Specify servers for dns.lookup(...) #25560

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1. silverwind commented on Jan 18, 2019

   

   silverwind

   on Jan 18, 2019

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   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?
2. szmarczak commented on Jan 18, 2019

   

   szmarczak

   on Jan 18, 2019

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   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)
3. silverwind commented on Jan 18, 2019

   

   silverwind

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   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).
4. szmarczak commented on Jan 18, 2019

   

   szmarczak

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   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 :)
5. szmarczak

   closed this as completedon Jan 18, 2019
6. sam-github commented on Jan 18, 2019

   

   sam-github

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   @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.
7. szmarczak commented on Jan 18, 2019

   

   szmarczak

   on Jan 18, 2019

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   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.