Re: [MirageOS-devel] irmin + mirage-vnetif + alcotest + good ol' arp

[Anil Madhavapeddy <anil@xxxxxxxxxx>]

On 10 Apr 2015, at 05:39, Mindy <mindy@xxxxxxxxxxxxxxxxxxx> wrote:
> 
> On 04/09/2015 07:30 PM, Thomas Gazagnaire wrote:
>>> I'm not that far into doing anything interesting with this pile of code, 
>>> but I wanted to solicit your thoughts and feedback given all the mumbling 
>>> and general noise-making about testing we've been doing.
>>> 
>>> Thanks for your consideration and support. :)
>> That's awesome!
>> 
>> I haven't checked the code yet, but is the mapping bi-directionnal, i.e. can 
>> you modify the ARP table in the Git repository, commit and then it's picked 
>> up by the ARP code?
> Yes, it should work this way (once there's more code in place).
<...>
>> Not related to testing, but that would be cool to find a clever use for git 
>> pull/push between unikernels (replacing ARP broadcast maybe?)
> I'd been thinking about (or maybe remembered talking about with someone 
> else?) pre-seeding newly booted unikernels with caches reflecting the current 
> state of the local network, which is a less general case of what you propose.

That was me -- the idea is tied into the above two points I've quoted.  Once 
you establish Irmin as a trusted communications channel between two unikernels, 
then you can start using it to feed in state as well.

ARP broadcast is obviously a very legacy way to discover other hosts on the 
network, and so is one of the first places where we could start providing a 
migration path away from rather high-latency mechanisms such as multicast DNS 
and broadcast protocols, towards something that can very efficiently 
communicate a change of states to all other nodes.  In addition to being more 
efficient, it's also easier to build a stronger trust model ("where did this 
ARP update come from? Why is it different from all the other nodes? I refuse to 
merge!").

Of course, the extremely cool thing about Irmin's bidirectional mappings is 
that existing hosts can still bridge into the Irmin communication system just 
by sending a normal protocol packet!  So Luke's hard work on mDNS isn't 
obsolete for a few decades yet :-)

-anil
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