TCP support

[kuritka]

DNS runs primarily on UDP. Support TCP is low-hanging fruit. Roughly it is just a matter of changing the DNS server request settings.

TCP support has another - for contributor very important reason. If I'm not in an environment that supports UDP (e.g: colima) and I need to start debugging k8gb (in my case directly from my IDE), I have to make temporary changes in the dns.go file. Would be nice keep settings in ENV_VARS only.

Instructions

• Introduce a new config variable e.g.: EDGE_DNS_PORT EDGE_DNS_PROTOCOL

  • keep UDP as default protocol
  • cover by unit tests

• Fix the implementation in the utils package, e.g.:

        // something like this (localhost:1053 is defined in envvars as well):
 	// msg, err = dns.Exchange(m, ns.String())
        client := dns.Client{Net: "tcp"}
        msg, _, err = client.Exchange(m, "localhost:1053")

[somaritane]

@kuritka I'd suggest using EDGE_DNS_PROTOCOL, port is something that can be changed and it's not necessarily tied to a certain protocol type.

[kuritka]

@somaritane Hey, thanks for the heads up. Of course, I was referring to the protocol. My mistakes; Fixed

[goku321]

Hello. I would like to work on this :)

[ytsarev]

Hi @goku321 , amazing! I assigned this one to you :)