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What Is This
NetKernel Thing
Anyway?

Darren Cruse
August 5, 2010
(for the Lambda Lounge of St. Louis)
Wednesday, August 11, 2010

Preface
(one slide answers all)


What’s This NetKernel Thing?
• A “REST Based Microkernel”
• Written in Java
• Originally developed at HP Labs over 10 years ago
• Started life as an XML framework ala Cocoon
• Generalized over 4 versions into a general purpose
“Resource Oriented Computing” framework (though
it maintains esp. strong XML support).
• The main guys split off from HP and formed their
own company called 1060 Research Limited
• It’s sold under a dual source license - i.e. free for open
source projects, paid for commercial projects.

(that was the short answer -
now the longer one)


Chapter 1:
Lots of Computers
(macro)


In the Beginning There
Was One Computer

• Plus a 300 baud modem
• I had hair
• Things were simple then
(BASIC built in the ROM!)


State Of The Art

• 0.89 MHz Processor
• 4K RAM
• 192 x 128 Screen
Resolution
• Audio Cassette Storage


And That Computer
Begat Other Computers


And They Begat Some
More...


And so on...


And The World Became Awash
(in computers)


They Climbed Into Our
Pockets


And A Lot Had Changed.
(Since The Time That I Had Hair)


But Not So Much About
The Way We Program


Chapter 2:
Lots of Computers
(micro)


http://www.drdobbs.com/architecture-and-design/184405990

Dude -What Happened To 4 GHz?

Moore No More?
(nope - but it’s a different world)


“The Multi-Core Problem”
What This Means For Software: The Next Revolution
The revolution in mainstream software development from structured programming
to object-oriented programming was the greatest such change in the past 20 years,
and arguably in the past 30 years. There have been other changes, including the
most recent (and genuinely interesting) naissance of web services, but nothing that
most of us have seen during our careers has been as fundamental and as far-reaching
a change in the way we write software as the object revolution.

Until now.

Starting today, the performance lunch isn’t free any more. [...] But if you want your
application to beneﬁt from the continued exponential throughput advances in new
processors, it will need to be a well-written concurrent (usually multithreaded)
application. And that’s easier said than done, because not all problems are inherently
parallelizable and because concurrent programming is hard.

Edited from: “The Free Lunch is Over”, Herb Sutter
(http://www.drdobbs.com/architecture-and-design/184405990)


Postscript to Chapters 1 & 2
(in case it’s not obvious)

What’s the connection between “lots of computers on
the network” (chapter 1) and “lots of cores on a cpu
die” (chapter 2)?

The answer: Stuff running in Parallel


Chapter 3a:
The Web


Chapter 3a:
The Web
(of Lies and Deceit)


“Oh yeah the guys are using this new thing Service Oriented
Architecture.

They put their software on a whole bunch of servers. That
means it’s guaranteed to scale and have good performance
and be like super super reliable.

It’s really simple it uses this new thing called SOAP. That
stands for simple something or other. All they have to do is
connect up these “service” things how hard could that be.

And they said something called REST I don’t what that is but
it sounds easy too I guess it’s so easy the developers get to
rest.

It’s going to save us lots of time and money it really sounds
great.”
Actual made up conversation
between Product Managers, Circa 2003

Chapter 3b:
The Web
(for real this time)


The Web is a Very Successful
“Distributed System”
(with some very nice qualities)

✓ Flexibility
★ It's fairly easy to rearrange things at the server/network level, e.g.
move a document (or dynamic “service”) from one node to another.

✓ Heterogenous Technologies
★ Different servers can easily use different technologies (e.g. different
languages).

✓ Scalability
★ In general, services scale easily, if they're stateless and placed behind
multiple machine clusters with load balancers.

✓ Availability / Ease of Deployment
★ As long as you have at least two servers running the service, you can
hot deploy services leaving the old service running for a time while
you're starting the new service ("rolling restart").

