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this is the slides from the talk i gave at DevGeekWeek2014 further details are in my blog: http://blogs.microsoft.co.il/iblogger/2014/06/25/devgeekweek-2014-slides-and-demos/
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Azure Cloud Patterns
About Me
• Software architect, consultant and instructor• Software Engineering Lecturer @ Ruppin Academic Center• Technology addict• .NET and Native Windows Programming
@[email protected]://www.TamirDresher.com.
Cloud Patterns
http://en.wikipedia.org/wiki/List_of_cloud_types
Agenda
• What are Cloud Patterns
• Queue Centric
• Poison Messages
• Retry Logic
• Circuit Breaker
• Cache Aside
What are Cloud Patterns
• Architectural Patterns:“A design pattern in architecture and computer science is a formal way of documenting a solution to a design problem in a particular field of expertise”(http://en.wikipedia.org/wiki/Architectural_patterns)
Meet The ProblemDevGeek Coffee Shop
DevGeek Coffee Shop
• DevGeek Coffee is a well known and established coffee shop
• In business for 20 years
• Lately, with the increasing competition, sales are dropping
• Lets Help!
DevGeek Coffee Shop - Operations
coffee
DevGeek Coffee Shop - Operations
coffee#!$@
What does this has to do with software?
• Cashier == Server
• Basically, this is a scalability issue
• Running in the cloud (potentially) makes scaling problem appear faster
Scale Up
• Add More Resources to a Node
• Faster cashier– Better CPU to the server– More Memory
• Faster Coffee machine– Use a better algorithm/service
Everything has a limit
MoneyMoneyCPUCPU
MEMMEMBANDWIDTHBANDWIDTH
StorageStorage
Scale out
• Add More Nodes– More Cashiers
• Load Distribution– Round Robin– Performance– Other (location, expertise, etc)
Azure Traffic Manager
Meet The Problem 2DevGeek Coffee Shop
DevGeek Coffee Shop – The clients complaints
• Long standing
• Sometimes orders gets lost
• Sometimes the line is so long that the workers close the doors
DevGeek Coffee Shop – Latency and throughput
• Latency is a time interval between the stimulation and response– Time between ordering and receiving the coffee
• Throughput is the number of requests that can be served per unit time
DevGeek Coffee Shop – Aroma model
coffee.
Message Centric
Web Sites worker role::
worker roleweb role
Message Centric – Load Leveling
::
Request Received at variable rate
Messages Processed at consistent rate
Message Centric – Resilency
::
X
X
Message Centric – Delayed Processing
::
Azure Queuing Options
• Azure Storage Queues– Simple, Reliable, Persistent Queue– Max 200TB and 7 days TTL per message
• Azure Service Bus– Broader capabilities: publish/subscribe, remoting,
integration patterns– Max 80GB and unlimited TTL per message
http://msdn.microsoft.com/en-us/library/hh767287.aspx
Azure Service Bus – Queueing
Service Bus Messaging - Queue
• Two parts: 1.key/value properties2.binary message body.
• Example: a sales application sends message properties:
• *Seller="Ava" • *Amount=10000. • body : The sale's signed contract scanned image
Producer ConsumerDemo
C2
21
21
11
11
Removing Poison Messages
11
11
21
21334
0
40
Producers Consumers
30
30
2. GetMessage(Q, 30 s) msg 2
1. GetMessage(Q, 30 s) msg 1
11
11
21
21
10
10
20
20
P2
P1
C1
C2
P2
P1
C1
Removing Poison Messages
340
40
Producers Consumers
11
11
21
21
2. GetMessage(Q, 30 s) msg 23. C2 consumed msg 24. DeleteMessage(Q, msg 2)7. GetMessage(Q, 30 s) msg 1
1. GetMessage(Q, 30 s) msg 15. C1 crashed
11
11
21
21
6. msg1 visible 30 s after Dequeue30
30
12
1211
1112
12
C2
P2
P1
C1
Removing Poison Messages
340
40
Producers Consumers
12
12
2. Dequeue(Q, 30 sec) msg 23. C2 consumed msg 24. Delete(Q, msg 2)7. Dequeue(Q, 30 sec) msg 18. C2 crashed
1. Dequeue(Q, 30 sec) msg 15. C1 crashed10. C1 restarted11. Dequeue(Q, 30 sec) msg 112. DeliveryCount > 213. msg1.DeadLetter
12
12
6. msg1 visible 30s after Dequeue9. msg1 visible 30s after Dequeue
30
30
13
1312
1213
13
Service Bus Messaging – Dead letters
• the name of the sub-queue is [queueName]/$DeadLetterQueue
• The path can be obtained using the FormatDeadLetterPath method of the QueueClient
• Can be consumed by any other consumer and check the messages, log them etc.
