Question about DNS Caching

[Dynamic5912]

I have a question about how DNS Caching works with AGH.

• If I enable the Cache (i.e. specify a Cache Size) - what happens when items expire - are they retained or deleted from the cache?

• If I enable Optimistic Caching - does this mean items are cached indefinitely (retained forever?) even after expiration and then served and refreshed in the background (i.e. like Unbound's serve-expired setting)?

On the Configuration Page I see a reference to this:

cache_time: Time interval in minutes for keeping cache records.

And in the YAML file it's set to "30" - does this mean cached items are only retained for 30 minutes?

Does this get reset each time they are called from the cache and updated?

[schzhn]

Cached responses are retained indefinitely until they are replaced by new responses. This depends on the size of the cache (dns.cache_size) and the number of stored responses.

If you enable the "Optimistic Caching" setting (dns.cache_optimistic), expired responses are still provided with a Time-To-Live (TTL) of 10. In the background, AdGuard Home queries the upstream server and updates the cached response, so subsequent requests receive the updated response.
See https://github.com/AdguardTeam/dnsproxy/blob/129cf05264e1945ccbb2d1b9f8a5fe62522965d3/proxy/cache.go#L115

The "filtering.cache_time" setting defines how long hashes, used for safe browsing and parental control, are stored.

[Dynamic5912]

Cached responses are retained indefinitely until they are replaced by new responses. This depends on the size of the cache (dns.cache_size) and the number of stored responses.

If you enable the "Optimistic Caching" setting (dns.cache_optimistic), expired responses are still provided with a Time-To-Live (TTL) of 10. In the background, AdGuard Home queries the upstream server and updates the cached response, so subsequent requests receive the updated response.

See https://github.com/AdguardTeam/dnsproxy/blob/129cf05264e1945ccbb2d1b9f8a5fe62522965d3/proxy/cache.go#L115

The "filtering.cache_time" setting defines how long hashes, used for safe browsing and parental control, are stored.

Thanks.

So when a cached record expires (I.e the TTL runs out) it's still retained in the cache and served to clients?

Or is it deleted and replaced with the updated record when a request is made?

I understand optimising caching does this in the background when enabled - but if it's not enabled how do cached records behave?

[schzhn]

In the cache, AdGuardHome stores the last N responses. When it receives a request, it checks the cache to see if there is a non-expired response available. If so, it serves that response. Otherwise, it queries the upstream server, serves the response from the upstream, and updates the cache.

If optimistic caching is enabled, AdGuardHome serves an expired response with a short TTL and updates the cache in the background.