At
Neudesic we do a great deal of Windows Azure consulting and development. Here are the best practices we've identified from our field experience:
1. Validate your approach in the cloud early on
2. Run a minimum of 2 server instances for high availability
3. SOA best practices generally apply in the cloud.
4. SOAP is out, REST is in.
5. Be as stateless as possible.
6. Co-locate code and data as much as possible.
7. Take advantage of data center affinity.
8. Retry calls to Windows Azure services, SQL Azure databases, and your own web services before failing.
9. Use separation of concerns to isolate cloud/enterprise differences.
10. Get as current as possible before migrating to azure.
11. Migrate applications one tier at a time.
1. Validate your approach in the cloud early on. Once you have a tentative solution design, test the viability of your design in the cloud early in your project to validate its viability. Don’t wait until the end of your project to find out if your approach will work. Your solution in the cloud may reveal very different dynamics and performance from the enterprise, and you may encounter issues with supported features and deployment. Waiting until the last minute to test viability in the cloud is dangerous.
2. Run a minimum of 2 server instances for high availability. When hosting in Windows Azure, consider 2 as the minimum server farm size. If you only run 1 server, you will experience periods of unavailability as patches or updates are applied. When you have 2 more servers in a farm, patches and updates are sequenced to prevent downtime. The Windows Azure SLA is only guaranteed when there are at least 2 servers in a farm.
3. SOA best practices apply to the cloud. The principles of Service-Oriented Architecture apply equally well to the cloud as they do in the enterprise:
Connect programs with loose coupling
Define explicit boundaries
Use interoperable standards
Define coarse-grained contracts and avoid chatty interfaces
Favor stateless services
4. SOAP is out, REST is in. REST is part of “how we do things in the cloud”. The best way to write effective cloud software is to be in line with its philosophies and preferred protocols. SOAP does of course play a role in key areas such as federated security but for application developers it’s about REST these days. Take advantage of related technologies like WCF RIA Services.
5. Be as stateless as possible. Farms for web applications, web services, and workers can be adjusted at any time to larger or smaller sizes. The best way to code wherever possible is to avoid session state. If you must have session state, implement it in a way that doesn’t rely on server affinity.
6. Co-Locate code and data as much as possible. Whether your code is in the cloud or in the enterprise, it’s best if code and the data it accesses are near each other. Avoid unnecessary traffic between cloud and enterprise.
7. Take advantage of data center affinity. Since many cloud solutions involve multiple projects (hosting, storage, database, communication, security) use the Affinity Group feature of the Azure management portal to ensure a related set of projects reside in the same data center.
8. Retry calls to Windows Azure services, SQL Azure databases, and your own web services before failing. Any HTTP call can fail, and you should expect calls to the cloud will fail or time out at times. Your calling code should attempt a limited number of retries before failing. This applies to your own web services, to Windows Azure services (storage, communication, security), and to SQL Azure databases.
9. Use separation of concerns to isolate cloud/enterprise differences. Use common interfaces and dual service implementations to provide equivalent cloud and on-premise functionality to your apps. If you’re writing applications that need to work in the cloud as well as on-premise, you’ll have to implement some things slightly differently—for example, accessing a local file server vs. accessing blob storage in the cloud. A great way to do this is to define a common service interface (with functions like GetFile, PutFile) and have two implementations, one for on-premise and one for in the cloud.
10. Get as Current As Possible Before Migrating to Azure. The more current you are on Microsoft technologies in your enterprise app before migration, the easier the migration will be. A case in point is SQL Server to SQL Azure. If you’re not on SQL Server 2008 yet, you should get compatible with that before migrating to SQL Azure. Otherwise you’ll have twice the number of issues in getting the database migrated and it will be less clear what’s an Azure issue vs. a SQL Server version issue.
11. Migrate applications one tier at a time. Since most solutions have multiple tiers, a migration to the cloud can be approached one tier at a time—keeping the solution running all the while. This is analogous to keeping a patient alive through a series of surgeries. By focusing on one software layer at a time, you carve a complex job into a series of smaller more focused tasks. It’s best to migrate database first, then web services, then front end.
