General-Purpose, Internet-Scale Distributed Computing with Linked Process

General-Purpose, Internet-Scale Distributed
Computing with Linked Process

Linked Process

Marko A. Rodriguez
T-5/Center for Nonlinear Studies, Los Alamos National Laboratory
http://markorodriguez.com

September 10, 2009

1

Abstract

There are many distributed computing protocols in existence today. Some serve
as a solution for scientiﬁc computing, some as a middleware solution to large-
scale systems engineering, and others as an “easy-to-use” service solution on the
Web. What most of these protocols have in common is that they require a
strong “handshake” between the machines utilizing each other’s resources. This
coupling has rendered many distributed protocols to only be useful for a collection of
machines owned and operated by a single organization (e.g. MPI/PVM computing)
or for use by foreign machines with a very speciﬁc use case (e.g. RPC/Web Services
computing). The former allows for general-purpose distributed computing and
the latter allows for Internet-scale distributed computing. What if both types of
functionality were to be merged? What does a general-purpose, Internet-scale
distributed computing protocol look like?

Linked Process [ http://linkedprocess.org ]

Center for Nonlinear Studies – Los Alamos, New Mexico – September 10, 2009

2

A General-Purpose Requirement

• General-purpose: it is required that the code executed is not
necessarily defined by the executing device, but instead can be
defined by the requesting device.
Language-agnostic: it is required that distributed code can, in
principle, be written in any computer language.
Safe: it is required that the execution of code be confined by clearly
specified permissions on the executing device.
Accessible: it is required that various types of computing resources
be accessible when permissions allow.

The notion of “general-purpose” is not defined according to a single dimension as there are various general-purpose approaches

which each attain certain types of generality. Please be generous in your interpretation of this term for the time being.


3

An Internet-Scale Requirement

• Internet-scale: it is required that any device with an Internet connection
(from a cell phone to a supercomputer) be able contribute and leverage
computing resources.
Decentralized: it is required that the computing resources are not
centralized or controlled by any one party.
Discoverable: it is required that devices be discoverable by other
devices needing to leverage their resources.
Transient: it is required that devices coming online and oﬄine are
easily incoporated and removed.

The extreme notion of “Internet-scale” goes beyond the 32-bit addresses of the IP protocol. There are more than 4,294,967,296

devices on the Internet. Thus, at the extreme, “Internet-scale” refers to all devices that can communicate and be communicated

with through the Internet.


Outline
LoP
4

• An Introduction to Other Distributed Computing Protocols
General-Purpose Distributed Computing with MPI
Internet-Scale Distributed Computing with Web Services

• An Introduction to the Linked Process Protocol
Internet-Scale Distributed Computing with Linked Process
General-Purpose Distributed Computing with Linked Process

• An Introduction to the Linked Process Protocol Implementation

• Current and Future State of Linked Process


Outline
LoP
5






6

A Short Note on Other Protocol Discussions

• The symbol “ ” means that this feature is good with respect to the
two previous requirements.

• The symbol “ ” means this feature is bad with respect to the two
previous requirements.

There are always tradeoﬀs in computing. These are not “objective”
valuations of the protocols discussed next. Valuations are in terms of the
requirements set forth for the design of Linked Process. Linked Process
won’t solve all problems—it is “yet another distributed computing
protocol” that has a collection of unique features that make it useful for
problems with the aforementioned requirements.


Outline
LoP
7






8

General-Purpose: Distributed Computing with MPI
• The Message Passing Interface (MPI) is a language agnostic protocol
for inter-process communication.

• Processes (i.e. threads of execution) communicate by passing data
between each other (i.e. messages).
send(&x, p2): send data pointed to by x to process p2.
recv(&y, p1): receive data from process p2 and store it at y .

process 1 process 2
int x[100]; int y[100];
... ... time
... ...
send(&x, 2); recv(&y, 1);


9


marko> more hosts.txt
machine1
machine2
marko> mpirun -machinefile hosts.txt -np=3 myProgram
spawning myProgram on machine1...
Executing...
Done. Thank you, compute again.
marko>

Within myProgram the code branches depending on which “rank” its process is (e.g., with respect to the above example, rank is

either 1, 2, or 3). This way, each processor is doing a task particular to its self/rank.


