[ovs-dev] DNS support feature (was: Re: DNS support options)

[Yifeng Sun]

Thanks Mark for your reply.

There is one more thing. If we bring DNS into play, we may need a mechanism
to watch for changes of ip addresses that were already resolved and being
used.

Thanks,
Yifeng

On Thu, Oct 26, 2017 at 12:10 PM, Mark Michelson <mmichels at redhat.com>
wrote:

> On Wed, Oct 25, 2017 at 4:16 PM Yifeng Sun <pkusunyifeng at gmail.com> wrote:
>
>> I feel that unbound stands out in the available open source DNS resolver.
>>
>> Below is the summary for unbound:
>> * The actual resolving work is done by a background process or thread. A
>> background process or thread seems unavoidable. Linux's getaddrinfo_a
>> clones a thread similarly.
>>
> * It is ported on Linux, BSD, Windows, MacOS/X and Solaris/SPARC. This is
>> good because OVS runs on a large range of platforms.
>>
> * It complies to the standard, with optional DNSSEC support. Some of its
>> features may not be needed in our case.
>> * The unbound context is thread-safe. Its internal locks may bring some
>> overhead. But since the DNS resolving is not frequent in OVS, I suppose
>> this small overhead is not an issue.
>>
>> Unbound looks like a good option. Another option is to create a
>> background thread which processes DNS resolving requests from the main
>> thread and sends back the resulting events to the main thread. This method
>> is quite simple and straightforward.
>>
>> The above are what I got so far. Please give your thoughts, thanks a lot.
>>
>
> If portability to all of the systems you mentioned in your second bullet
> point is important, then you can rule out a couple of options:
> * getaddrinfo_a is a GNU extension and is only available with glibc
> * The resolver functions[1] are a BSD specification so they'd be available
> on most platforms, but not on Windows. I don't personally recommend these
> because of the need to manually parse the DNS responses you receive.
>
> That leaves two options:
> * Run a background thread uses getaddrinfo() to perform resolution.
> * Use a third-party library (like unbound).
>
> Of these two options, I feel like the third-party library is the better
> option. The only downside I can think of is the extra dependency for OVS.
> And as far as what third-party library to use, I was the one that suggested
> unbound in the first place, so obviously I'm fine with using it :)
>
> Mark
>
> [1] http://man7.org/linux/man-pages/man3/resolver.3.html
>
>
>>
>> Below is the link for original discussion:
>> https://mail.openvswitch.org/pipermail/ovs-dev/2017-August/337038.html
>>
>>
>>
>> On Wed, Oct 25, 2017 at 2:11 PM, Ben Pfaff <blp at ovn.org> wrote:
>>
>>> Hello everyone, please allow me to introduce Yifeng Sun (CCed), who
>>> recently joined VMware's Open vSwitch team.  I've asked Yifeng to start
>>> out by working on DNS support for Open vSwitch.  Yifeng, can you tell us
>>> about what you've discovered so far, based on this thread from August
>>> that I'm reviving, and your tentative conclusions?
>>>
>>> Thanks,
>>>
>>> Ben.
>>>
>>
>>