CD. DevSecOps ensures scalable, secure protection against DDoS and abuse, maintaining application availability.

45. What is the complexity of Fastly’s DNS lookup?

• Uses trie for O(log n) prefix matching.
• Anycast routing optimizes resolution speed.
• Logs lookup times for analysis.
• CI/CD automates code testing.
• Test with simulated DNS queries.
• DevSecOps ensures efficient DNS.
• Delivers fast resolutions.

46. How do you code an EdgeWorker for API routing?

• Use JavaScript for dynamic routing logic.
• Define routes in Fastly CLI.
• Log routing decisions for analysis.
• CI/CD automates deployments.
• Test in development environment.
• DevSecOps ensures secure routing.
• Ensures low-latency API performance.

47. Why use Golang for Fastly’s backend systems?

Golang’s goroutines provide high-throughput, low-memory networking, ideal for Fastly’s backend. Logs monitor performance, CI/CD automates deployments, and DevSecOps ensures reliable, secure operations, supporting scalable edge platforms for real-time content delivery and security services.

48. How do you implement an LRU cache for CDN?

Implement an LRU cache in Golang using a hash map and doubly linked list for O(1) access. Log cache operations, test with CI/CD, and align with DevSecOps for efficient, scalable caching, reducing latency and enhancing CDN performance for high-traffic applications.

49. What is the approach to coding a DDoS detector?

• Use anomaly detection for traffic patterns.
• Implement in Golang with Prometheus metrics.
• Log suspicious traffic for analysis.
• CI/CD validates detection models.
• Test with simulated attack datasets.
• DevSecOps ensures secure detection.
• Enhances proactive mitigation.

50. How do you code a consistent hash ring for load balancing?

Code a consistent hash ring in Golang with virtual nodes for balanced traffic distribution. Log hash operations, test with CI/CD, and align with DevSecOps for scalable, reliable load balancing, ensuring optimal performance in Fastly’s edge platform.

Explore SRE FAQs for coding prep.

Production Questions

51. What causes a production CDN outage?

Production CDN outages result from VCL errors, cache misconfigurations, or origin failures. Validate VCL with CLI, log cache misses, and test origins with API. CI/CD automates updates, while DevSecOps ensures rapid recovery, restoring reliable content delivery across edge servers.

52. How do you troubleshoot a production DNS failure?

• Validate records with dig or nslookup.
• Check zone configs in dashboard.
• Log resolution errors for analysis.
• CI/CD automates DNS testing.
• Test failover with API simulations.
• DevSecOps ensures reliable DNS.
• Resolves outages quickly.

53. Why does a WAF rule cause downtime?

WAF rules cause downtime by blocking legitimate traffic due to broad expressions or false positives. Review rules, whitelist IPs, and log blocked requests. CI/CD automates testing, while DevSecOps ensures accurate configurations, minimizing disruptions and maintaining secure application access.

54. How do you debug an EdgeWorker failure?

Debug EdgeWorker failures by analyzing logs for syntax or resource errors, validating code with Fastly CLI, and testing in development. CI/CD automates updates, aligning with DevSecOps to ensure reliable, low-latency execution, quickly restoring edge application functionality.

55. What causes a Zero Trust policy failure?

• Misconfigured Next-Gen WAF or rate limits.
• Log authentication failures for analysis.
• Validate policies with API tests.
• CI/CD automates policy updates.
• Test with simulated user access.
• DevSecOps ensures secure policies.
• Ensures reliable authentication.

56. Where do you monitor production performance issues?

Monitor performance in Fastly’s dashboard, Prometheus for metrics, and Grafana for visualization. Log latency, cache hits, and errors, while CI/CD validates monitoring. DevSecOps ensures observability, enabling rapid issue detection and resolution for reliable production operations.

57. Who handles DDoS mitigation in production?

SREs configure Rate Limiting and WAF rules, security engineers update defenses, and DevOps automate via CI/CD. Logs track attacks, aligning with DevSecOps for resilient mitigation, ensuring application availability during attacks. Learn cloud security.

Advanced Questions

58. How do you optimize VCL for high-traffic applications?

Optimize VCL by minimizing subrequests, using efficient caching, and logging performance metrics. Test with Fastly CLI, automate via CI/CD, and simulate high traffic. DevSecOps ensures low-latency, scalable edge logic, enhancing performance for high-traffic applications with dynamic content.

