Re: FYI Netflix is down

[Brett Frankenberger <rbf+nanog () panix com>]

On Sat, Jun 30, 2012 at 01:19:54PM -0700, Scott Howard wrote:
> On Sat, Jun 30, 2012 at 12:04 PM, Todd Underwood <toddunder () gmail com>wrote:
>
> > This was not a cascading failure.  It was a simple power outage
> >
> > Cascading failures involve interdependencies among components.
>
> Not always.  Cascading failures can also occur when there is zero
> dependency between components.  The simplest form of this is where one
> environment fails over to another, but the target environment is not
> capable of handling the additional load and then "fails" itself as a result
> (in some form or other, but frequently different to the mode of the
> original failure).

That's an interdependency.  Environment A is dependent on environment B
being up and pulling some of the load away from A; B is dependent on A
beingup and pulling some of the load away from B.
    A Crashes for reason X -> Load Shifts to B -> B Crashes due to load
is a classic cascading failure.  And it's not limited to software
systems.  It's how most major blackouts occur (except with more than
three steps in the cascade, of course).

     -- Brett