10


MPI has been around since the early 1990’s and is a thoroughly applied
protocol with various language ports (however, MPI tends to be more
“C/Fortran”-ish as its intended use if high-performance computing).
[Language-agnostic]

MPI developers have access to all machine resources—the limiting
factor being the operating system. [Accessible]

MPI implementations have large libraries of useful distributed computing
patterns (e.g. scatter/gather, broadcast, reduce, etc.). What you can
think of is what you can do. [General-purpose]


11


MPI requires the MPI agent mpirun to have “ssh” access to the
physical devices that processes will be spawned on (i.e. the operating
system becomes the security manager). [Safe]

MPI processes have low-level access to the computing resources
of the underlying machine and thus, introduces a security risk for
foreign/unknown code. In short, you most likely own all your machines.
[Decentralized]

MPI requires a set of machines and the compilation of all code before
execution. [Transient]


12

An Artist’s Interpretation of MPI

.3
0.0
.1
0.0
.2 .0.0
. . 127
127 127

[1,2,7,9]
['c','b']

[1]
[42,31]


Outline
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13






14

Internet-Scale: Distributed Computing with
Web Services

“Web services are frequently just Internet Application
Programming Interfaces (API) that can be accessed over a network,
such as the Internet, and executed on a remote system hosting the
requested services.”

—from Wikipedia’s Web Services article.

• A Web Service is like an API.

• A Web Service is hosted by a remote device and can be accessed by
anyone over the network.


15

Web Services
• REST-based (REpresentational State Transfer) Web Services make use
of simple HTTP-based APIs. REST “verbs” are GET, PUT, POST, and
DELETE.
resource
http://chart.apis.google.com/chart?
cht=p3&chd=t:60,40&chs=250x100&chl=LANL|Sandia
parameters


16

Web Services
• RPC-based (Remote Procedure Call) Web Services perform a set of
functions with a speciﬁcation for sending process requests and receiving
process results (e.g. Web Service Description Language – WSDL).

Web Service 127.0.0.2

boolean aMethod(String x, int y);
double bMethod(double z);

Service Requestor 127.0.0.1

void cMethod() {
Object[] params = {"marko", 29};
Stub s = new Stub("aMethod", params);
boolean b = s.execute();
}


17

Web Services

Most modern languages have libraries to support the various Web
Services models. They usually make use of “Web” protocols (e.g. HTTP)
and encodings (e.g. XML, SOAP, JSON). [Language-agnostic]

Limited functionality and strict interfaces ensures that underlying
devices can not be compromised. [Safe]

Web Service models have discovery mechanisms to locate services that
perform a particular function and take particular types of inputs and
produce particular types of outputs (e.g. UDDI). [Discoverability]

Web Services are web addressable and intended for use by anyone (not
just the developer of the service). [Internet-scale]


18

Web Services

Web Services are defined for particular use cases and thus, the
computing resources offered by a Web Service are defined by the developer
of the Web Service. [General-purpose]
• e.g. Google Charts codebase is defined and can be used, but only for
what it was created for (namely, to make graphical charts).

Web Services are tied to the Internet Protocol for device addressing and
thus, reduces the types of devices that can offer services. [Internet-scale]
• i.e. its difficult to run a typical HTTP-based Web Service off my cell
phone without some intermediary gateway mechanism.


19

An Artist’s Interpretation of Web Services

f(x)

f(object)
.2
.0.0
object 127

.1
.0.0
127

g(object) g(x)

object

.0.0.3
127


Outline
LoP
20






21

Core Features of Linked Process

• Linked Process entities are not addressed by IP addresses. Their
addressing scheme is location independent.
Implication: Any device with an Internet connection can
support or leverage a Linked Process cloud. Linked Process clouds
support Internet-scale distributed computing.

• Linked Process allows users to execute any code on a remote device as
long as the code does not violate set security permissions.
Implication: Code is migrated to remote devices for execution.
Linked Process clouds support general-purpose distributed
computing.


22

An Artist’s Interpretation of Linked Process

.0 .0.2
127

.1
0.0
1 27.

.3
.0.0
127


Outline
LoP
23






24

Internet-Scale: XMPP Communication Protocol

• Linked Process rides atop the eXtensible Messaging and Presence
Protocol. This is what gives Linked Process its Internet-scale quality.

