PaaS (Platform-as-a-Service) is a type of cloud service in which the provider delivers not only on-demand hardware and operating-system services, but also application platforms and solution stacks. For developers, PaaS dramatically reduces the headache and overhead of IT deployments, and makes applications more easily scalable by providing resources to the application on-demand.

The Java platform is well suited for PaaS since the JVM, the application server, and deployment archives (e.g., WARs and EARs) provide natural isolations for Java applications, allowing multiple developers to deploy applications in the same infrastructure. However, for the past several years, most PaaS offerings were around platforms such as Ruby and Python, whilst Google App Engine was a lone PaaS provider for Java developers. Fortunately, that is starting to change.

In the past year or so, several commercial providers have entered the Java PaaS space. It makes sense since the estimated 10 million Java developers almost certainly represent one of the biggest developer groups in the world. In this article, we will try to compare those PaaS offerings from the developers’ point of view. Specifically, our comparison methodology is to compare the features of each offering in 4 areas:

Support for technology platforms and stacks.

Support for developer productivity and development processes.

Performance and scalability.

Pricing and other business concerns.

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In this article, we will compare the following Java PaaS offerings (in alphabetical order).

Amazon Elastic Beanstalk is Amazon’s Java PaaS offering built on their EC2 cloud. It provides managed Tomcat instances running on EC2, complete with load balancers and on-demand provisioning capabilities for scaling. It integrates with the rest of Amazon Web Services to provide access to managed relational databases (RDS), big data stores (SimpleDB), message queues, email, and other services.

is Amazon’s Java PaaS offering built on their EC2 cloud. It provides managed Tomcat instances running on EC2, complete with load balancers and on-demand provisioning capabilities for scaling. It integrates with the rest of Amazon Web Services to provide access to managed relational databases (RDS), big data stores (SimpleDB), message queues, email, and other services. CloudBees is a VC-based startup that is run by JBoss and Sun veterans, and recently raised $14M in two rounds of financing. It may be a new name, but its influence is fast growing in this space. CloudBees brings several unique features into the Java PaaS scene, in particular continuous integration - a complete development / deployment cycle management in the cloud. In addition, like Heroku, the company includes a market place for 3 rd party plugins and services.

is a VC-based startup that is run by JBoss and Sun veterans, and recently raised $14M in two rounds of financing. It may be a new name, but its influence is fast growing in this space. CloudBees brings several unique features into the Java PaaS scene, in particular continuous integration - a complete development / deployment cycle management in the cloud. In addition, like Heroku, the company includes a market place for 3 party plugins and services. Cloud Foundry is an Open Source initiative from VMware. VMware software powers virtualized data centers, which is the basis of most PaaS offerings. VMware is also the home of Spring Framework, a very popular platform stack in enterprise Java. A unique feature of Cloud Foundry is that it does not have to be a hosted PaaS at all. You can download its code and host a PaaS yourself! In that sense, it is both a hosting platform and a hosted PaaS service.

is an Open Source initiative from VMware. VMware software powers virtualized data centers, which is the basis of most PaaS offerings. VMware is also the home of Spring Framework, a very popular platform stack in enterprise Java. A unique feature of Cloud Foundry is that it does not have to be a hosted PaaS at all. You can download its code and host a PaaS yourself! In that sense, it is both a hosting platform and a hosted PaaS service. Google App Engine for Java is perhaps the oldest (and most mature) Java PaaS offerings on the market. It has an ambitious goal of linear scalability, and it is not afraid of making drastic changes to the Java platform itself.

is perhaps the oldest (and most mature) Java PaaS offerings on the market. It has an ambitious goal of linear scalability, and it is not afraid of making drastic changes to the Java platform itself. Heroku for Java is the latest offering from PaaS power house Heroku, which has a deep heritage in the Ruby community.

is the latest offering from PaaS power house Heroku, which has a deep heritage in the Ruby community. Red Hat OpenShift is Red Hat’s experimental offering in PaaS. Red Hat’s JBoss Application Server (AS) is amongst the most popular Java application servers, and the OpenShift service provides comprehensive JBoss AS support.

Supported Technology Platforms and Stacks

One of the most important attributes of a Java PaaS provider is the technology platform and stack it supports. After all, the technology platform is what distinguishes Java PaaS from all other PaaS offerings. Yet, during the long evolution of the Java platform, there have been many competing technology stacks on the platform. For the Java PaaS vendor, I believe that supporting as many different technology stacks as possible is very important.

