Use TCP for weave dns.

[tomwilkie]

Fixes #1013

[rade]

We really should use golang's resolver. Alas it does not allow you to specify a server.

But if we have to do our own thing, we should at least do it correctly, i.e. try udp first and fall back to tcp if the answer is truncated. It's pretty simple to do and exactly what golang does

[tomwilkie]

But if we have to do our own thing, we should at least do it correctly, i.e. try udp first and fall back to tcp if the answer is truncated. It's pretty simple to do and exactly what golang does

Why? Whats the downside to just using TCP?

[rade]

Why? Whats the downside to just using TCP?

Protocol compliance. Alas you are off the hook. From RFC 5966:

Regarding the choice of when to use UDP or TCP, Section 6.1.3.2 of RFC 1123 also says:

 ... a DNS resolver or server that is sending a non-zone-transfer query MUST send a UDP query first.

That requirement is hereby relaxed. A resolver SHOULD send a UDP query first, but MAY elect to send a TCP query instead if it has good reason to expect the response would be truncated if it were sent over UDP (with or without EDNS0) or for other operational reasons, in particular, if it already has an open TCP connection to the server.

[2opremio]

@errordeveloper Can you test this? I have pushed an image called weaveworks/scope:1038-dns-tcp . You will also have to change the version in the scope script (I think you already know the drill ... )

[tomwilkie]

@errordeveloper reports this worked on slack. Ilya can you merge when you're happy?

[errordeveloper]

I will run a few more tests today to double-check.

On Thu, 25 Feb 2016 16:42 Tom Wilkie notifications@github.com wrote:

@errordeveloper https://github.com/errordeveloper reports this worked
on slack. Ilya can you merge when you're happy?

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#1038 (comment).

[errordeveloper]

@rade I think we do have a good reason here, as answer is expected to be truncated, as we currently have several records for each host and in #1013 it ended up with 15 records for 5 hosts.

[rade]

I think we do have a good reason here

yes, which is why I said "you are off the hook".