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We run a latency-sensitive system. We found one significant cause of latency: some processes were making blocking DNS lookups to remote nameservers. To mitigate this, we have installed a local caching DNS resolver, specially dnsmasq.

But we still see occasional significant pauses where queries to the local DNS cache (dnsmasq) can take a long time. These are caused by TTL expiry; in these cases dnsmasq queries its upstream server before responding to the local process.

We would like to eliminate these pauses, too. I would like our local DNS cache to always respond immediately, even if the response is stale. The cache should query its upstream server asynchronously. For example, if the cache serves a stale response, it could refresh this asynchronously. Or a more sophisticated policy would be to refresh the cache asynchronously shortly before the TTL expires.

But I can't find any such setting for dnsmasq, or for any other caching DNS servers I've looked at. Are any DNS servers designed to run in this configuration?

jameshfisher
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2 Answers2

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Knot resolver with configuration modules = { 'predict' } will start asynchronous refresh of records that are put into answer at a moment when their TTL is close to expiration.

Note that version 2.0.0 has a bug that defeats this refresh for records without DNSSEC signatures (will be fixed in the next release).

Vladimír Čunát
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Unbound DNS Server also does this with a prefetch option - yes/no.

vnandi
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