In this category OpenShift and CloudBees support the widest variety of technologies, from a simple servlet container (typically Tomcat) to full Java EE 6 Web Profile support (JBoss AS 7). The Java PaaS pioneer, Google App Engine, is now lagging behind most newcomers in terms of standards support. Google App Engine does not support the full Java SE platform, and hence offers poor support for many popular frameworks. Google App Engine also requires the user to program to its own network and persistence APIs, as opposed to supporting the open standard, resulting in applications that are very hard to port. Similarly, Heroku for Java requires the application to wrap around its own Jetty instance, breaking the more traditional Java EE application deployment model.

The Cloud Foundry project supports the Tomcat container. But its application development and deployment are heavily optimized for the Spring framework, creating an semi external dependency. Cloud Foundry is well suited to applications based on the Spring framework since its parent company, VMware, is also the owner of Spring. In addition the platform supports message queuing using RabbitMQ and based on the AMQP standard. But its support for other Java frameworks such as the Java EE is weak.

Amazon Beanstalk CloudBees Cloud Foundry Google App Engine Heroku for Java OpenShift Tomcat Yes Yes Yes No No Yes Java SE Yes Yes Yes No Yes Yes Java EE No Yes No No No Yes Support standard Java libraries Yes Yes Yes No Yes Yes File system access Yes Yes Yes No Yes Yes Thread access Yes Yes Yes No Yes Yes Outbound network connections Yes Yes Yes Limited Yes Yes MySQL RDS Yes Yes Paid plan Yes Yes Commercial relational databases RDS External External No External External Big Data support SimpleDB External External BigTable External External Deploy without special frameworks Yes Yes No No Yes Yes Friendly to migrate existing apps Yes Yes No No No Yes Portability of apps High High Moderate Low Low High Production ready? Yes Yes Beta Yes Beta Beta

Support for Developer Productivity and Development Processes

A key value of the PaaS is that it makes life easier for application developers, as it removes the overhead for application and resource management. So, developer friendliness and tools integration is an important consideration in our evaluation.

In this category CloudBees is a clear winner. It is not only a PaaS runtime environment, but also an integrated build and test environment. Developers can make use of the Jenkins service to have CloudBees automatically and continuously check out, build, test, and report code in the repository. This continuous integration process has been adopted by many large teams as a key component of their software development process. However, build server management is often time consuming and painstaking work for the QA team. CloudBees takes out this pain, and make the process much more transparent for developers. Recently, Red Hat OpenShift has made progress catching up to CloudBees in this space by supporting Maven and Jenkins integration.

Amazon Beanstalk, OpenShift, and Google App Engine all provide developer tools, SDKs, and IDE plugins that are consistent with other Java-based tools in the market.

Cloud Foundry and Heroku for Java, however, provide tools that are more suited for Ruby developers than for Java developers. Having used their tools, I suspect that many Java developers will take some time to get used to their conventions and terminologies. In addition Cloud Foundry currently suffers from poor documentation. For instance, much of its documentation is in the form of video tutorials. While video tutorials are great to get developer started, they lack the depth required for deploying serious applications, or for developers who wish to go beyond the scripted scenarios. Their official documentation of getting started guides were dated in 2007, despite significant changes their platform has gone through in the last couple of years. More recent documentation is available - for example here - but isn't as eay to find as it should be.

Another important point is that, while Cloud Foundry allows developers to setup their own cloud environments, to deploy Micro Cloud is significantly more involved than to just install an SDK. That is a barrier that makes Cloud Foundry difficult for many developers.

Amazon Beanstalk CloudBees Cloud Foundry Google App Engine Heroku for Java OpenShift IDE tools Yes Yes Yes Yes No Yes Command line tools Yes Yes Yes Yes Yes Yes Web-based console Yes Yes No Yes No Yes Testing on dev machine Easy Easy Hard Hard Yes Easy Build without non-standard dependency Yes Yes No No No Yes Source control integration No Yes Yes No No Partly Integrated build No Yes No No No Yes Integrated testing No Yes No No No No Access to logs via web No Yes Yes Yes Yes Yes Third party developer / testing services No Yes No No No No API access Yes Yes No No Yes No Documentation Good Good Poor Good Good Good

Performance and Scalability

One of the most important features of PaaS is the platform’s ability to auto-scale. That is to increase and decrease server capacity based on real-time demand of traffic. It requires the platform provider to load balance requests across a number of servers, monitor the load on each server, and to spin up new servers as needed.

All PaaS providers support auto-scaling to some extent. But auto-scaling is harder than it looks. For starters, the Java EE application must be configured to access a centralized external database as opposed to a database server co-hosted on the same server. The programming paradigm and tools for all PaaS providers need to force the developer to do that.

An even bigger problem is HTTP sessions. In Java application servers, the session state of HTTP sessions are managed in-memory by default. To build applications that can be load balanced across different servers, the developer must do one of the following:

Configure the load balancer to support “sticky session”. That is for the load balancer to inspect the session ID of all incoming requests, and always direct requests in the same session to the same server behind the load balancer. While this is the simplest approach, problems include: the load balancer needs to perform more work, the load distribution could become unbalanced over time, and it is difficult to scale down the infrastructure when the load demand drops since each server will own some sessions. Because of these issues, few PaaS providers support this option.

