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Things to think about whilearchitecting Azure solutions
Famous Last Words…
“It is a very humbling experience to make a multimillion-dollar mistake, but it is also very memorable….”
(Fred Brooks - “Mythical Man-Month” p.47)
So, What is Software Architecture exactly?
Software architecture is the fundamental organization of a system, embodied in its components, their relationships to each other and the environment, and the principles governing its design and evolution
Architecture forces
Architecture
Quality Attributes
Technology
Patterns & Anti-patterns
Principles
Community experience
Stakeholders
Architect
people
A “deliverable”
Produce
Key
Is an input
Constraints
Fallacies of distributed Computing
The Network is reliable
Latency is zero
Bandwidth is infinite
The Network is Secure
Topology doesn’t change
There is one administrator
Transport cost is zero
The Network is
homogenous
Dequeue/Delete pattern
The Network is reliable
Dequeue/Delete pattern
The Network is reliable
Still a problem If we crash here
Idempotencyf(x) = f(f(x))
Messages Process At Least Once
Web Role Worker Role
StorageQueue
LB
LB
Worker RoleWorker Role
Web Role Worker Role
1. Debit bank account $100 message2. Worker role reads message3. Balance debited $1004. Worker role is torn before message can be deleted5. 3 minutes later, message re-appears on queue6. Worker role reads message7. Balance debited $1008. Message deleted from queue9. Chaos ensues.....10. Customer calls bank.....
Balance = $1000Balance = $900Balance = $800
Solving the Idempotency Problem
Web Role Worker Role
StorageQueue
LB
LB
Worker RoleWorker Role
Web Role Worker Role
1. Debit bank account $100 message with transaction ID2. Worker role reads message. Checks transaction ID not present.3. Writes transaction ID with state ‘Started’ to ‘Replay Log’4. Balance debited $1005. Worker role is torn before message can be deleted6. 3 minutes later, message re-appears on queue7. Worker role reads message. Checks transaction ID. It is present in
state started.8. Compensating message written to another queue9. Message deleted from queue10. Compensatory message processed.Balance = $1000Balance = $900
Table
QueryQuery
Queue
Latency is zero
It might be infinite for all purposes but it costs…
Bandwidth is infinite
Authentication with ACS
Slide by Alik Levin
The Network is Secure
Service Bus• Provides secure messaging and connectivity across
different network topologies• Enables hybrid applications that span on-premises and
the cloud• Enables various communication protocols and patterns
for developers to engage in reliable messaging
Topology doesn’t change
Enabling hybrid applicationsDatacenter
LOB web
service
LOB app
Partner
Mobile Device
Enabling hybrid applicationsDatacenter
LOB web
service
LOB app
Partner
Mobile Device
SB
ACS
Enabling hybrid applicationsDatacenter
LOB web
service
LOB app
Partner
Mobile Device
SB
ACS
Enabling hybrid applicationsPartner
Mobile Device
Datacenter
LOB web
service
LOB app
SB
ACS
Enabling hybrid applicationsPartner
Mobile Device
Datacenter
LOB web
service
LOB app
SB
ACS
Electricity Power Grid
Demo
Don’t assume specific instances
Service Instance
NLB Driver
Worker Role
TCP/IP
Windows Kernel
Virtual NIC
Worker Role
TCP/IP
Windows Kernel
Virtual NIC
Virtual IP : 1.1.1.1
Virtual IP : 1.1.1.2Virtual IP : 1.1.1.3
Service InstanceIIS
Web Role
NIC Driver
TCP/IP
Windows Kernel
Virtual NIC
Virtual IP : 1.1.1.4
NIC Driver
TCP/IP
NIC Driver
TCP/IP
Inter-role communications
Reduced Headache on the one handNew challenges on the other
There is one administrator
Azure MMC Snap-in http://code.msdn.microsoft.com/windowsazuremmc
Cerebrata – Azure Diagnostics Managerhttp://www.cerebrata.com/Products/AzureDiagnosticsManager/Default.aspx
Transport cost is zero
Distribution cost in serialization, time on the wire, security
A lot of calls to fulfill a business function
Bring Data close to computation
It isn’t – but it’s abstractedunless of course you use Azure connect
The Network is
homogenous
Quickly connect on-premise computers with the cloud, no networking configuration required
Supports standard IP protocols; secured using end-to-end IPSec
Integrated with the Windows Azure Service Model; all role types supported
Deployment view
• Consider xsmall instances for development• Test if you can use less than medium for
production
Cost considerations
• You pay when you’re deployed (there is no “shelving”)– Shutdown doesn’t help– (keep CPUs running..)
2 Small instances cost the same as 1 medium instance
Compute Instance Size CPU Memory Instance Storage Cost per hour
Extra Small 1 GHz 768 MB 20 GB 0.05$
Small 1.6 GHz 1.75 GB 225 GB 0.12$
Medium 2 x 1.6 GHz 3.5 GB 490 GB 0.24$
Large 4 x 1.6 GHz 7 GB 1,000 GB 0.48$
Extra large 8 x 1.6 GHz 14 GB 2,040 GB 0.96$
2 instances can give you better availability
• Need to be on different fault and upgrade domains
I/O performance on smaller instances might be problematic
Compute Instance Size CPU Memory Instance Storage I/O Performance
Extra Small 1 GHz 768 MB 20 GB Low
Small 1.6 GHz 1.75 GB 225 GB Moderate
Medium 2 x 1.6 GHz 3.5 GB 490 GB High
Large 4 x 1.6 GHz 7 GB 1,000 GB High
Extra large 8 x 1.6 GHz 14 GB 2,040 GB High
You can control Azure from scripts and code (even dev fabric)
Testing
DEMO CLOUDOSCOPE ACCEPTANCE TESTS
Illustrations
• Slide 11 http://www.sxc.hu/photo/1201443• Slide http://www.sxc.hu/photo/1160486
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