The last couple of years, “Cloud Computing” replaced Web 2.0 as the new buzzword. You can read, hear and see everywhere the cloud is coming. To most developer, this is still the same old sh*t. If you have experience in developing distributed system then you should be fine, you say. Well not entirely true, the IT department wants to deploy on cheap cloud and therefore some restrictions now applies. I will list 5 things that I think all developers should know when working with cloud Platform as a Service provider such as Amazon Beanstalk or Google App Engine. This list also applies to IaaS architecture. Some of the points might be obvious to the more experienced, nevertheless, they need to be mentioned.
- Static objects
We all know the difference between instance variable (non-static) and class variable (static variable). We use static to tell the JVM that they should only be one instance of this variable (singleton). If the static variable is declared with the “final” keyword, this will not cause a problem in a distributed environment as the value will never change. The problem is when we expect the value of the variable to change. As in a cluster environment, GAE and Beanstalk run your application in multiple JVM. If a the value of your static variable has changed in JVM, it will not be propagated to the cluster therefore leading to inconsistencies. I recommend that you avoid static variable unless that set as “final” and their values are hard-coded so there is no way to change their values are runtime.
- Caching Objects
- Server-side Session
Note: Note, session data is always written synchronously to memcache. If a request tries to read the session data when memcache is not available (or the session data has been flushed), it will fail over to the datastore, which may not yet have the most recent session data. This means that asynchronous session persistence may cause your application to see stale session data. However, for most applications the latency benefit far outweighs the risk.
- Event-driven Execution
- JRE white list