59. What causes high latency in Fastly’s CDN?

High latency results from cache misses, suboptimal routing, or slow origins. Validate VCL, log performance metrics, and optimize with shielding. CI/CD automates updates, while DevSecOps ensures low-latency delivery, improving user experience across Fastly’s global edge network.

60. How do you configure real-time logging in Fastly?

• Define log endpoints in dashboard or VCL.
• Stream to syslog or cloud providers.
• Log request/response metrics for analysis.
• CI/CD automates logging configs.
• Test with simulated traffic.
• DevSecOps ensures secure logging.
• Enables real-time observability.

61. Why does a VCL subrequest loop occur?

VCL subrequest loops occur due to recursive calls or misconfigured conditions. Validate logic with Fastly CLI, log subrequest executions, and test in development. CI/CD ensures error-free deployments, while DevSecOps prevents loops, maintaining reliable edge processing for production applications.

62. How do you implement shielding in Fastly?

Implement shielding by designating a POP as the primary origin cache, reducing origin load. Configure in VCL, log shielding metrics, and test with CI/CD. DevSecOps ensures scalable, low-latency caching, improving CDN performance for high-traffic applications.

63. What is the role of Fastly’s API in automation?

Fastly’s API automates VCL deployments, cache purges, and configuration updates. Logs track API calls, CI/CD integrates for automation, and DevSecOps ensures secure, scalable operations, enabling real-time management of edge services for dynamic, high-availability applications.

64. How do you handle a production VCL rollback?

Rollback VCL by reverting to a previous version via Fastly dashboard or API. Log rollback events, test in staging with CI/CD, and align with DevSecOps to ensure rapid recovery, minimizing downtime and restoring reliable edge logic in production.

Learn GitLab CI/CD for automation.

Advanced Coding Questions

65. How do you implement a token bucket rate limiter?

Implement a token bucket rate limiter in Golang using Redis for distributed state to manage request bursts. Log limit events, test with simulated traffic via CI/CD, and align with DevSecOps for secure, scalable DDoS protection, ensuring application availability.

66. What is the complexity of Fastly’s BGP routing?

• Uses trie for O(log n) prefix matching.
• BGP announcements optimize routing efficiency.
• Logs route lookups for analysis.
• CI/CD automates code testing.
• Test with simulated BGP routes.
• DevSecOps ensures efficient routing.
• Delivers fast traffic handling.

67. How do you code an EdgeWorker for caching?

Code an EdgeWorker in JavaScript using KV Store for state and Cache API for responses. Log cache operations, test with CI/CD, and align with DevSecOps for efficient, scalable caching, reducing latency and enhancing CDN performance for dynamic applications.

68. How do you optimize EdgeWorkers for low latency?

Optimize EdgeWorkers by minimizing subrequests, using KV Store caching, and logging execution times. Test with Fastly CLI, automate via CI/CD, and simulate workloads. DevSecOps ensures low-latency, scalable edge computing for real-time applications with dynamic content.

69. What is the approach to coding a traffic anomaly detector?

• Use statistical models for anomaly detection.
• Implement in Golang with Prometheus metrics.
• Log anomalies for real-time analysis.
• CI/CD validates detection models.
• Test with simulated attack datasets.
• DevSecOps ensures secure detection.
• Enhances proactive mitigation.

Learn GitLab CI/CD for automation.

Advanced Production Questions

70. What causes high latency in a production app?

High latency stems from cache misses, suboptimal routing, or slow origins. Optimize with shielding, validate VCL, and log performance metrics. CI/CD automates updates, while DevSecOps ensures low-latency delivery, improving user experience and maintaining reliable content delivery.

71. How do you mitigate a production DDoS attack?

• Enable Rate Limiting and WAF rules.
• Configure traffic scrubbing in dashboard.
• Log attack patterns for analysis.
• CI/CD updates defense configs.
• Monitor with Prometheus metrics.
• DevSecOps ensures resilient mitigation.
• Minimizes production downtime.

72. Why does an EdgeWorker exceed resource limits?

EdgeWorkers exceed limits due to complex logic or excessive subrequests. Optimize with Fastly CLI, use KV Store caching, and log execution times. Test in development, update via CI/CD, and align with DevSecOps for reliable, low-latency edge performance in production.

