Using DNS to Gracefully Switch Network Services

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Assume the service domain name is example.domain, the original server IP is A, and the new server IP is B after migration or IP change. To keep users unaware, we can use DNS to gracefully switch network services.

  1. Original state: example.domain resolves to IP A.
  2. Transition state: example.domain resolves to both IP A and B.
  3. New state: example.domain resolves to IP B; IP A is removed.

Note: When users receive two resolved addresses, the client picks one to connect to; if that fails, it tries the others, ensuring service availability.

Since DNS responses are cached, the transition state must last long enough for all caches to expire.

I’m migrating a DNS service, so I can accelerate the switch by adding “DNS rewrites” during the transition.

Rewrite rules for server A:

Server A rewrite

Rewrite rules for server B:

Server B rewrite

The expanded migration steps are:

  1. Original state: example.domain resolves to IP A.
  2. Transition state: in DNS A, example.domain is rewritten to A and B; in DNS B, it is rewritten to B.
  3. New state: example.domain resolves to IP B; IP A is removed.

Clients still querying DNS A receive both addresses.

  • With 50 % probability they pick DNS A.
  • With 50 % probability they switch to DNS B.
    • If DNS B fails, they fall back to DNS A.
    • If DNS B is healthy, they see only B and stay on DNS B.

This gradually reduces load on DNS A without abruptly terminating it, achieving a smoother migration.