soa systems design
DESCRIPTION
Service Oriented Architecture Systems Design Patterns.TRANSCRIPT
| 25-06-2012 | Alexander van Trijffel
18-06-2012
Your business technologists. Powering progress © Confidential
Service Oriented Architecture Systems Design
Alexander van Trijffel
| 25-06-2012 | Alexander van Trijffel 2
Agenda▶ The network▶ Coupling ▶ Messaging▶ Reliability▶ Services▶ Service
decomposition
| 25-06-2012 | Alexander van Trijffel
Connectivity – The network matters
▶ Common assumptions made by developers and architects in distributed systems
• The network is reliable• Latency isn’t a problem• Bandwidth isn’t a problem• The network is secure• The topology won’t change• The administrator will know what to do• Transport cost isn’t a problem• The network is homogeneous
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| 25-06-2012 | Alexander van Trijffel
“The 8 fallacies of distributed computing”
1. The network is reliable2. Latency isn’t a problem3. Bandwidth isn’t a problem4. The network is secure5. The topology won’t change6. The administrator will know what to do7. Transport cost isn’t a problem8. The network is homogeneous
4
Deutsch 94
Gosling 97
| 25-06-2012 | Alexander van Trijffel
Coupling
▶ What is coupling?
– A measure of dependencies
– If X depends on Y, there is coupling between them
– 2 kinds of coupling:
– Afferent (Ca) - Who depends on you
– Efferent (Ce) - On who do you depend
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Loose coupling at the systems level
▶ Attempt to minimize afferent and efferent coupling
▶ 3 Different aspects of coupling for systems:– Platform– Temporal– Spatial
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Coupling Aspect: Platform
▶ Also known as “Interoperability”
▶ Using protocols only available on one platform– Remoting– Enterprise Services/COM+– Datasets over Web Services
▶ One of the 4 Tenets of Service Orientation:– “Share contract and schema, not class or type”
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Coupling Aspect: Temporal
Service A
Synchronous Call
Waiting Working
Return
Service B
The processing time of Service B affects that of A
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Coupling aspect: Spatial
Service A
Service B
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Coupling aspect: Spatial
Service A
Service B
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Coupling aspect: Spatial
Service A
Service B
Service B
?Can communication
automatically continue?
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Coupling solutions
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Coupling Aspect #1: Platform
▶ XML on the wire.
▶ XSD (schema) describing XML structure
▶ Use standards based transfer protocol like http
▶ Standards based description of message flow– WSDL
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Coupling Aspect #2: Temporal - 1
Service A Service B
Customer GetCustomerInfo(id)
Calling thread iswaiting for theresult
MakeCustomerPreferred(id)
Save customer as preferred
Bad. Resources are held while waiting.
| 25-06-2012 | Alexander van Trijffel
Coupling Aspect #2: Temporal - 2
Resources are held while waiting. Increased load on service B per consumer (impacted by polling interval)
Service A Service B
YieldCustomerInfo(id)MakeCustomerPreferred(id)
Spawn polling thread
Got data?
Data ready
Got data?
Got data?
Save customer as preferred
Data ready butnot passed toconsumer
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Coupling Aspect #2: Temporal - final
Good. By separating (in time) the inter-service communication and the request handling
Service A Service B
Publish updated customer infoStore data
MakeCustomerPreferred(id)
Save customer as preferred
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Coupling Aspect #3: Spatial
▶ Application level code should not need to know where cooperating services are on the network
▶ Delegate communications to “something else”, let’s call it an “agent” for now.– myAgent.Send(message);
▶ But if the application code doesn’t tell the agent which logical destination to send the message to, how would the agent know?
▶ If there was a direct mapping from message type to logical destination, then specifying the type of message being sent/published would be enough
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Message Type = Logical Destination
▶ AddCustomerMessage: – Sent by clients to one logical server– Multiple physical servers behind a load balancer if required
▶ OrderCancelledEventMessage:– Published by one logical server
▶ Strongly-typed messages simplify routing
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Messaging
▶ Asynchronous: One-way, fire & forget messages
▶ Why messaging?
▶ Reduces coupling– Use XML for platform coupling– Use asynchronous messaging for temporal coupling
▶ Reduces Afferent and Efferent coupling while increasing autonomy
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Performance – RPC vs Messaging
▶ With RPC, threads are allocated with load– With messaging, threads are independent– Difference based on blocking nature of communication
▶ Memory, DB locks, held longer with RPC
Throughput
Load
RPC
Messaging
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Reliability
▶ When servers crash
▶ When databases are down
▶ When deadlocks occur in the database
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When Servers Crash
DBApp[HTTP] $$ Order
TxCall 1 of 3
Call 2 of 3
Critical Windows Patch
Rollback
Where’s the order!?
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When Deadlocks Happen
TxApp[HTTP] $$ Order
DBCall 1 of 3
Deadlock
ExceptionWrite to log A B
Call 2 of 3
Where’s the order!?
