I attended this morning Mission Critical Enterprise Cloud Applications presented by a cheerful Eugene Ciurana; the presentation can be found on his site and Eugene managed to make it entertaining. I will not repeat here the contents of the presentation by I will try to capture its spirit and what made it particularly interesting. Eugene was not really after explaining what a Cloud is or why you should be adopting the Cloud in the enterprise, rather he focused on the classical usage of the Cloud in a hybrid architecture. In the hybrid case, part of your application is pushed to the cloud and part is hosted in your data center. The cloud could take over the data center but that’s not necessarily happening in the immediate/medium term future for reasons outlined here:
- SLA: As long as your SLA (Service Level Agreement) is reasonnable (say four nines as in 99.99% availablility) the cloud makes financial sense, beyond that the cloud becomes an expensive proposition
- Uptime is not the same thing as availability! The cloud may give you the impression of excellent up-time but your overall system availability may have dependencies on critical components that are better left (for the time being) to the data center
Two important questions to ask yourself before embarking on an adventure with Cloud vendor:
- What is the impact on business if the Cloud becomes unavailable?
- How can I/the vendor recover from a disaster
On the other hand cloud architectures are quite diversified: Eugene mentioned PaaS (Platform as a Service) , SaaS (Software as a Service), IaaS (Infrastructure as a Service) and finally Private Clouds (buily on top of VMWare, Eucalyptus, etc…)
He noted that event-based applications tend to scale better in the Cloud, but I think that this is a general statement that’s true even outside the Cloud. Event-based applications are simply more decoupled, the producer need not know anything about the consumer and vice-versa. He also noted that all Cloud implementations seem to have the following four characteristics:
- Quick deployment of pre-packaged applications (typically an image that gets deployed again and again)
- Commoditized H/W : consider Amazon EC2 and S3, Google App Engine, Rackspace
- Pay as you consume billing system -> brought an interesting point from a CFO pt of view: clouds become an operational expense
- Horizontal scalability is highly touted
The most interesting part of the presentation was a real-world study of a complex un-maintainable and un-scalable application that became hybridized with some functionality ported to the Cloud. The main feature of that re factoring effort was actually the introduction of an ESB (Mule) in the data-center to allow the services to scale without being actually tied to the physical databases: all JDBC calls are placed on the bus and memcache is used to alleviate performance issues. The (calculated) side effect was the ability to easily accomplish data mining by intercepting all calls going through the ESB. In the cloud a no-SQL datastore (such as S3) is used for write-once/consult type of access. healhy mix of Java and Jython was introduced to speed up development time. The final stack was Tomcat – Mule – Spring.
As for load balancing, it really depends on the vendor: Google App Engine uses a “mother-of-all-Servlets” for natural balancing while Amazon provides an explicit Elastic Load Balancer.
In conclusion it seemed that a hybrid solution represents the best compromise right now for most enterprises: Stateless/Computationally intensive services can safely reside in the cloud while your data can stay in your data center. As vendors start offering more legally-binding and stringent SLAs enterprises can start thinking of moving their infrastructure to the Cloud.
Computing Thoughts by Roger Rached 