Specify servers for `dns.lookup(...)`

[szmarczak]

The performance of Resolver.resolve4/Resolver.resolve6 is very poor (~15 ops/sec).

As I see it, it does the same as dns.lookup but you can select custom DNS servers as well as you can also get the TTL.

The performance of dns.lookup is ~6000 ops/sec. Is it somehow possible to select the servers for dns.lookup?

[silverwind]

Is it somehow possible to select the servers for dns.lookup?

Regular dns methods use the servers set by dns.setServers before the query.

The performance of Resolver.resolve4/Resolver.resolve6 is very poor

Can't say I noticed this. Do you have an minimal benchmark?

[szmarczak]

Regular dns methods use the servers set by dns.setServers before the query.

Okay, except this is global. All things that use the dns module will be affected.

Can't say I noticed this. Do you have an minimal benchmark?

Yup: https://github.com/szmarczak/cacheable-lookup/blob/master/benchmark.js

dns#resolve4 x 27.03   ops/sec ±41.64% (246 runs sampled)
dns#lookup   x 5,994   ops/sec ±0.26%  (285 runs sampled)

[silverwind]

this is global

Yeah, dns.Resolver is your only option then.

Regarding your benchmark, you have to keep in mind that all resolve variants contact your DNS server while lookup does not involve DNS or the network (on Linux, it's just a glibc call), so lookup will be faster by a magnitute in all cases. I'd be surpised if there were any major performance difference between dns and dns.Resolver methods.

And to answer your question on servers/TTL for lookup: It is not possible because underlying calls like getaddrinfo have no concept of servers or TTL (caching is done on OS level instead).

[szmarczak]

And to answer your question on servers/TTL for lookup: It is not possible because underlying calls like getaddrinfo have no concept of servers or TTL (caching is done on OS level instead).

Very well explained, I understand now :)

you have to keep in mind that all resolve variants contact your DNS server while lookup does not involve DNS or the network (on Linux, it's just a glibc call)

So dns.setServers() won't affect dns.lookup()?

no concept of servers

Thank you for your help :)

[sam-github]

@szmarczak you crossed out your question about setServers() and dns.lookup()?

The answer is "no", for posterity. Its implied by https://nodejs.org/api/dns.html#dns_dns_lookup to someone who knows how the system resolvers work and are configured, but your question makes me think it should be stated more explicitly.

https://nodejs.org/api/dns.html#dns_dns_setservers_servers use the word "resolution" in its text, but maybe that's not explicit enough, and a note to the effect that it does not effect dns.lookup() should be added.

[szmarczak]

you crossed out your question about setServers() and dns.lookup()?

@silverwind has given the answer already:

It is not possible because underlying calls like getaddrinfo have no concept of servers or TTL

your question makes me think it should be stated more explicitly.

Indeed.