Bài giảng Kiến trúc phần mềm - Bài 6: Middleware - Trần Minh Triết

CTT526 - Kiến trúc phần mềm
Middleware
PGS.TS. Trần Minh Triết
tmtriet@fit.hcmus.edu.vn
Trường Đại học Khoa Học Tự Nhiên
Khoa Công Nghệ Thông Tin
Bộ môn Công Nghệ Phần Mềm
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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
2
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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
3
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Middleware Classification
4
Business Process Orchestrators
Message Brokers
Application Servers
Transport Message-Oriented Middleware, Distributed Objects Systems
J2EE, CCM, .NET
BizTalk, WebSphere Message Broker, SonicMQ
BizTalk, TIBCO StaffWare, ActiveBPEL
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Outline
 CORBA
 Message-oriented middleware
 J2EE
 Message brokers
 Business process orchestrators
5
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CORBA
 Venerable distributed object technology
 Still widely used in telecomms, defense
 Many different implementations
6
Network
Client
Object Reference
request
Server
Servant
reply
client ORB server ORB
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CORBA Code Example
7
module ServerExample 
{ 
interface MyObject { string isAlive(); };
}; 
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(); 
CORBA IDL
Server
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
10
 Send (queue, message)
 Put message onto queue
 Receive (queue, message)
 Get message from queue
 No dependency on state of receiving 
application on message send
receivesend
queue
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Persistence
11
receivesend
queue
 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
12
MOM Server
Sending 
Applications
Senders
Message 
Handler Thread Pool
Sending 
Applications
Receivers
Peer-to-peer MOM technologies are the alternative design
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MOM Transactions
13
 B e g i n t r a n s a c t i o n 
. . . 
u p d a t e d a t a b a s e r e c o r d 
p u t m e s s a g e o n q u e u e 
. . . 
c o m m i t t r a n s a c t i o n 
B e g i n t r a n s a c t i o n 
. . . 
g e t m e s s a g e f r o m q u e u e 
u p d a t e d a t a b a s e r e c o r d 
. . . 
c o m m i t t r a n s a c t i o n 
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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
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receivesend
Request queue
Response queue
sendreceive
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Scaling MOM
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MOM Server
Senders Receivers
MOM Server
ApplicationQ
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
16
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Publish-Subscribe Messaging
 Extension of MOM to provide 1-to-N, N-to-1, and N-to-
N communications
 Messages are „published‟ to logical subjects or topics
 Subscribers receive all messages from subjects they 
subscribe to
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Pub Subject
Sub
Sub
Sub
Create/
Publish Register/
Subscribe
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Publish-Subscribe with Multicast
18
r v d 
r v d 
P u b l is h e r 
S u b s c r ib e r 
r v d 
S u b s c r ib e r 
r v d 
S u b s c r ib e r 
r v r d 
r v d 
S u b s c r ib e r 
r v d 
S u b s c r ib e r 
r v r d 
Based on 
TIBCO 
Rendezvous
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Performance
19
0
1 0 0
2 0 0
3 0 0
4 0 0
5 0 0
6 0 0
7 0 0
1 0 2 0 3 0 4 0 5 0
N o . O f S u b sc r i b e r s
M i l l i se c o n d s
M C 1
M C 2
Q B
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Subject/Topic Naming
20
Sydney
DevGroup SupportGroup
InformationInformation
work gossip work 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
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
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B ro w s e r -b a s e d c l ie n t
a p p lic a t io n s
(H T M L , a p p le ts ,
D H T M L /s c r ip t in g )
J a v a c l ie n t a p p l ic a t io n s
E R P s , C R M s ,
M a in f ra m e T P s y s te m s
S e rv le ts ,
J S P s
W e b
s e rv e r
H T T P
J a v a R M I
A p p l ic a t io n c o m p o n e n ts
E J B s
C lie n t t ie r B u s in e s s C o m p o n e n t t ie r E IS T ie rW e b T ie r
C o n ta in e r S e rv ic e s
C o m p o n e n ts
e g . J T S , J M S
R D B M S
J D B C
J C A
R M I
W in d o w s /C O M c l ie n t
a p p lic a t io n s
C A S C O M B r id g e , R M I o v e r I IO P
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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
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Application Server
EJB Container
Transaction
Service
Directory
Service
Security
Service
Thread Pool
Connection Pool
Persistence 
Lifecycle Management
EJB Pool
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Beans and State
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EJB Container
state
Stateless bean pool
Stateful beans 
state
state
state
state
state
state
EJB
Clients 
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Deployment Descriptors
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EntityStock.BrokerHome
db.entitystock.BrokerHome
db.entitystock.Broker
db.entitystock.BrokerBean
Stateless
Container
EntityStock.BrokerHome
Remote
*
Required
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J2EE – Some Thoughts
 Standards-based, multiple vendors, portable
 Good open source technology available
 Quality of implementations varies considerably
 Java only, wide platform support
 Performance is good, but varies between suppliers
 Scalable, fail over support through clustering
 Good integration with web technologies
 Supports various design patterns, flexible but more 
complex (e.g. stateful beans/scalability, entity beans)
 Standards evolving, need to monitor
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Message Brokers - Motivation
28
Web
Component
Legacy 
System #1
Legacy 
System #2
Legacy 
System #3
Legacy 
System #4
In-format
In-format In-format In-format In-format
Key:
Message = 
In-format
Message 
Transform Legacyformat
API
call
Queue
Read
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What if 
 the common In-format message format changes?
