REQUEST/REPLY COMMUNICATION

BHAVIN KANSARA

OBJECTIVE

•Request/Reply Communication

•RPC ( Remote Procedure Call )

RPC Operation

Issues Associated with RPC

parameter passing

binding

compilation

failure handling

security

Sun’s secure RPC

GridRPC

REQUEST/REPLY COMMUNICATION

Most widely used request/reply communication model is Remote Procedure Call (RPC)

WHAT IS RPC

Process on Procedure P

machine M1 on machine M2Calls

M1 is suspended

M2 executes P

When M2 returns, controls back to M1

•Neither message passing nor I/O at all are visible to the programmer

This method is known as Remote Procedure Call (RPC)

RPC: STUB COMPONENTS

-- Program subsystems used by client or server to initiate an RPC request

-- The stubs are responsible for managing all details of the remote communication between client and server• Client calls client stub residing on local

machine ,responsible for packing the call and its parameters into a message format

• On server side, a server stub unpacks the message into call request

RPC OPERATION

ISSUES ASSOCIATED WITH RPC Parameter passing Binding Compilation Failure handling Security

PARAMETER PASSING Functions in an application that runs in a single process may collaborate via parameters and/or global variables

Passing parameters is typically the only way that RPC-based clients and servers share information

Parameter-passing has following possible modes: IN: pass info from caller to callee OUT: callee writes a value in the caller IN/OUT: caller tells callee value of var, which may be updated by callee

Parameter passing methods Call by value

Call by reference Call by copy/restore

PARAMETER PASSING Call by Value

• IN Mode

• simple to handle

• Value passed to procedure is copied to local variable

• can’t have an effect on caller variable

Call by reference• IN/OUT mode

• Much harder to handle

• Pass pointer address

• Same memory location is referred Call by copy/restore

• IN/OUT mode

• Call by value + call by reference

• Call by value at entry of procedure and restricts the call by reference to

the exit of the call• Results are copied back to the calling procedure at the completion of the called procedure

BINDING

When server machine is unknown, the client will need to locate the server machine by contacting directory server to locate address of server system

Manages mapping between program

number and port number

BINDING

Server starts registers its communication endpoint by sending request to port mapper that contains server’s program, version number and port number

BINDING

Client process contact port mapper to obtain handler for accessing server with specific program and version number. This is done by RPC run-time library routine create.

BINDING

The port mapper returns the port number of the server to the client system after verifying the program and version number.

BINDING

Client system builds client handle for the client process for subsequent use in the remote procedure call.

Binding process establish socket connection between client and server

RPC COMPILATION

The compilation of RPC requires three major components in the RPC package

• An interface specification file

• RPC generator which takes the interface specification file as input and produces the client and server stub procedure source code as output

• A run-time library for the supporting execution of RPC

RPC COMPILATION

RPC COMPILATION

RPC COMPILATION

RPC FAILURE HANDLING

Failures can be of three types

• Lost message

• Server crash

• Client crash

RPC FAILURE HANDLINGLost Message

Sever is allocated and request message has been sent

Message may delay or lost

Lost message are eventually detected by time out or no response form server

Retransmission

Request was not lost but delayed server will receive two request

SOLUTION

--- Request can be executed any number of times with same effect

--- using sequence numbers

RPC FAILURE HANDLINGServer CrashThree possible assumptions for the RPC semantics in the presence of failure :" Exactly once?

• Server crashes before request arrives• server crashes before reply• server crashes after reply, but reply dropped

" At most once?• If server crashes, can’t know if request was done

" At least once?• Keep retrying across crashes, but may be done multiple times

Most desirable Exactly once difficult to achieve

SOLUCTION

--- Problem lies in the loss of cache table

--- Use at least once semantics and to log the cache table

--- When the server recovers it reloads cache table from log

RPC FAILURE HANDLINGClient Crash

Before server completes the client request, the server has an orphan computation and its reply is undeliverable.

No easy way for the server to detect the disappearance of clients except by using a time-out or by waiting for the failed client to reboot

Orphan computations consume server resources

Can be eliminated by :

By Client : upon reboot of failed client

By Server : the server occasionally tries to locate the owners of its remote operations and abort those whose owners can not be found

By Expiration : each remote operation is given a maximum lifetime

SECURITY

• RPC is a form of remote execution that allows programs or commands to be executed on other systems. But it also opens doors for attacks from unfriendly remote users

Mutual authentication

--- identities of clients and server are verified --- Request Message Client server --- Reply message server client

Message integrity, confidentiality, and originality

--- request/reply messages have not been tampered with (integrity), their contents are not revealed ( confidentiality) , and the same message has not appeared more than once ( originality )

Truly generated by Intended for

SUN’S SECURE RPC

GRIDRPC• One of grid programming models

Supports remote procedure calls (RPCs) on the Grid

• Standardized at GridRPCStandardizing only minimal set of APIsHigher-level features can be built on topProviding several reference implementations

• Usage scenariosRemote library calls for executing compute-intensive tasksExecuting large scale task-parallel processing

NINF-G SYSTEM (2000..)• Reference implementation of GridRPC• Constructed on top of Globus

Globus is introduced in many sites•No more security halls are required in introducing Ninf-G2•Ninfied applications can be executed on many sites

Globus provides primitive functions/tools for grid computing•Concentrating on the development of RPC specific functions•Easy to use other tools on Globus

Ninf-G2 hides complicated mechanisms of Globus•Grid applications/middleware can be easily constructed

GRID APPLICATIONS USING NINF-G

• Chemical simulationReplica Exchange Monte Carlo

Surveying potential energy of moleculesTime Dependent Density Functional Theory

Simulating time evolution of electron system in molecules

• Optimization problemVehicle Routing

Searching optimal route for delivery

• Weather simulationS-model

Forecasting global weather change

REFERENCES•Distributed operating system and algorithms Randy chow, Theodore johnson

•Remote procedure call - Wikipedia, the free encyclopedia en.wikipedia.org/wiki/Remote_procedure_call

•Sun RPC www.cdk4.net/additional/rmi/Ed2/SunRPC.pdf

•GridRPC: A Remote Procedure Call API for Grid Computing www.cs.umd.edu/class/spring2004/cmsc818s/Readings/GridRPC-GGF-APM-jul02.pdf

•Grid technology research center http://projects.gtrc.aist.go.jp/en/ http://www.ngp.org.sg/events/AIST-NGO_MOU/NINF.pdf