Networking interview question · Most asked
How would you migrate a production domain to a new load balancer with no downtime?
Summary
Lower the DNS TTL to 60-300 s at least one old-TTL period in advance, bring up the new target, shift traffic with weighted records in steps while watching errors, keep the old target serving until its traffic reaches zero, then remove it and raise the TTL again.
Longer Answer
Account for client-side caches (JVM DNS cache, long-lived connection pools) and negative caching of mistakes. Make sure TLS certificates and health checks are ready on the new target before shifting any traffic.
Key Points
- Lower TTL in advance.
- Weighted shift with monitoring.
- Keep the old target until idle.
- Watch client caches.
Deep dive: Cloud Networking in Production: The Migration That Took Two Days
Explanation
What interviewers look for
A staged plan with verification at each step.
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