• XMPP was developed as an open protocol for Instance Messaging (GTalk,
iChat, Jabber, etc.). Servers to cells phones can send and receive chat
messages.

• Interesting aspects of XMPP that make it useful for Internet-scale
distributed computing.
XMPP creates a communication layer of abstraction above IP.
XMPP servers are XML packet routers between XMPP clients.
XMPP is an asynchronous message passing protocol.


25

Internet-Scale: XMPP creates a communication layer of
abstraction above IP
• XMPP clients are identiﬁer by Jabber IDs (JID).
an example XMPP client JID is marko@lanl.gov
XMPP clients are IP independent.

• XMPP clients log into XMPP servers.
an example XMPP server JID is lanl.gov
XMPP servers are IP dependent.

• XMPP clients maintain the same JID irrespective of their physical
location (i.e. IP address). Think of how your IM chat client operates.
marko@lanl.gov is my JID irrespective of its logged into the XMPP
server from a Los Alamos IP, New York IP, or Swedish IP.


26

Internet-Scale: XMPP servers are XML packet routers
between XMPP clients
marko@lanl.gov/1234 josh@rpi.edu/5678
127.0.0.1

127.0.0.4
Client Client

<packet t=1 <packet t=3
to="josh@rpi.edu" to="josh@rpi.edu"
from="marko@lanl.gov" /> from="marko@lanl.gov" />
127.0.0.2

127.0.0.3
Server <packet t=2 Server
to="josh@rpi.edu"
from="marko@lanl.gov" />
lanl.gov rpi.edu

marko@lanl.gov/1234 and josh@rpi.edu/5678 are fully-qualified client JIDs. Many clients (i.e. applications) can exist off the

same bare JID (e.g. marko@lanl.gov). Also, addresses can be fully-qualified to route the packet to a particular client.


27

Internet-Scale: XMPP is an asynchronous
message passing protocol
marko@lanl.gov/1234 josh@rpi.edu/5678
127.0.0.1

127.0.0.4
Client Client

<stream> <stream>
... ...

<stream> <stream>
... ...

<stream>
127.0.0.2

127.0.0.3
...
Server Server
<stream>
...
lanl.gov rpi.edu


28

Internet-Scale: XMPP is an asynchronous
message passing protocol

• My outgoing stream from my marko@lanl.gov XMPP client to the
lanl.gov XMPP server. Note that any XML can be sent between
clients. This is what makes XMPP “extensible.”
<stream>

<message from="marko@lanl.gov" to="josh@rpi.edu">
<body>It is a near must that you read my blog.</body>
</message>
<iq from="marko@lanl.gov" to="farm@rpi.edu">
<spawn_vm vm_species="groovy" vm_id="ABCD" />
</iq>
<message from="marko@lanl.gov to="vadas@lanl.gov">
<body>What is up with that Mike guy?</body>
</message>
</stream>

Outline
LoP
29






30

General-Purpose: Language-Agnostic Code Migration
• Linked Process supports the migration of code (i.e. software, computing
instructions, etc.) between devices.

• Migrated code is intended to make use of the computing resources of
the device (e.g. clock cycles, software APIs, hardware components, data
sets, etc.)

• Migrated code can be in any computer language as long as the executing
device maintains an appropriate virtual machine to execute code in that
language.

• Devices in Linked Process serve as “computing sandboxes” that can be
leverage for the execution of any code as long as the code does not
violate set security permissions.


31

General-Purpose: Code Permissions
permission description type
job timeout milliseconds for which a job may execute text-single
vm time to live milliseconds for which a virtual machine may exist text-single
shutdown farm exit the farm process boolean
execute program execute a program boolean
read file read from a file list-multi
write file write to a file list-multi
delete file delete from a file list-multi
open connection open a socket connection boolean
listen connection wait for a connection request boolean
access print job initiate a print job request boolean
... ... ...

This set of permissions is not exhaustive. The Linked Process specification has a collection of REQUIRED and RECOMMENDED

permissions. Moreover, deployers may which to extend the collection to support environment specific conditions (e.g. database

access). Finally, these permissions are made available through disco#info service discovery (XEP-0030).


32

General-Purpose: Linked Process Hierarchy

Registry

Cloud Countryside Farm Virtual Machine Job

Villein

Linked Process entities contain/maintain/manage/etc. other Linked Process entities.