RESTful HTTP Based Services
(bring the web’s benefits between servers)
b
a
l Service 1
a
l
App n
o
c
a Server
e Service 1
d
r
Browser
b
a
l b
a a
n l Service 1
c a
App
e n
Server c
r
e Service 2
r

NetKernel Modules and “Micro-Services”
(bring the web’s benefits inside servers, as well as between)
b
a
l
a
l
n
o
c
a
e
d
r
Browser
b
a
l b
a a
n l
c a
e n
r c
e
r

So what are these granular services doing
“inside” my program?
(revisiting those nice web qualities)

✓ More Flexibility
★ Now there’s more opportunities to easily change things (e.g. change your
persistance strategy for some resource), often with just a conﬁguration change.
★ And more opportunities to rearrange things on the network, e.g. moving a
module to a different server and talking to it with some remote protocol instead
of NetKernel’s in memory protocol.
★ Partly this is possible because of NetKernel’s caching which replicates local
representations of remote resources just like a browser would (the reason it’s
called “REpresentational State Transfer”! :).



✓ More Heterogenous Technologies
★ Easily use and intermix many of the popular JVM languages within a single
application. Java, Javascript, Groovy, JRuby, Scala, Clojure (experimental), Beanshell,
XSLT, XQuery, etc.
★ Add support for other languages if you’d like. Each language is supported by a
module called a “language runtime” and you can write your own as an “adapter” for
an existing tool. e.g. I added support for the Jakarta Velocity templating language
and it wasn’t hard.
★ Language runtimes follow the same REST principles which the rest of the system
does. e.g. In NetKernel, an XML file transformed to an HTML file via an XSLT is
much the same as a Groovy source file transformed to a class file by the Groovy
compiler runtime. Your groovy code will automatically be recompiled when you
modify it just as your html will be updated when you modify the xml. This applies
to any and all of NetKernel’s supported scripting languages.
★ As a consequence, under the new NetKernel Protocol you can even execute code on
a remote NetKernel server that physically resides on your local server. This is not a
feature “added on” to NetKernel so much as a natural consequence of it’s design.


✓ More Scalability
★ NetKernel’s internal multi-threaded scheduler is to internal requests, as a
load balancer is to a web or application server.
★ Resource “representations” are immutable.
★ Accessor methods should be coded to be thread safe i.e. stateless.
★ More cpu cores mean more throughput / more simultaneous requests
processed.
★ For faster response times, developers incorporate asynchronous requests to
run sub-requests in parallel.
★ Third party libraries that are not thread safe can be wrapped in a module
marked as such - in which case NetKernel will single thread them.
★ Representations that are not immutable can be locked explicitly - but this is
not typical usage of NetKernel (it’s more of an escape hatch for bad code :).



✓ More Availability / Easier Deployment
★ Modules can be hot deployed via the “Apposite” tool while a system is live and
running.
★ If problems are encountered the deployed module can be rolled back leaving
just the original module.
★ Modules are versioned and clients to services can indicate the version(s) they
desire.
★ This allows that multiple versions of the same module can be deployed
simultaneously. e.g. A “stable version” and a “release candidate” version.


The network really is the computer...
(and URIs are a sort of “machine independent” memory address)

“CLOUD OF RESOURCES”
N
E
T
W
O
R
K

NETKERNEL CACHE (IN- NETKERNEL CACHE (IN-
MEMORY) MEMORY)
B B
U U
S S

CORE 1 CORE “N” CORE 1 CORE “N”


You sound like a used car salesman.
(is this some kind of infomercial?)
“Just a note that I was skeptical of NetKernel until I tried it and got used to it a little
bit.

It helped me see some things I hadn’t realized before which is how many lost
opportunities I’d created in my “service oriented” system design because of how
different I was doing things inside my code from the way things are done between the
services.

To give a simple example, if I need to read a file in a program in java I typically write
some code and use the File object to read the file. I don't use "file://" like we do from
our browser. As a result, if I want to change where that information comes from, say
read it from a blob in Oracle, or read it from an XML database, or maybe a better
example: read it from another machine RESTFully using HTTP - each of those feel
like a fairly serious change, but not when everything has a URI like in NetKernel.”

Darren Cruse,
NetKernel Advocate (seriously)
and inventor of the “Ultra-Toe” Toe Nail Brightening System,
the only toe nail brightening system with Toe-nail-isol!!

Thanks for listening.
Reach me at:
darren.cruse@gmail.com

Watch me blab at:
http://bangthekeyboard.wordpress.com


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What's this NetKernel Thing Anyway?

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