[ovs-dev] DNS support options
Ben Pfaff
blp at ovn.org
Tue Aug 8 19:48:15 UTC 2017
On Tue, Aug 08, 2017 at 02:59:21PM -0400, Lance Richardson wrote:
> > From: "Ben Pfaff" <blp at ovn.org>
> > To: dev at openvswitch.org
> > Sent: Tuesday, August 8, 2017 2:43:17 PM
> > Subject: [ovs-dev] DNS support options
> >
> > Open vSwitch currently supports only IP addresses for specifying
> > OpenFlow and OVSDB remotes. It would be nice to support DNS names.
> > Open vSwitch can't afford to let DNS resolution block processing, so it
> > needs some way to resolve DNS asynchronously. I've come up with the
> > following solutions so far:
> >
> > * Implement it ourselves using threads. Probably, this would be
> > a single worker thread that loops through calls to
> > getaddrinfo().
> >
> > * glibc has getaddrinfo_a(), an asynchronous version of
> > getaddrinfo(). *BSD and Windows do not have this function, so
> > we would still need to implement it ourselves (probably using
> > threads) if we adopted this approach, so it might be more work
> > than the first solution.
> >
> > * Use an external asynchronous DNS library. GNU adns looks like
> > a good choice: http://www.chiark.greenend.org.uk/~ian/adns/.
> > It has a port to Windows but I don't know whether it's
> > up-to-date.
> >
>
> With adns_beforepoll()/adns_afterpoll(), it looks like adns might be easy
> to integrate on top of lib/poll-loop.c. Not requiring a separate thread
> seems like a plus.
Oops, I just realized that adns is GPL'd, which means that linking it
against OVS would force OVS to be GPL'd, so it's probably not a good
choice.
Other possible choices:
- c-ares (https://c-ares.haxx.se/). Main disadvantage seems to
be that it's very "select" oriented.
- UDNS (http://www.corpit.ru/mjt/udns.html). May not be well
maintained--last release in 2014. Does not fall back to TCP
if necessary. Port to Windows exists, don't know whether it's
up-to-date.
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