WSO2 Stratos in contrast to Other Java PaaS Offerings

In the article "Java PaaS shootout" Michael J. Yuan provides a pretty nice comparison of Google AppEngine, Amazon Elastic Beanstalk, and CloudBees RUN@Cloud. Following table provides a summary of that while adding WSO2 Stratos to the comparison.

	App Engine	Amazon beanstalk	CloudBee's Run@Cloud	WSO2 Stratos
What is it?	Users can upload servlets. AppEngine hosts them and manage them.	Managed Tomcat Expensive	Tomcat, load balancer. Integrated with SVN. Can change source code and update all deployment aspects.	SOA platform as a service. Fully multi-tenant.
Java support	Yes, does not support some I/O and network operations	Full java	Full Java	Yes, but File access is limited
Outbound connections	Time out in 10 seconds	OK	OK	OK
Support for standard java Libs	Have problems when they use unsupported APIs	Yes	Yes	Yes (java security manager limits file accesses)
Performance and scalability	Auto scale, High scalability, but have bit high latency. Swapping the app out might slow down first request	Auto scale by creating EC2 instances	Can swap unused processes out of JVM. Can load balance multiple tomcats in the same EC2 instance	Can lazy load services and other artifacts. Auto scale (up down) by monitoring the load and creating new nodes. LB route the requests.
Storage	Support Big Table and Hosted MySQL.  However, search support in BigTable case is limited.  e.g.  Each query can only have 100 results.	Support RDS (relational) , SimpleDB (NoSQL) or can run with your own DB	Has managed MySQL databases and provide a console to manage them	Support Cassandra as a Service, managed MySQL, and HDFS.  Cassandra and HDFS support native multi-tenancy
Import/ export data	No (hard due to 30 sec limit)	Can write code to automate	Can write code to automate	Can write code to automate
Integration with others	Integrate well with other Google services	SQS, SES (email service), payment APIs	S3, SQS, SES etc.	With Google auth model and other WSO2 services. Also S3, SQS, SES etc.
Session handling	Store sessions to storage and handles them seamlessly	Only sticky sessions	Transparent session management	Only sticky sessions
Multi-tenancy	Yes	No	No	Yes

Also let me listout couple of key differentiators of WSO2 Stratos.

1. All these offerings support Web App Hosting as a Service. WSO2 Stratos supports that, but provides much more. In addition to Web App Hosting, it supports hosting Axis2 based services, Mediation, and Workflow hosting as a Service. It is real SOA platform as a Service, the only one to does that. 
2. It let you move your Axis2 based Web Services (.aar files) and workflows to the Cloud (to WSO2 Statos Live) without any change to them. If you have some Axis2 based services, chances are that you can upload them to WSO2 Stratos and it will just work. 
3. WSO2 Stratos provides real multi-tenancy support. That is different tenants will think that he has his own server, while actually all are served from one Java Server. In other words, Isolation is done at Java level, not at Virtualization level. That means it can provide greater sharing and provide "Pay as you go" and "Pay for what you use" better than VM based model. Only AppEngine does that out of other three PaaS offering. More details are in following papers. 
• A. Azeez, S. Perera, D. Gamage et al. (2010) Multi-tenant SOA Middleware for Cloud Computing, 458–465. In 2010 IEEE 3rd International Conference on Cloud Computing.
• A. Azeez and S. Perera et al., WSO2 Stratos: An Industrial Stack to Support Cloud Computing, IT: Methods and Applications of Informatics and Information Technology Journal, the special Issue on Cloud Computing, 2011.
• Milinda Pathirage, Srinath Perera, Sanjiva Weerawarana, Indika Kumara, A Multi-tenant Architecture for Business Process Execution, 9th International Conference on Web Services (ICWS), 2011