Priority Queue
• The queue may hold message with different priorities (3-High, 1-Low)
Web Sites worker role::
worker roleweb role
:
Priority Queue
Application
Priority Queue
Application
Meet The Problem 3DevGeek Coffee Shop
DevGeek Coffee Shop – The clients complaints
1. Sometimes the soy milk ran out
2. the barista calls to the storeroom
3. The line is busy
4. The barista move to next order
5. Customer receive an order cancellation
Transient Faults
• “Transient fault is a fault that is no longer present if power is disconnected for a short time and then restored.” (http://en.wikipedia.org/wiki/Transient_fault#Transient_fault)
• Many faults in connectivity to cloud are transient by nature
• Commonly occur when connecting to service or database
Retry Pattern
• If at first you don’t succeed, try try again (William Edward Hickson)
• Retry Logic– Linear – every fixed amount of time– Exponential – if the server is heavy-used (throttling)
we don’t want to flood it immediate….1 sec….5 seconds….etc.
– Other
Operation With Basic Retry int currentRetry = 0; while (currentRetry < MaxRetries) { try { // Calling external service. await TransientOperationAsync(); } catch (Exception ex) { currentRetry++; // Check if the exception thrown was a transient exception if (!IsTransient(ex)) { // If this is not a transient error // or we should not retry re-throw the exception. throw; } } await Task.Delay(TimeBetweenRetries); }
Retry Pattern – Solutions
• Azure Storage IRetryPolicy
• Azure Service Bus RetryPolicy
IRetryPolicy noRetryPolicy = new NoRetry();BlobRequestOptions requestOptions = new BlobRequestOptions(){ RetryPolicy = noRetryPolicy,};
MessagingFactory factory = MessagingFactory.Create();factory.RetryPolicy = RetryExponential.Default; factory.RetryPolicy = RetryPolicy.NoRetry;
The Transient Fault Handling Application Blockvar retryPolicy = new Incremental(5, TimeSpan.FromSeconds(1), TimeSpan.FromSeconds(2));
retryPolicy.Retrying += (sender, args) => {Trace.WriteLine(args.LastException, "Information");
};
try { retryPolicy.ExecuteAction(() => {
TranisentErrorOperation(); });}catch (Exception) { // All the retries failed.}
http://msdn.microsoft.com/en-us/library/hh680934(v=pandp.50).aspx
Circuit Breaker
Retry Logic – Not Always Not all The time
• Baristas keeps retrying/failing – Time Consuming
• Maybe we can call someone else?
• The remote service still might get flooded
• If a failure is not transient, we wish that next attempts fail immediately
Circuit Breaker
• Circuit Breaker pattern prevent repeatedly trying to execute an operation that is likely to fail
• continue without waiting for the fault to be rectified
• Prevents wasting valuable resources because of the wait
Circuit Breaker
• The Circuit Breaker is a proxy
• Monitor the number of recent failures
• Decide if to proceed or do something else– Throw exception– Try different destination
Circuit Breaker States
Closed Open
Success
Fail [threshold reached]
Half Open
Retry Timeout
Fail
Success
Fail [under threshold]
Cache Aside
Deja vu
• We fetch the same data
• We run the same calculation
• We query the same service
Cache Aside
Azure Caching
• Azure Managed Cache
• Azure Redis Cache
• In-Role Cache
In Role Cache – co-located
In Role Cache - Dedicated
InRole Cache
Summery
• What are Cloud Patterns
• Queue Centric
• Poison Messages
• Retry Logic
• Circuit Breaker
• Cache Aside
References
• P&P Cloud Design Patterns - http://msdn.microsoft.com/en-us/library/dn568099.aspx
• http://cloudpatterns.org/• Cloud Architecture Patterns
Images References
1. http://en.wikipedia.org/wiki/List_of_cloud_types
2. http://www.freedigitalphotos.net/images/Emotions_g96-Arms_Up_Character_Shows_Shock_And_Surprise_p142355.html
3. http://www.freedigitalphotos.net/images/Hot_drinks_g184-Coffee_In_White_Cup_p96634.html