Configure optimistic cache TTL-value

[iJorgen]

Background

If a stale record is served to a client and the IP-address have changed for the record, 10 seconds feels like a really long time and could give a timeout error message. Personally I would use 1-2 seconds to get an updated record available faster to the client having connection issues. I have tried to optimize my cache-size to not store too many records, but with this settings you can use a bigger cache since in the case of a changed IP-address it's all solved in 1-2 seconds without the user noticing anything.

Solution

It would be really nice to configure the optimistic cache TTL value through the config-file instead of the hard-coded 10 seconds.

dnsproxy/proxy/cache.go

Line 108 in cff4563

const optimisticTTL = 10

Low hanging fruit?! :-)

[ameshkov]

I'd just like to avoid additional configuration when it's possible.

Are there any cases that we can reproduce when this TTL causes any troubles?

[iJorgen]

I get your point, Andrey... It's probably not a very common issue, but when using a large cache the chance of getting an old stale record not working any more if the target server/service have changed it's IP-address, is rising. Can a stale record live in the cache for days/weeks and is not deleted until the whole cache is filled up or does it respect the "cache-max-ttl" value?

I did my own Go/Make/Compiling crash-course today, so I managed to produce an executable with "optimisticTTL" adjusted to 1 second, so will evaluate if it works as I would like. :-))

All good and thanks for your ongoing improvements of DNSProxy!!

[ameshkov]

Can a stale record live in the cache for days/weeks and is not deleted until the whole cache is filled up or does it respect the "cache-max-ttl" value?

This is a good point, it can live indefinitely given that there were no requests for that domain.