[rlum]

I once heard you give an example of moving an application to the cloud only on days when predicted spikes occur. What about unexpected demands: how easy is it to automatically move the service from your servers to the cloud, on demand?

What other applications and scenarios would be great to move to the cloud?

[jravella2]

Additionally, does Azure support the notion of private and public clouds? Can applications be moved between the two or straddle them?

[sriramk]

What about unexpected demands: how easy is it to automatically move the service from your servers to the cloud, on demand?

That really depends on the kind of app. Provisioning new role instances and getting raw bits in place is the easy part. How to do a seamless transition, maintain data consistency, have a hybrid on-prem/cloud solution. handle current users - those are the tricky problems.

What other applications and scenarios would be great to move to the cloud?

I think anything that has variable resource usage - compute or storage - is great to move to the cloud. Variable usage means that you're always either under provisioned or scrambling for capacity - the cloud lets you deal with that

[sriramk]

Additionally, does Azure support the notion of private and public clouds? Can applications be moved between the two or straddle them?

That depends. What do you mean by 'private cloud'? . I'm asking because a lot of people are talking about different things when they say 'private cloud'.

[jravella2]

That depends. What do you mean by 'private cloud'? . I'm asking because a lot of people are talking about different things when they say 'private cloud'.

True enough, these terms are vague. To me a "private" cloud is one that runs on-premise behind the firewall. SO can I construct the application to run privately, then when capacity is tight, move the application onto Azure. Unless I misunderstand their technology, Eucalyptus is touting this feature for the Amazon platform.

I like the idea of developing, testing, and running locally then moving to the cloud when conditions dictate.

[sriramk]

True enough, these terms are vague. To me a "private" cloud is one that runs on-premise behind the firewall. SO can I construct the application to run privately, then when capacity is tight, move the application onto Azure. Unless I misunderstand their technology, Eucalyptus is touting this feature for the Amazon platform.

I like the idea of developing, testing, and running locally then moving to the cloud when conditions dictate.

Actually, the way you define it, that is closer to what a lot of folks would call 'cloudbursting'. There are many ways of doing it. One example on Windows Azure I talk about often is RiskMetrics. These guys do some serious math computation on Windows Azure. They have a hybrid on-prem/cloud model and they do a great job of moving data from on-prem when they need to do a job, spinning up instances, crunching on the data and then spinning down the instances.

The tricky issues with cloudbursting are with data. If you have an app that works on-prem, it probably has close ties to data located on-prem as well. If you're moving that to the cloud, you now have some options to consider. Do you reach back in on-prem (in which case, you have latency issues especially for interactive apps) or do you do some form of data replication?

As far as a private cloud with Windows Azure is concerned, check out the Windows Azure appliance which we just announced. That gives you an idea of the direction we're headed in