Set up a shared cache for in-memory HTTP sessions. This way, all servers have all HTTP sessions in-memory at all times. However, replicating the in-memory sessions across a cluster is both bandwidth and computationally intensive. It requires work on the application developer’s side to set up the shared cache and replication strategies.

The application could also be configured to persist all HTTP sessions into the external relational database.

Of all PaaS platforms reviewed, Google App Engine handles this problem best. The Google App Engine is architected to abstract away the notion of individual servers. It automatically creates data stores in separate servers, and saves HTTP session into the data store by default. The process is completely transparent to developers. However, the issue with Google App Engine is that raw performance is poor. It is not uncommon for a web request to take 1-3 seconds to complete a round trip to databases.

Heroku for Java also provides automatic session sharing across server instances because each of its server instances is wrapped around a custom Jetty instance. However, Heroku does not provide transparent auto-scaling. You will have to watch the dashboard and add resources to the app as needed.

For the rest of the standard Java offerings, all of them do a good job forcing the developer to create database tables on a separate, dedicated database server as part of their deployment process. For HTTP sessions, Cloud Foundry uses sticky sessions in its load balancer. As we discussed above, while it makes life easy for developers, it also has some serious scalability issues. The rest of the PaaS offerings leave session management to application developers, although it is not always clear from their documentation.

Amazon Beanstalk CloudBees Cloud Foundry Google App Engine Heroku for Java OpenShift Built-in load balancer Yes Yes Yes Yes Yes Yes Custom domain for load balancer Yes Yes No Google Apps Yes Yes Auto-scaling of app server Yes Yes Planned Yes No Yes Auto-scaling of database No No No Yes No No User defined performance criteria Yes Yes Planned No No Yes Web-based monitoring dashboard Yes Yes Planned Yes Yes Yes Clustered HTTP session Manual Manual Manual Auto Auto Manual

Pricing and Business Concerns

The pricing of those PaaS offerings is an important consideration for developers. Most service providers offer free service tiers for developers to try out. For smaller Java web sites, those free tiers are excellent choices.

However, as Google App Engine’s recent price hike controversy indicated, cost for high volume web applications can be quite high with PaaS providers.

Another important factor to consider is the availability of support options. Google App Engine and Amazon Web Services both have poor track records providing support. Developers are left on their own to find out answers on forums. Smaller providers with Java specialty tend to provide better technical support, even on public forums. In my view CloudBees provides the best combination of paid ticket-based support, and Java-specific technical know-how amongst support staff.

Amazon Beanstalk CloudBees Cloud Foundry Google App Engine Heroku for Java OpenShift Free tier Yes Yes N/A Yes Yes Free Cost for low traffic entry level web apps High Free Free Free Free Free Cross cloud provider No No Planned No No Planned Private cloud No Beta (OpenStack or vSphere) Yes No No Planned Support Forum Email and Phone Forum/Web Support Tickets Forum Email and Phone Forum Support quality Poor Good Good Poor Okay Good

What’s Next

In this article, we reviewed 6 well known vendors in the Java PaaS space. There are of course more smaller or lesser known providers. Examples include

Jelastic: It supports a wide array of combinations of application servers and databases, including variations of the MySQL database and NoSQL databases.

The WSO2 StratosLive: It is a PaaS offering built on the WSO2 application server, which is a Java EE compliant application server.

CumuLogic: It provides a Java application PaaS that works with many private and public cloud solutions including CloudStack, OpenStack and Eucalyptus.

We will keep a close eye on these vendors as they could easily grow up to challenge both the market share and mind share of bigger players.

PaaS for Java has come a long way in the past 12 months. The product offerings are still fast evolving. That is great news for Java developers looking for low cost, scalable, and hassle free hosted solutions. For Java EE developers, I believe that CloudBees and Open Shift offer the “best of the breed” services so far, and with OpenShift still in beta, CloudBees is the winner of this comparison in this highly competitive landscape. If you are willing to venture outside of the Java EE comfort zone, Heroku for Java and Cloud Foundry (beta) are worthy contenders to the venerable Google App Engine.

About the Author

Dr. Michael Yuan is an entrepreneur, author, and Java enthusiast. He has published 5 books and over 40 articles on software engineering, and committed code to noted open source projects such as JBoss and Mozilla. His latest startup, Ringful Health, aims to empower patients to better engage hospital teams and improve health care outcomes using mobile and predictive analytics technologies. Ringful Health’s Java servers are deployed on Google App Engine for Java, Amazon EC2, and CloudBees.