[erlang-questions] [ANN]: Damocles, a library for testing distribution scenarios on a single machine

Wed Jan 7 17:00:42 CET 2015

  Thanks for that. Yeah, I had a look at your tuntap library, and it looks
like both a portable way to reimplement the existing functionality, but
also some ways to add some features more easily that I intended anyway, and
some I had mentally dismissed as too unpleasant. I just need to find time
to play with it and confirm/evolve my mental model. I'm thinking I'm going
to try dropping one more feature on the existing code base, then start
experimenting on a branch. There's some complexity in managing multiple
destinations from one source, as well as the actual implementation of
drop/delay (I need to make it so queued packets don't chain their delay.
I.e., if I changed the code in that example to have a solid 1 second delay,
for every frame coming in, and I got 5 frames in rapid succession, I'd have
one received at the destination after one second, the next after two, the
next after three, etc. I need to track when I received them and apply rules
appropriately, across multiple nodes)

On Wed, Jan 7, 2015 at 10:20 AM, Michael Santos <michael.santos@REDACTED>
wrote:

> On Mon, Jan 05, 2015 at 08:55:06PM -0500, Christopher Phillips wrote:
> >   Hmm, I've had so little experience with tuntap interfaces I didn't
> think
> > of them. That sounds like the way to go to get things working on OSX,
> > though at a much larger amount of effort (both the learning curve on my
> > part, and re-implementing the degradation behaviors I get for free from
> the
> > kernel). Thanks for suggesting it; once I get things to where it's usable
> > on Linux in all the ways I want, some research and a rewrite may be in
> > order to get it fully portable.
>
> Sure, that is definitely reasonable.
>
> Working with tuntap devices isn't too difficult. For comparison, here is
> a very simple example that forwards ethernet frames over erlang
> distribution and randomly drops or delays a percentage of the frames:
>
> https://gist.github.com/msantos/f2823fcba40975003dc3
>
> Set up 2 distributed nodes:
>
>     erl -name n@REDACTED -setcookie CHOCOLATEBUTTERSCOTCH
>     erl -name n@REDACTED -setcookie CHOCOLATEBUTTERSCOTCH
>
> Then create the tunnel:
>
>     % Drop 10% of the frames, randomly delay 40% up to 1 second
>     wastrel:start('n@REDACTED', "10.1.1.1", "10.1.1.2", 0.1, 0.4).
>
> Try to login using ssh (or whatever)!
>
>     ssh 10.1.1.2
>
> Meh, I've had to use worse ...
>
> Notes:
> * relies on this erlang tuntap driver
>
>     https://github.com/msantos/tunctl
>
> * beam needs to be running as root or have CAP_NET_ADMIN set:
>
>     sudo setcap cap_net_admin=ep /usr/local/lib/erlang/erts-*/bin/beam*
>
> > On Mon, Jan 5, 2015 at 8:11 PM, Michael Santos <michael.santos@REDACTED
> >
> > wrote:
> >
> > > On Mon, Jan 05, 2015 at 09:16:42AM -0500, Christopher Phillips wrote:
> > > > For OSX ipfw was deprecated in Lion and removed in Yosemite. I've
> done a
> > > > bit of looking at the replacement, pf, and it looks like dropping
> packets
> > > > based on percentage is doable, as is bandwidth throttling (something
> I'd
> > > > like to add, in general), but I don't see any way to induce a delay,
> > > beyond
> > > > an implicit one based on tos prioritization. If someone knows how
> and can
> > > > point me in the right direction I'd appreciate it.
> > >
> > > The portable way is to use a tuntap device. Then you can arbitrarily
> > > drop packets, throttle bandwidth, introduce latency, whatever, from
> your
> > > code. Sort of like quickcheck for networks :)
> > >
> > > > On Mon, Jan 5, 2015 at 6:52 AM, Sergej Jurečko <
> sergej.jurecko@REDACTED
> > > >
> > > > wrote:
> > > >
> > > > > This looks like a great tool and something that could easily be
> added
> > > to
> > > > > unit tests.
> > > > > Anyone with ipfw skills to add bsd/osx support?
> > > > >
> > > > > Sergej
> > > > > On Jan 5, 2015 1:41 AM, "Christopher Phillips" <
> lostcolony@REDACTED>
> > > > > wrote:
> > > > >
> > > > >> https://github.com/lostcolony/damocles
> > > > >>
> > > > >> I asked a while back on this mailing list if anyone had any useful
> > > > >> libraries or similar for testing distribution scenarios. I only
> got
> > > back a
> > > > >> few responses (maybe co-op riak_test? Maybe make use of the
> underlying
> > > > >> Linux traffic control and network emulation apps?), and my own
> > > searches,
> > > > >> while finding a few libraries, didn't find anything I could easily
> > > co-op
> > > > >> for my purposes.
> > > > >>
> > > > >> To that end, I went ahead and spent part of my break on this, and
> it
> > > just
> > > > >> got sufficiently feature complete to throw out there. I haven't
> had a
> > > > >> chance to really start using it heavily, and I've only been
> testing
> > > it on
> > > > >> my dev box, but a basic run through of the functionality as I
> typed
> > > up the
> > > > >> readme worked (so any issues being pointed out would be
> appreciated).
> > > > >> Essentially, it allows you to create and manipulate local
> interfaces
> > > on a
> > > > >> Linux machine to emulate packet delay and loss (using the
> underlying
> > > > >> traffic control and network emulation mechanisms), with a number
> of
> > > > >> convenience methods to (hopefully) easily describe fairly
> intricate
> > > > >> distribution scenarios.
> > > > >>
> > > > >> Things like "create these 5 interfaces, (now from my test code,
> > > launch a
> > > > >> copy of my app on each one, or even a different app on one of
> them,
> > > to see
> > > > >> what happens when that resource is flaky); now make it so 1 and 2
> > > can't
> > > > >> talk to 3 and 4, and vice versa, but everyone can still talk to
> 5, but
> > > > >> replies have a 50% chance of being dropped from 5 when responding
> to
> > > 1 and
> > > > >> 2, and there's a 300ms delay between 3 and 4; (now, let's run
> more of
> > > our
> > > > >> test code to assert that trying to write to any node still
> succeeds);
> > > okay,
> > > > >> now let's restore the network back to normal (and have our test
> code
> > > make
> > > > >> sure the write was retained)", or whatever, can be set up in a
> > > > >> straightforward, automated manner as part of a common test run,
> and
> > > not be
> > > > >> reliant on certain VMs being up, nor the tests being run on a
> specific
> > > > >> network. The tradeoff, obviously, being that you can't really load
> > > test
> > > > >> things with it. Still, it fits my basic needs, and I figured it
> might
> > > be of
> > > > >> use to others.
> > > > >>
> > > > >> I'll be adding some simple examples when I next get free time (I
> ran
> > > out
> > > > >> of it from the holiday break without getting to them; dunno when I
> > > will),
> > > > >> and will try and get to any bugs or simple suggestions in a timely
> > > manner,
> > > > >> but hopefully it's fairly straightforward and useful as is.
> > > > >>
> > > > >> _______________________________________________
> > > > >> erlang-questions mailing list
> > > > >> erlang-questions@REDACTED
> > > > >> http://erlang.org/mailman/listinfo/erlang-questions
> > > > >>
> > > > >>
> > >
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> > >
> > >
>
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