What is DNS load balancing and DNS failover?
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This question targets practical, hands-on experience with Networking. Interviewers want to see if you've worked with these concepts in real projects, not just read about them. Strong answers include concrete examples.
Answer
DNS load balancing distributes traffic by returning different IP addresses in response to the same DNS query. The simplest method is Round-Robin DNS — a domain has multiple A records (different IPs) and the DNS server cycles through them. The client connects to the first IP returned. This is simple but has no health checking — if a server fails, clients still receive its IP. DNS failover monitors server health and removes failed servers' IPs from DNS responses. Advanced DNS providers (Route 53, Cloudflare, NS1) support: weighted routing (send X% to server A, Y% to server B), geolocation routing (different servers for different regions), latency-based routing (route to lowest latency endpoint), and failover routing (primary/secondary with health checks). TTL affects failover speed — short TTLs allow faster updates but increase DNS query load.
Pro Tip
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