Hitchhiker's Guide to Software Architecture and Everything Else - by Michael Stal

Friday, February 12, 2010

Does Cloud Computing have an Architectural Impact?

Let’s suppose you have good reasons to leverage a Cloud infrastructure. Will this decision hava any impact on your architecture? The answer is quite easy: It depends :-)

  • If you just use virtualization to exactly simulate a physical environment like in Amazon EC2, then your applications will be oblivious to the Cloud infrastructure.
  • If you leverage SaaS (Software as a Service) like Salesforce.com then it’s a SEP (Somebody Else’s Problem).

However, if you use PaaS (Platform as a Service) or IaaS (Infrastructure as a Service) for your applications, then things definitely will change.

It is not so much the domain-specific logic that is influenced, but infrastructural and non-functional requirements will experience an impact.

  • In a Cloud environment different storage means are supported. In general, you’ll find Blobs and NoSQL databases. Designing the persistence infrastructure must take these issues into account unless you are still relying on a mainstream DBMS running somewhere in the Cloud.
  • For messaging Message Queues are available. Thus, message-oriented communication between Cloud-aware subsystems is a reasonable approach for connecting islands with each other. Often, SOA style communication protocols such as RESTful communication or SOAP/WS-* are supported. These protocols alone imply different architecture paradigms - designing the communication and distribution infrastructure can be a challenge.
  • All operational qualities such as performance, availability, scalability, fault-tolerance need to be implemented with the SLAs in mind the Cloud provider offers. If, for example, availability zones are supported in the Cloud you better plan how to leverage them according to your needs. In a public cloud security is even a more critical issue. You cannot naively trust the Cloud provider to keep your mission-critical data secret. Thus, you have to provide means like encryption almost everywhere. For performance reasons, you might want to consider the Cloud as a Grid such as in Apache HADOOP. But how can you partition your system in a suitable way. Is Mapreduce what you need or, otherwise, does your application require a different kind of approach? There are many different concurrency architectures like Master/Slave, Pipes & Filters, Concurrent Reactor that could be appropriate. In contrast to typical application development you are much more constrained when addressing these operational qualities, because many decisions the Clound infrastructure has already made for you. It is YOU who needs to integrate with the Cloud, not vice-versa.
  • Developmental qualities such as modularity, modifiability, maintainability can be hard to achieve in such an environment. First of all, you should introduce some kind of governance approach. Secondly, you need to modularize in such a way that governance issues live in harmony with the kind of modularization propagated by the Cloud, in particular by the PaaS APIs. For command & control purposes you need to think about how to administer the Cloud applications. There might be 3rd party products for this purpose. It, however, might also be the case you have to implement your own tooling.
  • If, for some reason, you need to use different cloud infrastructures, interoperability might be a big issue given that today’s approaches almost inevitably lead to vendor-lock-in.

Not always, you will be able to start with a green field project, but rather need to deploy an existing application ecosystem or parts of it to the Cloud infrastructure. Migration is not straightforward as we already saw earlier. You may need to combine reengineering and refactoring activities for this purpose.

This posting describes only the tip of the iceberg. I hope, people will develop some best practices (patterns) for how to leverage existing Cloud platforms. I’d be rather sceptical if someone would come up with such patterns soon. You surely remember, patterns must be independently used in three different applications to make them patterns. I cannot imagine, we already obtained that much experience in practice.

So, if you are going to design for Amazon EC2, Google Web Engine or Microsoft Azure don’t forget: Mind the Cloud!


Post a Comment

<< Home