73. How do you troubleshoot a WAF false positive?

Troubleshoot WAF false positives by reviewing rule expressions, whitelisting IPs, and logging blocked requests. Test with safe traffic, update via CI/CD, and align with DevSecOps for accurate threat detection, minimizing disruptions and ensuring secure application access.

74. What causes DNS propagation delays?

• Misconfigured TTLs or zone settings.
• Log propagation delays for analysis.
• Validate records with dig queries.
• CI/CD automates DNS updates.
• Test with API-based simulations.
• DevSecOps ensures reliable DNS.
• Ensures fast propagation.

75. How do you manage a load balancer failure?

Manage load balancer failures by validating health checks, logging failover events, and testing with API simulations. Update configs via CI/CD, aligning with DevSecOps to restore reliable traffic distribution, minimizing downtime and ensuring high availability for applications.

76. Where do you monitor real-time production metrics?

Monitor real-time metrics in Fastly’s dashboard, Prometheus for scrape jobs, and Grafana for visualization. Log issues, validate with CI/CD, and align with DevSecOps for observability, enabling rapid issue detection and resolution. Explore ArgoCD.

Interview Preparation Questions

77. What should you study for a Fastly DevOps interview?

Study VCL, EdgeWorkers, Next-Gen WAF, CDN, and Zero Trust. Practice with Fastly CLI, simulate API scenarios, and learn Prometheus monitoring. Master CI/CD and DevSecOps principles for scalable, secure edge operations, ensuring readiness for complex DevOps interview scenarios.

78. How do you optimize a production app’s CDN performance?

Optimize CDN performance with shielding, efficient VCL caching, and Anycast routing. Log latency metrics, test with CI/CD, and simulate high traffic. DevSecOps ensures low-latency, scalable delivery, enhancing user experience and maintaining reliable content delivery across edge servers.

79. Why does a VCL configuration fail in production?

VCL configurations fail due to syntax errors, logic loops, or incompatible rules. Validate with Fastly CLI, log errors, and test in staging. CI/CD ensures error-free deployments, while DevSecOps prevents failures, maintaining reliable edge logic for production applications.

80. How do you configure real-time DDoS mitigation?

• Enable Rate Limiting for traffic control.
• Configure Next-Gen WAF for app-layer protection.
• Log attack patterns for analysis.
• CI/CD automates defense updates.
• Test with simulated attack traffic.
• DevSecOps ensures resilient mitigation.
• Protects apps effectively.

81. How do you debug an EdgeWorker failure?

Debug EdgeWorker failures by analyzing logs for errors, validating code with Fastly CLI, and testing in development. CI/CD automates updates, aligning with DevSecOps to ensure reliable, low-latency execution, quickly restoring functionality for edge-based applications in production.

82. How do you troubleshoot a production DNS issue?

Troubleshoot DNS issues by validating records with dig, checking zone configs, and logging errors. Automate testing with CI/CD, test failover with API simulations, and align with DevSecOps to ensure rapid resolution, minimizing downtime and maintaining reliable DNS performance.

83. What causes a Zero Trust failure?

• Misconfigured WAF or rate limiting rules.
• Log authentication failures for analysis.
• Validate policies with API tests.
• CI/CD automates policy updates.
• Test with simulated user access.
• DevSecOps ensures secure policies.
• Restores reliable authentication.

84. Where do you test Fastly configurations?

Test configurations in staging using Fastly API, CLI for EdgeWorkers, and dashboard for VCL/WAF. Log errors, automate testing with CI/CD, and align with DevSecOps to ensure reliable, secure configurations, preventing production issues and maintaining consistent performance.

85. Who manages WAF issues in production?

Security engineers manage WAF issues by validating rules and whitelisting IPs. SREs monitor logs, DevOps automate via CI/CD, and logs track performance. DevSecOps ensures secure, accurate operations, minimizing disruptions and maintaining reliable application protection in production.

86. How do you code a rate limiter for Fastly apps?

• Implement token bucket in VCL.
• Use variables for request counters.
• Log rate limit events for analysis.
• CI/CD automates code testing.
• Test with simulated request bursts.
• DevSecOps ensures secure limiting.
• Protects apps from DDoS.

