Review and update DNS-resolver doc

[mayorova]

The document https://github.com/3scale/APIcast/blob/bcd00e0/doc/dns-resolver.md mentions dnsmasq, howerver dnsmasq is not forming part of the APIcast image anymore, see #1090 and https://issues.redhat.com/browse/THREESCALE-1555.

Some other info in the doc might still be relevant though, but it needs to be reviewed and updated according to the current state.

[hector-vido]

Hi @mayorova, how about add in docker-compose a dnsmasq container with --add-host pointing to Porta address and use --dns pointing to this new dnsmasq in apicast container?

If this looks good to you, I can add this to the project.

[tkan145]

@hector-vido I think the purpose of this ticket is to review and remove dnsmasq from the documentation since we no longer rely on dnsmasq to resolve DNS queries. Therefore, re-adding the dnsmasq container makes no sense to me.

[hector-vido]

@tkan145 sorry, I totally misunderstood and forgot that the containers will relay in docker internal DNS resolver and adding entries in our local /etc/hosts is enough. I was reading it from the perspective of a developer trying to test APICast, but I was wrong any way.

[tkan145]

No need to sorry 😃

fyi, the resolver logic is located here https://github.com/3scale/APIcast/blob/master/gateway/src/resty/resolver.lua

[akostadinov]

Just FYI, adding entries to /etc/hosts is NOT enough. To run apicast locally in a container, we use a small proxy called porxy to be accessed by IP and relay requests to the porta server with the correct Host header.