Add DNS Cache that respects TTL of resolved DNS records #28
Description
Problem
When DNS over HTTPS resolver is set up, every query produces HTTP request.
To illustrate, when using https://resolver.cloudflare-eth.com/dns-query for crypto TLDs, this adds around 1 second to EVERY resolution event (only the very first one should be that slow):
$ t ipfs name resolve /ipns/brave.crypto
/ipfs/QmWrdNJWMbvRxxzLhojVKaBDswS4KNVM7LvjsN7QbDrvka
0.25s user 0.03s system 21% cpu 1.274 total
$ t ipfs name resolve /ipns/brave.crypto /ipfs/QmWrdNJWMbvRxxzLhojVKaBDswS4KNVM7LvjsN7QbDrvka
0.21s user 0.02s system 20% cpu 1.100 total
$ t ipfs name resolve /ipns/brave.crypto
/ipfs/QmWrdNJWMbvRxxzLhojVKaBDswS4KNVM7LvjsN7QbDrvka
0.23s user 0.02s system 23% cpu 1.058 totalTo illustrate, using non-DoH name leverages OS-level resolver as a cache, and only first lookup is expensive:
$ t ipfs name resolve /ipns/en.wikipedia-on-ipfs.org
/ipfs/bafybeiaysi4s6lnjev27ln5icwm6tueaw2vdykrtjkwiphwekaywqhcjze
0.23s user 0.05s system 80% cpu 0.343 total
$ t ipfs name resolve /ipns/en.wikipedia-on-ipfs.org /ipfs/bafybeiaysi4s6lnjev27ln5icwm6tueaw2vdykrtjkwiphwekaywqhcjze
0.04s user 0.01s system 173% cpu 0.029 total
$ t ipfs name resolve /ipns/en.wikipedia-on-ipfs.org /ipfs/bafybeiaysi4s6lnjev27ln5icwm6tueaw2vdykrtjkwiphwekaywqhcjze
0.03s user 0.02s system 160% cpu 0.032 totalSolution
The problem is not limited to DoH – there is no point in hitting OS-level default resolver if we could use cached record.
We need to add a global DNS Cache to resolve.go that makes sure we don't do redundant lookups until TTL from resolved record expires.
cc @aschmahmann @vyzo what would be the least painful way to solve this globally?