 any legacy system API changes?
 any of the transformations needs modifying? 
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Alternative Solution
 Transformations in 
broker
 Simplified 
endpoints
 Decouples Web 
and legacy 
components
30
Web
Component
Legacy 
System #1
Legacy 
System #2
Legacy 
System #3
Legacy 
System #4
In-format
L1-format L2-format L3-format L4-format
Key:
Message = 
Message
Broker
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Message Brokers
 Developed specifically for Enterprise Application 
Integration (EAI)
 Add new layers of functionality to MOM
 Message transformation
 Rules engine 
 Intelligent routing
 Adapters
 Typically (but not necessarily) built on top of a MOM 
layer
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Message Broker Features
 Message transformation – transform between 
different source/target formats
 Graphical message format definition and mapping tools
 High performance transformation engines
 Message format repositories
 Intelligent routing
 Route messages based on message content
 Rules Engine
 Scripting language, built-in functions
 Application programming environment
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Message Brokers
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Transformation
Routing
Rules Processing
Input Messages Output Messages
Hub and Spoke Architecture
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Example - WMQI
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BizTalk Mapping Tool
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Adapters
 An adapter is a component that resides between the 
message broker and the source/target systems
 Simplify complexity of end system interface through an 
abstraction layer
 Thin adapters - simple wrappers
 Thick adapters
 Programmable
 Abstract representation of services and meta-data
 Centralized adapters co-located with broker
 Distributed adapters execute in own process and may be 
located with source/target system
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Message Brokers – Some 
Thoughts
 Embeds transformations/routing in broker
 Can get complex
 Possible scaling issues
 Need to replicate brokers
 Failure handling
 Lightweight, rarely designed to recover from failure
 Often proprietary technology
 Good open source, standards-based like Mule now 
available
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Business Process Orchestration
 Commonly known as workflow
 Aim is to automate business processes which need 
to access data and business logic across disparate 
back-end applications
 Builds on EAI to ensure business processes are 
executed in the defined order using the required 
data
 Builds on middleware providing:
 Process execution engine
 Visual process definition tools
 Process monitoring tools
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Typical Scenario
 Business process automation
39
Customer
Purchasing
SAP
Customer
Receiving
Siebel
Sales desk
Shipping
Credit
Validation
Accounts
Payable
Accounts
Receivable
Oracle
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Example - BizTalk
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BPO Architecture
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Message Broker
Adapter Adapter Adapter
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BPEL
 Web Services standard for describing workflows
 Many design and execution tools
 Eg ActiveBPEL
 Version 2.0 is a significant improvement
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Integration Issues – Point-to-Point
 Point-to-Point evolution 
 Spaghetti architecture, hard to modify potentially (N2-N) 
interfaces
43
1 business process = 
4 interfaces
5 business processes = 
20 interfaces
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Broker Spaghetti
 No free lunch 
 Just relocates the spaghetti
44
message broker
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Enterprise Data Model
 Source sends message to target with common message format as 
payload.
 Target receives message and transforms common format into its own 
local data representation.
 2xN transformations, no broker needed
 Getting agreement is the tough bit 
45
Enterprise 
Data Model
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Summary
 Middleware:
 makes building complex, distributed, concurrent 
applications simpler.
 institutionalizes proven design practices by 
supporting them in off-the-shelf middleware 
technologies.
 Architect‟s job is to „mix n‟match‟ technologies to create 
appropriate solutions
 Analyze trade-offs
 Open-minded (no hammer/nail thinking)
 No good/evil, its just technology
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