Caching successful DNS in modern Java

Things have moved on a bit since I set up a custom DNS resolver for microservices to enable them to continue to use known successfully resolved addresses when DNS resolution subsequently fails.

Since Java 22 we can specify a value in a file in the JDK to have the option of continuing to use successful lookup results even after the TTL expires.

The property name is:

networkaddress.cache.stale.ttl

https://bugs.openjdk.org/browse/JDK-8306653

A trade-off to consider when applying that approach instead of a customised DNS Resolver is that we would not have the option of detecting when normal DNS resolution has failed.

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