Bài giảng Kiến trúc phần mềm: Middleware - PGS.TS. Trần Minh Triết

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Bộ môn Công Nghệ Phần Mềm

CTT526 - Kiến trúc phần mềm

Middleware
PGS.TS. Trần Minh Triết


Version 1.0

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 Nội dung của bài giảng sử dụng:
Session 4:
A Guide to Middleware Architectures and Technologies
trong bộ slide Software Architecture Essential
của GS. Ian Gorton
Software Engineering Institute
Carnegie Mellon University

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Introduction
 Middleware is the plumbing or wiring of IT

applications
 Provides applications with fundamental services for
distributed computing
 Insulates applications from underlying platform
(OS, DBMS, etc) APIs
 Lots of middleware exists
 Different purposes
 Different vendors
 Different standards and proprietary technologies

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Middleware Classification

Business Process Orchestrators

BizTalk, TIBCO StaffWare, ActiveBPEL

Message Brokers

BizTalk, WebSphere Message Broker, SonicMQ

Application Servers

Transport

J2EE, CCM, .NET

Message-Oriented Middleware, Distributed Objects Systems

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Outline






CORBA
Message-oriented middleware
J2EE
Message brokers
Business process orchestrators

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CORBA
 Venerable distributed object technology
 Still widely used in telecomms, defense
 Many different implementations

Client

Server

Object Reference
request

Servant
reply

client ORB

server ORB

Network

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CORBA Code Example
module ServerExample
{
interface MyObject {
};

Server

string isAlive();

};

CORBA IDL

class MyServant extends _MyObjectImplBase
{ public String isAlive() { return "\nLooks like it…\n";
}

ORB orb = ORB.init(args, null);
MyServant objRef = new MyServant();
orb.connect(objRef);
ORB orb = ORB.init(args, null);
// Lookup is a wrapper that actually access the CORBA Naming
// Service directory – details omitted for simplicity
MyServant servantRef = lookup(“Myservant”)String
reply = servantRef.isAlive();

}

Client

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CORBA – Some Thoughts
 Many associated services, eg

 Naming
 Notification
 Transactions
 Synchronous technology, client-server relatively tightly
coupled
 Remote calls can/will fail
 State management in server objects creates
„interesting‟ recovery issues

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Messaging - MOM
 Basic Message Oriented Middleware (MOM) provides
features like:
 Asynchronous communications between processes,
applications and systems
 Send-and-forget
 Delivering messages despite failures
 Transactional Messaging
 Deliver all messages in a transaction, or none
 Persistence
 Messages can be logged at the server and hence
survive server failure
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Basic Messaging


Send (queue, message)




Receive (queue, message)




Put message onto queue
Get message from queue

No dependency on state of receiving
application on message send
send

receive

queue

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Persistence

queue
send





receive

Receipt of message at queue implies
message is written to disk log
Removal of message from queue
deletes message from disk log
Trade-off performance versus reliability

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MOM Server

Receivers
Sending
Applications

Senders
Sending
Applications

Message
Handler Thread Pool
MOM Server

Peer-to-peer MOM technologies are the alternative design
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MOM Transactions
Begin

transaction

...

transaction

...

update
put

Begin

database

message

on

record
queue

...

get

message

update

from

database

queue
record

...

commit

transaction

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commit

transaction

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MOM Transactions
 Sender and receiver do *not* share a transaction
 Rollback on receiver does not affect the sender (already
committed)
 „Synchronous‟ operations are not atomic
 Request/response is 3 transactions not 1
 Put to request queue
 Get from request queue, put to response queue
 Get from response queue

Request queue
send

receive

send

receive

Response queue

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Scaling MOM
MOM Server
ApplicationQ

Senders

Receivers

MOM Server
ApplicationQ

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Messaging – Some thoughts





Highly attractive asynchronous technology
Supports loosely-coupled, dynamic applications
Scales well, high throughput possible

Many implementations, various qualities of service
 caveat emptor

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Publish-Subscribe Messaging
 Extension of MOM to provide 1-to-N, N-to-1, and N-toN communications
 Messages are „published‟ to logical subjects or topics
 Subscribers receive all messages from subjects they
subscribe to
Sub

Pub

Create/
Publish

Subject

Register/
Subscribe

Sub

Sub
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Publish-Subscribe with Multicast
S u b s c r ib e r

S u b s c r ib e r

rvd

rvd

rvrd

Based on
TIBCO
Rendezvous

P u b lis h e r

rvd

rvd

S u b s c r ib e r

rvrd

rvd

S u b s c r ib e r

rvd

S u b s c r ib e r

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Performance

M i l l i se c o n d s
700
600
500

M C1

400
M C2
300
QB

200
100
0
10

20

30

40

50
N o . O f S u b sc r i b e r s

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Subject/Topic Naming
Sydney

work

DevGroup

SupportGroup

Information

Information

gossip

Sydney

Sydney/DevGroup
Sydney/DevGroup/Information
Sydney/DevGroup/Information/work
Sydney/DevGroup/Information/gossip
Sydney/SupportGroup
Sydney/SupportGroup/Information
Sydney/SupportGroup/Information/work
Sydney/SupportGroup/Information/gossip

work

gossip

Sydney/*/Information
Sydney/DevGroup/*/*
Sydney/DevGroup/**

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Publish-Subscribe – Some
Thoughts
 Highly decoupled messaging style
 Publishers don‟t know about subscribers
 Subscribers don‟t know who is publishing
 Publishers and Subscribers can dynamically appear
and disappear
 Issues –

 Reliability
 Transactions
 Security
 Performance
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J2EE Overview
C lie n t t ie r

B u s in e s s C o m p o n e n t tie r

W e b T ie r

W eb

HTTP

s e rv e r

E I S T ie r

RMI
S e r v le t s ,

A p p lic a t io n c o m p o n e n t s

JSPs

E JB s

B r o w s e r - b a s e d c lie n t

JC A

a p p lic a tio n s
( H T M L , a p p le t s ,
D H T M L / s c r ip t in g )

ER Ps, C R M s,

Java R M I

M a in f r a m e T P s y s t e m s
C o n t a in e r S e r v ic e s

J a v a c lie n t a p p lic a tio n s

C o m p o n e n ts
eg. JTS , JM S

JD BC
RDBMS

C A S C O M B r id g e , R M I o v e r I I O P

W in d o w s / C O M c lie n t
a p p lic a tio n s

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J2EE Application Server
 In J2EE, the application server container provides the
execution environment for the J2EE-specific
components
 EJBs
 Message-driven beans
 Connectors

 Container provides additional services for hosted
components






Transactions
Security
Directory
Threading
Connection pooling
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EJB Container
Application Server
EJB Container
EJB Pool

Lifecycle Management

Transaction
Service

Directory
Service

Persistence

Connection Pool

Security
Service

Thread Pool

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Beans and State
state
EJB Container
Stateless bean pool

state

state
state

state

EJB
Clients

state
Stateful beans

state

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