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Use preferred protocol first when resolving hostname #728

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merged 5 commits into from
Jan 5, 2021

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yegle
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@yegle yegle commented Jan 3, 2021

Prior to this change, LookupIPAddr() is used to do the DNS query,
which sends two DNS queries for A/AAAA records, even if the config has
preferred protocol set to ip4 and does not allow fallback protocol.

This change will change to use LookupIP() with the preferred protocol,
and only try fallback protocol if it's set to true. In most cases doing
this will save one RTT of DNS query.

Fixes #724

@yegle
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yegle commented Jan 3, 2021

cc @brian-brazil

Prior to this change, LookupIPAddr() is used to do the DNS query,
which sends two DNS queries for A/AAAA records, even if the config has
preferred protocol set to ip4 and does not allow fallback protocol.

This change will change to use LookupIP() with the preferred protocol,
and only try fallback protocol if it's set to true. In most cases doing
this will save one RTT of DNS query.

Signed-off-by: Yuchen Ying <[email protected]>
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@brian-brazil brian-brazil merged commit 847b668 into prometheus:master Jan 5, 2021
@brian-brazil
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Thanks!

@yegle
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yegle commented Feb 2, 2021

I wonder if a new version can cut with this PR included?

Or alternatively can you publish a nightly docker image?

@crockk
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crockk commented Apr 27, 2021

Does the docker image at prom/blackbox-exporter:master include this merge?

@hferreira23
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@crockk It should be even though I'm actually using the master tag image and I see no change in the behavior.

Either way this PR will be on 0.19 which for the looks of it it's just around the corner.

roidelapluie added a commit to roidelapluie/blackbox_exporter that referenced this pull request May 28, 2021
@james58899
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Also related to golang/go#45024, need wait golang 1.17 release and upgrade.

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icmp: Both A and AAAA records are queried regardless of preferred_ip_protocol/ip_protocol_fallback
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