CS330 September 14 and 16, 2005 Enterprise Architectures Johannes - - PDF document
CS330 September 14 and 16, 2005 Enterprise Architectures Johannes Gehrke johannes@cs.cornell.edu http://www.cs.cornell.edu/johannes (Some of the slides are courtesy of Gustavo Alonso, Fabio Casati, Harumi Kuno, Vijay Machiraju and Ethan
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Client is any user or program that wants to perform an operation over the
system through a presentation layer The application logic determines what the system actually does. It takes care of enforcing the business rules and establish the business processes. The application logic can take many forms: programs, constraints, business processes, etc. The resource manager deals with the
retrieval) of the data necessary to support the application logic. This is typically a database but it can also be a text retrieval system or any other data management system providing querying capabilities and persistence. Client Application Logic Resource Manager Presentation layer Business rules Business objects Client Server Database Client Business processes Persistent storage 6
between two parts of the system.
system: more opportunities for distribution and parallelism. This allows encapsulation, component based design, reuse.
sessions (connections) need to be maintained, more coordination is necessary. The system becomes more complex to monitor and manage.
context switches and intermediate steps to go through before one gets to the data. Performance suffers considerably.
flexibility of modular design with the performance demands of real applications. Once a layer is established, it tends to migrate down and merge with lower layers.
There is no problem in system design that cannot be solved by adding a level of indirection. There is no performance problem that cannot be solved by removing a level of indirection.
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top-down design PL-A PL-B PL-C AL-A AL-B AL-D AL-C RM-1 RM-2 top-down architecture RM-1 RM-2 AL-A AL-D AL-C AL-B PL-A PL-B PL-C
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presentation layer resource management layer application logic layer client i n f
m a t i
s y s t e m
and client platforms
formats and protocols for the selected clients and protocols
necessary to deliver the contents and formats needed at the presentation layer
and data organization needed to implement the application logic top-down design
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basic components already exist. These are stand alone systems which need to be integrated into new systems.
cease to work as stand alone
continue running at the same time as new applications.
because the underlying systems already exist and cannot be easily replaced.
area are related to middleware, the intermediate layer used to provide a common interface, bridge heterogeneity, and cope with distribution.
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bottom-up design PL-A PL-B PL-C AL-A AL-B AL-D AL-C b
t
p a r c h i t e c t u r e AL-A AL-D AL-C AL-B PL-A PL-B PL-C
wrapper wrapper wrapper wrapper wrapper wrapper
legacy application legacy application
legacy system legacy system legacy system
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presentation layer resource management layer application logic layer client i n f
m a t i
s y s t e m
and client platforms
and the functionality they offer
and integrate their functionality into a consistent interface
application logic so that it can be used with the required access channels and client protocols bottom-up design
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application logic and resource manager are built as a monolithic entity.
advantages:
control flow (everything happens within the system),
controlling resources is easier,
separation between layers.
Server
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powerful, it was possible to move the presentation layer to the
advantages:
(Application Program Interface). An interface to invoke the system from the outside. It also allows designers to think about federating the systems into a single system.
This greatly helps with performance since there are no client connections/sessions to maintain.
Server
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service)
resource management layer s e r v e r service interface service interface service interface service interface server’s API service service service service
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tier),
ignoring presentation issues
point of view
Connect to two systems, a client needs two presentation layers.
since they are all competing for the same resources.
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with heterogeneous systems is shifted to the client.
responsible for knowing where things are, how to get to them, and how to ensure consistency
design, portability, code reuse, performance since the client capacity is limited, etc.).
with 2-tier Server A Server B
know about each other
(increasingly fat clients)
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indirection between clients and
business logic encompassing all underlying systems.
system:
by reducing the number of interfaces,
the underlying systems,
system functionality and high level application logic, and
accessing them, and gathering results.
Middleware or global application logic clients Local resource managers Local application logic
Server A Server B
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usually 2 tier),
very difficult to provide, and
(some forms of it).
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External clients connecting logic control user logic internal clients 2 tier systems Resource managers wrappers
Resource manager 2 tier system middleware system External client
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from connecting several three tier systems to each
layer led to the notion of “application servers”, which was used to refer to middleware platforms supporting access through the Web client resource management layer application logic layer i n f
m a t i
s y s t e m middleware presentation layer Web server Web browser HTML filter
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INTERNET FIREWALL LAN Web server cluster LAN, gateways LAN internal clients LAN middleware application logic resource management layer database server
LAN middleware application logic
additional resource management layers
LAN Wrappers and gateways
file server application
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systems use blocking calls Synchronous interaction requires both parties to be “on-line”: the caller makes a request, the receiver gets the request, processes the request, sends a response, the caller receives the response.
response comes back. but the interaction requires both client and server to be “alive” at the same time
Call Receive Response Answer idle time
failures
react to failures
complex interactions
client server
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between the caller and the receiver.
active at the same time
systems often resort to connection pooling to optimize resource utilization
connections
needed
requires a context for each call and a context management system for all incoming calls. request() do with answer receive process return session duration request() do with answer receive process return Context is lost Needs to be restarted!!
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the context is lost.
1, nothing has happened
but before 2 (receiver crashes), then the request is lost
but before 3, side effects may cause inconsistencies
but before 4, the response is lost but the action has been performed (do it again?)
took place may not be easy. If there is a chain of invocations the failure can occur anywhere along the chain. request() do with answer receive process return 1 2 3 4 request() do with answer timeout try again do with answer receive process return 1 2 3 receive process return 2’ 3’
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load balancing ASYNCHRONOUS INTERACTION
interaction, the caller sends a message that gets stored somewhere until the receiver reads it and sends a response. The response is sent in a similar manner
take place in two forms:
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excellent complement to synchronous interactions:
the code for making a request can be in a different module (even a different machine!) than the code for dealing with the response
distribution modes and it also helps to handle communication sessions in a more abstract way
implement complex interactions between heterogeneous systems do with answer do with answer request() request() receive process return queue queue
to request the whole document again (more later…)
another connection to the server.
<title>Sample Homepage</title> <img src="/images/oreilly_mast.gif"> <h1>Welcome</h2>This is the web page of ...
head request.
version.
application development: Other functionality has to be built on top
need to be encoded in every HTTP request and response!
lecture)
< HTML> < HEAD> < /HEAD> < BODY> < h1> Barns and Nobble Internet Bookstore< /h1> Our inventory: < h3> Science< /h3> < b> The Character of Physical Law< /b> < UL> < LI> Author: Richard Feynman< /LI> < LI> Published 1980< /LI> < LI> Hardcover< /LI> < /UL>
<h3>Fiction</h3> <b>Waiting for the Mahatma</b> <UL> <LI>Author: R.K. Narayan</LI> <LI>Published 1981</LI> </UL> <b>The English Teacher</b> <UL> <LI>Author: R.K. Narayan</LI> <LI>Published 1980</LI> <LI>Paperback</LI> </UL> </BODY> </HTML>
* Actually, you could check the log files for IP addresses, but Internet proxies and NAT are a problem.
Give me the home page! Here’s the home page plus a cookie. Now, give me the news page (cookie is sent automatically) I’ve seen you before… Here’s the news page.