Cache - recordcache / packetcache (hit / misses)

[vecinohk]

Hi all, please I read the documentation but I can't answer myself correctly. 👽

1. When I use dnsdist as a loadbalancer and forward requests to powerdns-recursor. Does it make sense for me to use caching on both dnsdist and recursor?
2. In powerdns-recursor I have quite successful packetcache-hits, but on the contrary cache-hits is very small. Can I please influence this somehow? I find it inefficient. There is no better recordcache.max_entries completely off (set to 0)?

cache-entries   18798
cache-hits      3149
cache-misses    30498
max-cache-entries       20000
max-packetcache-entries 10000
negcache-entries        1738
packetcache-acquired    714459
packetcache-contended   525
packetcache-entries     1553
packetcache-hits        68346
packetcache-misses      33650
record-cache-acquired   2242074
record-cache-contended  2

Thanks for the insights and sorry for the stupid questions.

[paddg]

1. When I use dnsdist as a loadbalancer and forward requests to powerdns-recursor. Does it make sense for me to use caching on both dnsdist and recursor?

Yes, because each cache relieves the load on the Recursor and dnsdist processes and thus the CPUs.

2. In powerdns-recursor I have quite successful packetcache-hits, but on the contrary cache-hits is very small. Can I please influence this somehow? I find it inefficient. There is no better recordcache.max_entries completely off (set to 0)?

The record-cache is very valuable, even if it only has a few hits (the packet cache catches a lot). Every record-cache miss leads to expensive processing.

[vecinohk]

@paddg thank you

Should I try experimenting with different values like maxTTL / minTTL or are the default values ideal?

pc = newPacketCache(10000, {maxTTL=86400, minTTL=0, temporaryFailureTTL=60, staleTTL=60, dontAge=false})
getPool(""):setCache(pc)

https://dnsdist.org/guides/cache.html

and

recursor (Does that make sense?):

packetcache:
  max_entries: 10000
  negative_ttl: 120
  servfail_ttl: 0
  shards: 256
  ttl: 86400
recordcache:
  max_cache_bogus_ttl: 14400
  max_entries: 50000
  max_negative_ttl: 7200
  max_ttl: 86400
  shards: 256

And last question. 😃
I would like to use YAML for dnsdist, but I don't know how to use this:

addAction(MaxQPSIPRule(50, 32, 64), TCAction())

local dbr = dynBlockRulesGroup()
dbr:setQueryRate(100, 20, "Exceeded query rate", 60)
dbr:setRCodeRate(DNSRCode.NXDOMAIN, 50, 20, "Exceeded NXD rate", 60)
dbr:setRCodeRate(DNSRCode.SERVFAIL, 20, 10, "Exceeded ServFail rate", 60)
dbr:setQTypeRate(DNSQType.ANY, 100, 10, "Exceeded ANY rate", 60)
dbr:setResponseByteRate(50000, 20, "Exceeded resp BW rate", 60)

function maintenance()
  dbr:apply()
end

[paddg]

Should I try experimenting with different values like maxTTL / minTTL or are the default values ideal?

In general, the default values ​​are always a good choice, you should only change them if you know exactly what you are doing and the new values ​​are confirmed by tests.

pc = newPacketCache(10000, {maxTTL=86400, minTTL=0, temporaryFailureTTL=60, staleTTL=60, dontAge=false})
getPool(""):setCache(pc)

Limiting maxTTL is a good idea. This protects you from mistakes made by third parties. minTTL=0 is default, caching records with a short lifespan doesn't do much good, but it doesn't really do any harm either. temporaryFailureTTL relieves the processes, you have to weigh up the pros and cons here. staleTTL only works in conjunction with the global configuration setStaleCacheEntriesTTL.

recursor (Does that make sense?):

As I said, use the defaults if you are not sure. I would recommend that the caches should be large enough so that they do not fill up within maxTTL.

And last question. 😃 I would like to use YAML for dnsdist, but I don't know how to use this:

I have no experience with YAML in dnsdist.

[vecinohk]

@paddg Thank you for your time. I will try more variations to see which one is best for me.