87. What causes a load balancer failure?

Load balancer failures result from misconfigured health checks, failover issues, or routing errors. Validate configs, log failover events, and test with API simulations. CI/CD automates updates, while DevSecOps ensures reliable traffic distribution, restoring high availability and minimizing downtime.

88. How do you optimize EdgeWorkers for real-time apps?

Optimize EdgeWorkers by minimizing subrequests, using KV Store caching, and logging execution times. Test with Fastly CLI, automate via CI/CD, and simulate workloads. DevSecOps ensures low-latency, scalable edge computing for real-time applications. Learn ELK for logging.

89. How do you simulate a DDoS attack for testing?

Simulate a DDoS attack using Locust to generate high traffic against Fastly endpoints. Log attack patterns, validate WAF rules, and test via CI/CD. DevSecOps ensures robust defense validation, confirming effective mitigation and maintaining application availability under attack conditions.

Additional Fastly-Specific Questions

90. How do you configure Fastly’s Instant Purge?

Configure Instant Purge via Fastly API or dashboard to invalidate cache by URL or surrogate key. Log purge events, test with CI/CD, and align with DevSecOps for secure, rapid content updates, ensuring fresh content delivery with minimal latency in production.

91. What is Fastly’s shielding feature?

Shielding designates a POP as the primary cache to reduce origin load, improving performance. Configure in VCL, log metrics, and test with CI/CD. DevSecOps ensures scalable, low-latency caching, enhancing CDN efficiency for high-traffic applications in production environments.

92. Why use Fastly’s real-time logging?

Real-time logging streams request/response data to syslog or cloud providers, enabling immediate performance and security insights. Configure in VCL, validate with CI/CD, and align with DevSecOps for observable operations, supporting rapid issue detection and resolution in production.

93. How do you implement geo-steering in Fastly?

Implement geo-steering in VCL using client.geo variables to route traffic based on location. Log routing decisions, test with CI/CD, and align with DevSecOps for low-latency, region-specific delivery, optimizing user experience for global applications.

94. What causes cache misses in Fastly?

• Short TTLs or uncacheable content.
• Misconfigured VCL cache rules.
• Log cache misses for analysis.
• CI/CD validates cache settings.
• Test with simulated traffic.
• DevSecOps optimizes cache hits.
• Improves CDN performance.

95. How do you configure TLS in Fastly?

Configure TLS with Fastly’s automated certificate management for secure HTTPS. Log certificate renewals, automate via CI/CD, and test with API checks. DevSecOps ensures encrypted, reliable traffic delivery, maintaining security and performance for production applications.

96. Why does a VCL update fail in production?

VCL updates fail due to syntax errors, incompatible logic, or deployment issues. Validate with Fastly CLI, log errors, and test in staging. CI/CD ensures error-free updates, while DevSecOps prevents failures, maintaining reliable edge logic for production applications.

97. How do you monitor Fastly’s cache hit ratio?

Monitor cache hit ratio in Fastly’s dashboard, Prometheus for metrics, and Grafana for visualization. Log cache hits/misses, validate with CI/CD, and align with DevSecOps for observability, optimizing CDN performance and reducing latency in production environments.

98. Who manages Fastly’s TLS certificates?

DevOps engineers manage TLS certificates via Fastly’s API, SREs monitor renewals, and security teams ensure compliance. Logs track certificate events, CI/CD automates renewals, and DevSecOps ensures secure, reliable HTTPS delivery for production applications.

99. What is Fastly’s approach to API rate limiting?

• Implement rate limits in VCL.
• Use variables for request tracking.
• Log limit events for analysis.
• CI/CD automates rule testing.
• Test with simulated API traffic.
• DevSecOps ensures secure APIs.
• Protects against abuse.

100. How do you implement a failover in Fastly?

Implement failover by configuring backup origins in VCL with health checks. Log failover events, test with CI/CD, and align with DevSecOps for reliable, high-availability routing, ensuring uninterrupted content delivery during origin failures in production environments.

101. How do you test Fastly configurations?

Test configurations in staging using Fastly API, CLI for EdgeWorkers, and dashboard for VCL/WAF. Log errors, automate testing with CI/CD, and align with DevSecOps to ensure reliable, secure configurations, preventing issues and maintaining performance in production.

Learn ArgoCD automation for testing.