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Securing client requests with Messaging
TxQ$$ Order
App
Receive
DBCall 1 of 3
Rollback
Call 2 of 3
Rollback
The order is back in the queue
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Calling Web Services
A B C D
WSDB
[HTTP] Invoke
$$ Order
Deadlock
Rollback
Not Rolled back
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MessagingGateway
A B C D
WS
Msg
DB
$$ Order
[HTTP] Invoke
The message won’t be sent if there’s a failure
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Durable Messaging
Server
Client
MSMQ
MSMQIncomingOutgoing
Outgoing Incoming
Store and Forward
adds resilience
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Message types
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Standard message handling
▶ Problem is that service layers get too large▶ Difficult for multiple developers to collaborate▶ Difficult to reuse logging, authorization, etc
Customer Service
void ChangeAddress(Guid id, Address a);
void MakePreferred(Guid id);
void ChangeCredit(Guid id, Credit c);
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Exploit strongly-typed messages
IMessagewhere T : IMessage
IHandleMessages<T>void Handle(T message);
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Represent methods as messages IMessage
ChangeAddress
MakePreferred
ChangeCredit
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Handling Logic Separated
IHandleMessages<T>void Handle(T message);
H1: IHandleMessages<ChangeAddress>
H2: IHandleMessages<MakePreferred>
H3: IHandleMessages<ChangeCredit>
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Multiple handlers per message
H1: IHandleMessages<ChangeAddress>
H4: IHandleMessages<ChangeAddressV2>
Authorization: IHandleMessages<IMessage>
▶ Dispatch based on type polymorphism▶ Allows for pipeline of handler invocation▶ As side effect less merge change conflicts
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Demo
▶ Sending a and receiving a message using the bus
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Messaging patterns
▶ Return Address▶ Correlated Request/Response▶ Publish Subscribe
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Return Address Pattern – Send / Reply
2 Channels: one for requests, one for responses
Return Address
Target Service
Return Address
Some time in the future
Initiating Service
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Correlated Request/Response
Target Service
Some time in the future
Initiating Service
Ticket (guid)
Ticket (guid)
In the header of the response message, there is a correlation id equal to the request message id
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Publish / Subscribe
Service A Service B
Publish updated customer infoStore data
MakeCustomerPreferred(id)
Save customer as preferred
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Publisher
Subscriber
Subscribe
Subscriber
Subscriber
Subscriber
Subscriber
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Publisher
Subscriber
Subscriber
Subscriber
Subscriber
SubscriberMyEvent
MyEvent
MyEvent
MyEvent
MyEvent
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Demo
▶ Publishing an event
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What is a service?
▶ A service is the technical authority for a specific business capability.
▶ All data and business rules reside within the service.
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What a service is NOT
▶ A service that has only functionality is a function, not a service.– Like check if order is valid
▶ A service that has only data is a database, not a service.– Like [create, read, update, delete] entity
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Technical properties of a service
▶ A service may have multiple end points
▶ A service may communicate over multiple protocols and transports
▶ A service is responsible for its own availability and scalability
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Service deployments
▶ Many services can be deployed to the same box
▶ Many services can be deployed in the same app
▶ Many services can cooperate in a workflow
▶ Many services can be mashed up in the same page
| 25-06-2012 | Alexander van Trijffel
Service Examples
Subscribe to Customer Status Updated
Publish
Customer Status Updated
Save status locally
Subscribe to Product Pricing Updated
Publish
Product Pricing Updated
Save pricing locally
Place Order
Publish Order Accepted
Sales
Marketing
Customer care
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Which service owns this page?
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Which service owns this page?
None
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Same page composition
Server
Product Catalog
Pricing
Inventory
Cross Sell
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Amazon.com checkout workflow
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Which service owns this flow?
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Which service owns this flow?
None
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Workflow composition
Shipping
Billing
SalesBilling
BillingShipping
Shipping
Marketing
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Autonomous Components
▶ The large-scale business capability that a service provides can be further broken down
▶ A service is composed of one or more Autonomous Components
▶ An AC takes responsibility for a specific set of message types in the service
▶ Autonomous Components are the unit of deployment in SOA
▶ An AC uses the bus to communicate with other ACs.
Is independently deployable, has its own endpoint
| 25-06-2012 | Alexander van Trijffel
Flexibility in deployment
▶ Any number of autonomous components (ACs) can be deployed to a single machine
▶ Or even a single process
▶ Or have a single AC deployed on each machine
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Bus TopologyApp
Bus.dll
App
Bus.dll
App
Bus.dll
App
Bus.dll
App
Bus.dll
App
Bus.dll
App
Bus.dll
App
Bus.dll
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Scalability
▶ Since each autonomous component maintains its state in the database of its service
▶ We can have a number of servers each running an instance of the same autonomous component
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Scaling out an AC Autonomous Component
Distributor ACI
ACI ACI
Ready
Autonomous Component Instance
on each machine
| 25-06-2012 | Alexander van Trijffel
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Atos, the Atos logo, Atos Consulting, Atos Worldline, Atos Sphere, Atos Cloud and Atos WorldGridare registered trademarks of Atos SA. June 2011© 2011 Atos. Confidential information owned by Atos, to be used by the recipient only. This document, or any part of it, may not be reproduced, copied, circulated and/or distributed nor quoted without prior written approval from Atos.
Your business technologists. Powering progress © ConfidentialYour business technologists. Powering progress © Confidential
www.atos.net
Atos, the Atos logo, Atos Consulting, Atos Worldline, Atos Sphere, Atos Cloud and Atos Worldgridare registered trademarks of Atos SA. July 2011© 2011 Atos. Confidential information owned by Atos, to be used by the recipient only. This document, or any part of it, may not be reproduced, copied, circulated and/or distributed nor quoted without prior written approval from Atos.
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Alexander van Trijffel