I like the new phrase Cloud Tone, meaning uninterrupted application availability from the cloud. For those of us from the old school of OLTP, the importance of five nines (99.999% availability) is well-known. That suggests that the maximum outage of a system over one year will be less than 5.26 minutes. How do you guarantee that in the world of cloud computing? You have to find a balance between convenience and reliability. The mobile phone or smart phone is less reliable than the land line phone. The land line phones were paragons of five nines, but they do not give you flexibility of the smart phones. Hence users live with the annoyance of less availability for the convenience.
I read this interview with Urs Hölzle, Google’s infrastructure czar, whose current responsibilities include the design and operation of the servers, networks and data centers that power Google. It would be an understatement to say that he is amongst the folks who have shaped the modern web-infrastructure and cloud-related standards. Let me quote what he said about cloud computing – “As a person, you don’t have to worry about backups and viruses, Hölzle says. You don’t have to worry about changing machines, reconfiguring your machine or worry about installing software. On the cloud, there is no concept of scheduled downtime, because the cloud is supposed to work all the time. In other words, cloud-based computing helps you just actually do the work that your company was founded for, instead of focusing on the technology behind the tools that you’re using.”
Hölzle emphasizes that changes to application can cause interruptions and down time. Make no changes and the systems run well. The land line phone did not have any changes, hence the dial tone was always there. The current smartphones have so many applications which change all the time. He said that outages at Gmail need 30 people to manage. But the cloud infrastructure on which Gmail runs, also supports many other cloud apps. Google is a provider of PaaS (Platform as a Service) via its Google App. Engine platform. Microsoft is offering Azure Cloud platform for the same.
When web services were introduced few years back, we used the phrase “application dial tone” to describe their functions, since they provided the much-needed connections between heterogeneous applications. Cloud computing absorbs web services as one of many component pieces. It must address the reliability and availability aspects extremely well, so that the Cloud Tone (application availability) is available to users all the time.