1. Building Scalable Resilient Websites in Azure
Steve Spencer Solution Architect, Liberis, Nottingham Microsoft Azure MVP @sdspencer

2. Agenda
What is resilient and scalable?
Why do we care?
Building Scalability
Building Resilience
How can Microsoft Azure help?
Tips and Tricks

3. What is resilient and scalable?
“Resilience is the ability to provide and maintain an acceptable level of service in the face of faults and challenges to normal operation”
“Scalability is the capability of a system, network, or process to handle a growing amount of work, or its potential to be enlarged in order to accommodate that growth”

4. Why do we care?
We want to provide a good service
We want the web site to be quick
We want the web site to work even when things go wrong
Our site makes us money, so we don’t want things to go wrong
We want to make a good impression

5. Building Scalability Scale Up Scale Out
Add More resources to an existing server e.g. Cores, RAM, Disk space
Easier to scale existing applications
Limited by cost and physics
Scale Out
Add more of the same servers
More difficult to scale existing applications
More cost effective for large scale
Likely to need infrastructure and application changes

6. Building Scalability
Web Site
Web Services
Business Logic
Data Access

7. Building Scalability Web Site Web Site Web Site Web Site Web Site
Web Services
Web Services
Web Services
Web Services
Business Logic
Business Logic
Data Access
Data Access

8. Scaling out – Application Issues
File access
Files written to local disk not accessible to other nodes
Can use file share or data store (e.g. document database like Mongo or Redis)
Session State
In memory session not available to other nodes
Caching
In memory cache needs distributing to all nodes
Shared Resource contention
E.g. Writing to the same file
Bottlenecks
E.g. Database

9. Scale out – Infrastructure Issues
Routing
Load balancing
File Sharing
Security, Access etc
Accessing Shared Resources (e.g. Database)
IP whitelisting, Firewalls etc
Bandwidth
Latency
Legacy Hardware/Software e.g. Mainframe
Configuration Management

10. Assume things will go wrong and deal with it
Building Resilience
Handle Failure
Disaster Recovery
Transient failures
Cyber attacks
Upgrading/Maintenance
Assume things will go wrong and deal with it
Understand bottlenecks and points of failure
What happens if something fails?
What do you want to happen?

11. Handling Failure – Multiple Instances
Same DC
Different DC
Helps mitigate DR, Cyber Attacks & Upgrading/Maintenance
Has the same issues as Scale Out

12. Handling Failure – Retry Logic
Distributed systems fail
Accessing things over a network is unreliable
Retry calls to network resources if a failure occurs
Add a limit to the number of times to retry
Increase the timeout between retries
Randomise
Helps mitigate against transient failures

13. Handling Failure – UI
Don’t just fail in the UI
Display a maintenance screen for planned outages
Show as much information as possible but highlight time critical information as being out of date
Use caching in the UI

14. If stale data not acceptable then show message for that data
Handling Failure – UI
If stale data not acceptable then show message for that data
Allow users to do as much as possible
Use queuing for updates
Cache locally
Make dynamic pages static so not always pulling data from data store
Make xml file containing the data. Only useful for data that doesn’t change often
e.g. Account history – mainly static data for each account that updates over time

15. Single Points of failure Single points of load
Bottlenecks
Single Points of failure
Single points of load
Normally difficult to scale
Types
Legacy components
Databases
Logging
Understand your application & identify potential bottlenecks
Load/performance test

16. How can Microsoft Azure help?
Cloud based not on premises
Multi-tenant environment
Windows and Linux
Any Language (.Net, Java, Node.JS, Python etc)
Collection of services to build applications
Different hosting models
Infrastructure as a Service (IaaS) e.g. Virtual Machines
Platforms as a Service (PaaS) e.g. WebApps, Service Fabric
Software as a Service (SaaS) e.g. Office 365 (Exchange, Lync, SharePoint), CRM 365
Container as a Service (CaaS) e.g. Azure Container Service (currently Linux only)
Scale In and Out – Pay for what you use (Opex not Capex)

17. Issues moving to the cloud
Legacy components
Can they run in the cloud? Does the cloud support the legacy OS?
Access to on premises resources
E.g. Mainframe access, CRM, ERP, Legacy component etc
File access
Can you use file shares in the cloud?
Security
Cloud is in the public domain so need to make sure things are secure
Don’t use 

18. How can Microsoft Azure help?
Multi-region
Geo-redundancy
Hosting
Azure websites
Virtual Machines
Service Fabric
Data
SQL DB & Elastic DB
Redis Cache
DocumentDB
Blob & CDN

19. How can Microsoft Azure help?
Networking & Integration
Traffic Manager
Service Bus
Hybrid Connections
Security
Azure AD (AAD)
AAD B2C
MFA
Key Vault
Tools
TFS Online
Load Testing
Dev/Test Labs

20. Three instances of data across a single data centre
Blobs
Scalable File storage
Three instances of data across a single data centre
Automatically load balances
Can be configured as Geo-Redundant with Read Only Access
Can create SMB Share
Access
Use Blob API (Private Blob)
Open public URL (Public Blob)
Public URL with SAS (Private Blob with Shared Access Signature)

21. Databases Standard SQL Elastic Database Scale Up
Threat Detection and Alerts
Automatic Tuning
Point in Time Restore
High On-Prem SQL Compatibility
Geo-Replication
Elastic Database
Scale Out
Sharding

22. Azure Websites Platform as a Service
You only need to manage your application
Alerts and Monitoring
Manual or Auto scale
Web jobs
Good for backend processing
Can be scaled out separately
Multiple deployment slots
Staging
A-B testing
VIP swap
Easy to automate deployment
Supports Hybrid Connections

23. Traffic Manager DNS based routing Across data centres
Can handle a single total datacentre failure
Can access any service with public access
Non-Microsoft Clouds
Own hosting
Can be configured for
Priority (DR)
Weighted (Round Robin) – Can be used for gradual upgrade
Performance (Fastest)

24. CDN
Content Delivery Network
Integrates with Azure Blob Storage
Global Coverage – More than just Azure Data centre
Caches Blobs local to calling client
Integrates with Blobs with different URL

25. Tips and Tricks – No Code Changes
Autoscale
Move load from website e.g. use blobs and cdn
User Redis for caching
ASP.NET Session State Provider for Azure Redis Cache (config change + nuget)
Load test and measure performance
Helps identify bottlenecks
Provides baseline data to help understand limits for scaling

26. Tips and Tricks – Code Changes
Don’t wait, use Async
Use Queues
Load balance back end
More resilient
Use Geo-Redundant Read Only data
Database Sharding or Partitioning
E.g. use multiple databases

28. Summary
Applications & Infrastructure will need to change for scale out and resilience
Things fail in a networked environment so be prepared
Know your application and understand the bottlenecks
Azure offers support for Scaling and Resilience
Make use of the tools and services available to make your website scalable and resilient

29. Thank you for listening. Any Questions?
@sdspencer