33

General-Purpose: Linked Process Entities

LoP
Cloud: A top-level construct which groups all farms, registries, and virtual machines
to which a villein has access.
Countryside: Many entities can exist on a single countryside (a bare JID).

Farm: A farm is the gateway to the device’s resources and exists on a countryside.
In general, there is one farm for each device. [SUPPORTS A CLOUD]

Virtual Machine: A virtual machine is spawned from a farm and is the primary
engine of computation in a cloud. [SUPPORTS A CLOUD]

Villein: A villein is an application that leverages a cloud for computational resources
(e.g. clock cycles, software, data sets, etc.). [LEVERAGES A CLOUD]

Registry: A registry is responsible for maintaining a roster of countrysides
and publishing only those countrysides that have active farms on them (based on
<presence/>).


34

General-Purpose: Linked Process Packets
• <spawn vm/>: create a virtual machine of a particular species
(i.e. language such as JavaScript, Ruby, Python, Groovy, etc.).

• <submit job/>: execute the provided instructions/expressions.

• <ping job/>: determine the status of a previously submitted job.

• <abort job/>: cancel a previously submitted job.

• <manage bindings/>: set or get virtual machine variables.

• <terminate vm/>: destroy the virtual machine process.

NOTE: This presentation does not discuss interactions with registries, just farms and
virtual machines.


35

General-Purpose: A Villein and Farm
marko@lanl.gov/1234 test_countryside@lanl.linkedprocess.org/LoPFarm/60KES71Y

This is a screenshot from the LoPSideD GUI package. In practice, villein and farms usually don’t have this GUI front-end. This

package was developed to make it easier for developers to debug their Linked Process code. However, for farm providers, its a

way to see villeins communicating with their farm and to inspect the ﬂow of packets and the state of existing virtual machines.


36

General-Purpose: A Villein and Farm

This villein and farm are on diﬀerent physical devices. The villein is made aware of the farm because the villein is subscribed to

the farm’s countryside. Thus, all <presence/> packets coming from the countryside are delivered to the villein. The

subscriptions of the villein are available in its roster.


37

General-Purpose: Basic Communication Sequence

marko@lanl.gov/1234 test_countryside@...60KES71Y f472fb16...

127.0.0.1 127.0.0.2
get
<spawn_vm/>
result
<spawn_vm/>
get
<submit_job/>
result
<submit_job/>
get
<terminate_vm/>
result
<terminate_vm/>


38

General-Purpose: Spawning a Virtual Machine

• GET sent from a villein to farm...
<iq from="marko@lanl.gov/1234"
to="test_countryside@...60KES71Y" type="get" id="xxxx">
<spawn_vm xmlns="http://linkedprocess.org/2009/06/Farm#"
vm_species="javascript" />
</iq>

• RESULT sent from the farm to the villein...
<iq from=test_countryside@...60KES71Y"
to="marko@lanl.gov/1234" type="result" id="xxxx">
<spawn_vm xmlns="http://linkedprocess.org/2009/06/Farm#"
vm_id="f472fb16..." vm_species="javascript" />
</iq>


39


The use of disco#info (XEP-0030) allows a villein to discover what features and other information a farm supports. This is how

the villein knows that the farm allows for the spawning of Python, JavaScript, Groovy, and Ruby virtual machines.


40


The spawned virtual machine has an identiﬁer that is unique to its parent farm. The virtual machine maintains a state that is

altered through job submissions and binding updates. The virtual machine’s state is destroyed when the virtual machine is

terminated.


41

General-Purpose: On the Nature of Virtual Machines

• Virtual machines are controlled by a farm—the farm serves as the
“operating system” to control resource consumption and permissions of
a virtual machine.

• Virtual machines maintain their state throughout their lifetime. In other
words, in general, the order in which jobs are executed matters.

• Virtual machines are speciﬁc to a particular computer language and
can be naturally thought of as an “XMPP-wrapped” runtime terminal.
(e.g. groovy> 1 + 2;).


42

General-Purpose: Submitting a Job

• GET sent from a villein to virtual machine (indirectly through the farm)...

