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Date: Thu, 28 Sep 2017 15:45:28 +0530
From: Srinivasa Raghavan <raghav135@...il.com>
To: musl@...ts.openwall.com
Subject: DNS resolution happenning only after timeout

Hi,

When using "Alpine" docker image which uses musl-libc, we are facing delay
when we do operations like below in our production environment,
1. ping <name>
2. nslookup <name>
3. traceroute <name>
4. http request from node.js

There is a 5 second delay in name resolution, and then the above command
returns the response. The same problem does not occur in "debian" docker
image (which uses GNU libc).

In our case, there is a combination of SERVFAIL, "canonical name" along
with "Non authoritative answer".

Some learnings after doing some trial and error:
1. If I install "bind-tools" package in alpine, the "nslookup" happens
without delay.
2. If I set "options timout:1" in /etc/resolv.conf , then the name is
resolved after 1 second (instead of 5 seconds).
3. Whatever I change in /etc/resolv.conf (Like setting "domain", "search"),
there was no benefit.
4. output of "host"/"nslookup" command shows "SERVFAIL"
5. The problem does not occur if run from the host machine (Not from alpine
container).
6. The problem does not occur if run from another container which uses Gnu
libc, like "Debian" image.

Sample command outputs attached for reference.

Request you to kindly help in debugging / resolution of this.

Kind Regards,
R. Srinivasa Raghavan.

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