DISTRIBUTED PROCESS IMPLEMENTAION

BHAVIN KANSARA

OBJECTIVE

Logical Model Of Local And Remote Processes Three application scenarios

• Remote Service• Remote Execution• Process Migration

Mobile agent Process migration vs. mobile agents

Logical Model Of Local And Remote Processes

Local Process Remote Process

Stub Process Stub Process

CLIENT SERVER

THREE APPLICATION SCENARIOS

Depending on how request messages are interpreted,

there are three significant application scenarios :

Remote Service Remote Execution Process Migration

REMOTE SERVICE

Its primary application : resource sharing in distributed systems.

request message for remote service can be generated at three different software levels.

• As remote procedure calls at the language level• As remote commands at the operating system level• As interpretive messages at the application level

Remote Procedure Calls At The Language Level

At language level for remote service requests

Most suitable model : RPC

It is service oriented and provides both access and location transparency

At the operating system level

There are some frequently used commands that need to invoke remote objects. These commands can be built in as part of the command shell and recognized by the local operating system

Remote Commands At The Operating System Level

Remote commands are limited only to shell commands. The concept can be generalized to process messages.

user Want to send message Remote host

Some user-defined operations at remote hostinvoke

Stub process at Server site has capability of

-- Interpreting messages sent from client stub -- invoking respective operations

Rules application communication protocol

Based on the content of message

Interpretive Messages At The Application Level

Remote operations

Initiated byRemote procedure calls remote commands interpretive messages

Constrained to

Services that are supported at the remote host

Primary implementation issues

I/O redirection security

Client stub

server stub

copies Client process’ standard input to the remote command

Standard output and error of the remote command to client process

copies

Access to remote resources required authorization

REMOTE EXECUTION

• Remote operation initiated by client is created by the client

• message sent from client to server is client program to be executed at the server

Means generating process at remote host

Selected host

System with specific resources for resource sharing

Remote Service

System with purpose of load sharing

Remote Execution

Implementation issueLoad sharing algorithm location independence system heterogeneity protection and security

Load sharing algorithm

Process serverResponsible for

Maintaining load information negotiating remote host invoking remote operation creating stub processes for linking client& server

Remote execution Initiated

Implicitly – local process serverexplicitly – process

Relationship of process Parent/child or disjoint

Load sharing algorithm

Practical implementation

Each process server maintain list of registered hosts

First step is to select remote host

Client process serverindicate

Resource requirement to process server at remote site

If authenticated and its resource request can be met

Server grants permission for remote execution

LOCATION INDEPENDANCE

Process created by remote execution require

Coordination to accomplish common task

So, it is necessary to support logical view for the processes

Each remote process is represented by an agent process at the originating host

SYSTEM HETEROGENEITY

If remote execution is invoked on heterogeneous host

It is necessary to recompile the program

Overhead may be too high

Solution

Use canonical machine-independent intermediate language for program execution.

PROTECTION AND SECURITY

Remote execution powerful

Foreign code image can be Trojan horse

Solution

• Accept only remote execution in source or intermediate codes

• Language used to describe a remote execution could be restricted to exclude potential problems

• Run-time checking of parameters and stack overflow is also necessary to protect the integrity of the remote hosts

PROCESS MIGRATION

Process P1::::

Executionsuspended

Source Site Destination Site

ExecutionResumed

::::

Process P1

Transfer of control

Time

Freezingtime

LINK REDIRECTION

Transfer ofaddress space

Sourcenode

Destinationnode

SuspendedMigrationdecision

resumed

Freezingtime

Transfer ofaddress space

Sourcenode

Destinationnode

Suspended

Migrationdecision

resumed

Freezingtime

Total Freezing Pretransferring

Merits: easy implementationDemerits: long delay time

Merits: freezing time reduceDemerits: total time extended

MESSAGE FORWARDING

Three types of messages:

1. received when the process execution is stopped on the sourcenode and has not restarted on the destination node

2. received on the source node after the execution started ondestination node

3. sent to the migrant process after it started execution ondestination node

MESSAGE FORWARDING

Sender

Origin

Dest 1

Dest 2

Receiver

Migrate

Migrate again

Resend

Resend again

Sender

Origin

Dest 1

Dest 2

Receiver

Migrate

Migrate again

Resending messages Ask origin site

SendSend

Forward

messages of type 1 and 2 are either dropped or negatively ack-ed, the sender is notified and it needs to locate the migrant process

origin node keeps the info on the current location of the process created there, all messages are sent to origin whichforwards them to migrant process

MESSAGE FORWARDING

Sender

Origin

Dest 1

Dest 2

Receiver

Migrate

Migrate again

Link traversal

Link

Link

Send

Forward

Forward

Send

messages of type 1 are queued and sent to destination node as part of migration procedure

link is left on source node to redirectmessages of type 2 and 3, link contains the system-wideunique id of a process and its last known location

MESSAGE FORWARDING

Sender

Origin

Dest 1

Dest 2

Receiver

Migrate

Migrate again

Link Update

Send

New location

Send

New location

Send

Current location

during the transfer the source node sends the notification (link update) of the transfer to all the nodes to which the process communicates:

messages of type 1 and 2 are forwarded by the source node

messages of type 3 are sent directly to the destination node

MOBILE AGENTS

• it is composition of computer software and data which is able to move from one computer to another autonomously and continue its execution on the destination computer.

• It refers to a process that can transport its state from one environment to another, with its data intact

• Mobile agents can decide when and where to move next

• When a mobile agent decides to move, it saves its own state and transports this saved state to next host and resume execution from the saved state.

Common applications include:• Resource availability, discovery, monitoring • Information retrieval • Network management • Dynamic software deployment

Process migration vs. mobile agents

Process Migration Mobile Agents

Navigational Autonomy

Migration decision is made by system.

Agents decide where and where to go

Code Execution Programs are fully compiled and executed in native mode.

Most agents are coded in Java and are interpreted by their execution engine.

Strong/Weak Migration

Execution is resumed where it has been suspended.

Java-based agents resume their execution from the top of a given method.

I/O State Long-term I/Os are forwarded to processes migrated to the destination.

Agents relinquish I/O connections every time they depart for their next destination.

REFERENCES

Distributed operating system and algorithms Randy chow, Theodore johnson

A Framework for Process Migration in Software DSM Environments ieeexplore.ieee.org/iel5/6662/17807/00823407.pdf …. ( 2000 )

Presentation on Parallel & Distributed Computing courses.washington.edu/css434/slides/Migration.ppt

Mobile agent - Wikipedia, the free encyclopedia en.wikipedia.org/wiki/Mobile_agent