<submit_job xmlns="http://linkedprocess.org/2009/06/Farm#"
vm_id="f472fb16...">
var temp=0;
for(i=0; i<10; i++) {
temp = temp + 1;
}
temp;
</submit_job>
</iq>


43

• RESULT sent from the virtual machine to the villein (indirectly through
the farm)...

<iq from="test_countryside@...60KES71Y"
<submit_job xmlns="http://linkedprocess.org/2009/06/Farm#
vm_id="f472fb16...">
10.0
<submit_job/>
</iq>


44



45



46

General-Purpose: On the Nature of Jobs

• Jobs are executed synchronously where they are processed according to
a FIFO (first in, first out) queue.

• A job is a “chunk” of code in the language of the virtual machine. Jobs
can be as simple as setting a variable (e.g. i = 1 + 2;) to as complex
as a class definition or full program.

• Jobs can make use of the software packages (APIs) existing on the device.
For example, Groovy code can import Java classes made available by
the farm and instantiate them.

• If the expressions/code in a job violates the permissions of the virtual
machine, that job is rejected with a permission denied error.


47

General-Purpose: Terminating a Virtual Machine
• GET sent from a villein to virtual machine (indirectly through the farm)...
<terminate_vm xmlns="http://linkedprocess.org/2009/06/Farm#"
vm_id="f472fb16..." />
</iq>

• RESULT sent from the virtual machine to the villein (indirectly through
the farm)...
<iq from="test_countryside@...60KES71Y"
<terminate_vm xmlns="http://linkedprocess.org/2009/06/Farm#"
vm_id="f472fb16..."/>
</iq>


48



49


A terminated virtual machine releases all of its resources.


Outline
LoP
50






51

LoPSideD: A Java Implementation of the Linked Process
Protocol

• LoPSideD Farm: A farm that currently support JavaScript, Ruby, Python, and Groovy
virtual machines.
• LoPSideD Registry: A registry for advertising and locating farms.
• LoPSideD Villein API (Application Programming Interface): Classes to build villeins
that leverage a Linked Process cloud.
• LoPSideD Farm/Villein GUI (Graphical User Interface): A user interface for managing
a farm, for communicating with a farm, and generally useful for debugging (e.g. XMPP
packet sniﬃng mechanisms).

LoPSideD

52

LoPSideD Villein API

• Commands: Provides support to spawn/terminate virtual machines,
submit/ping/abort jobs, and manage bindings.

• Proxies: Provides a collection of proxy data structures that makes the
underlying XMPP protocol relatively invisible to the developer.

• Patterns: Provides support for various distributed computing patterns
such as asynchronous, synchronous, scatter/gather, etc.

• Demos: Provides a collection of simple demos such as a distributed
prime ﬁnding and distributed Web of Data analysis.


Outline
LoP
53






54

The Current State of Linked Process

• The Linked Process protocol speciﬁcation is nearly complete for
submission to the standards track of the XMPP Standards Foundation.
This means that the protocol that has been presented is still in a relatively
volatile state and various mechanics of the protocol may change through
this standards process.

• The LoPSideD implementation is nearly ready for a ﬁrst version release.

• An experiment demonstrating the use of Linked Process to distributed
computing on the Web of Data is currently being conducted.


55

The Future State of Linked Process

• Move the Linked Process speciﬁcation through the standards process
from experimental, to draft, and ultimately to standard status.

• Develop implementations of the Linked Process Villein API in other
languages (currently there are plans for a Ruby and Python port).

• Add more virtual machine species to the LoPSideD Farm implementation:
Scheme/Lisp, Tcl, PHP, SmallTalk, etc.

• Work with projects that are in need of the distributed computing solution
oﬀered by Linked Process.

• Work with more developers to expand the implementation base.


LoP
Acknowledgements
56

• Joshua Shinavier (Rensselaer Polytechnic Institute): codesigner of the
protocol and codeveloper of LoPSideD.

• Peter Neubauer (Neo Technology): evangelist and tester of the
LoPSideD codebase.

• Mick Thompson (Santa Fe Complex): provided the machines for the
deployment of the ﬁrst Linked Process cloud.

• Jack Moﬃtt and Peter Saint-Andre (XMPP Standards Foundation):
for support through the standards process.

Please visit Linked Process at http://linkedprocess.org.


General-Purpose, Internet-Scale Distributed Computing with Linked Process

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