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

Michael Santos michael.santos@REDACTED
Tue Jan 6 02:11:06 CET 2015

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.
> >>
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> >>
> >>

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