JMS Proxy Services with Fail-Over Support

Rajika has written a very comprehensive article about setting up WSO2 ESB with JMS in a fail-over scenario.

The concept of fail-over endpoints is integral to WSO2 ESB. The user can define a fail-over endpoint in the ESB which in turns consists of two or more child endpoints. ESB will select one of the child endpoints to be the primary endpoint and will keep forwarding all messages to this primary endpoint. If the ESB detects some error while communicating with the primary endpoint, it will automatically fail-over to one of the available backup endpoints. User can also configure the endpoint error codes upon which to trigger a fail-over, endpoint suspend durations and timeout durations. However this is not what Rajika is talking about in his article. His article is about setting up a JMS proxy service with fail-over support in the ESB .

For an example imagine a situation where you have setup a proxy service to receive messages from a JMS queue. The ESB proxy service polls messages out of the queue and forwards them to a backend application for further processing. Now what if the ESB instance which hosts the above mentioned proxy service happens to fail (say due to a hardware failure). Actually in this case there's both good news and bad news. Good news is that no messages will get lost due to the persistent behavior of JMS messaging. If some messages were in flight within the ESB when the failure occurred those messages might get lost. But even that can be avoided by using something like JTA. The bad news however is that the backend application will not receive further requests to be processed. So as far as your overall system is concerned, your applications and services will stay idle while messages keep piling up on the JMS queue.

Rajika discusses a possible architecture to avoid such system downtime by having a backup proxy service (ideally deployed in a separate ESB instance) which listens on the same JMS queue. The backup proxy will be disabled by default to prevent contention between the two proxy services. His architecture also utilizes a scheduled task deployed on the backup ESB which sends periodic heartbeats to the other ESB node. If the backup ESB detects that the primary ESB instance is not responding, it will activate the backup proxy service which will start polling for JMS messages and resume operations in the system.

This is actually fairly simple to implement in WSO2 ESB and can be even further customized to suit the exact enterprise requirements. All the source code and relevant configurations are provided in the article itself.

Rediscover SOA with WSO2 Carbon and WS-Discovery

WS-Discovery is a standard protocol for discovering services and endpoints in an SOA based environment. Using WS-Discovery, servers can publish service metadata to a centralized repository known as the discovery proxy. Clients and other interested parties can query the discovery proxy to find a required service or an endpoint.

WSO2 Carbon platform has exceptional support for WS-Discovery. Service hosting products like WSO2 Application Server can publish their services to a user defined discovery proxy. WSO2 Governance Registry can be used as this discovery proxy and products like WSO2 ESB can query a discovery proxy to locate backend service endpoints.

I recently wrote an article explaining how WS-Discovery is supported in the Carbon platform. The article starts by explaining the basics of WS-Discovery and then describes how to build a complete practical solution based on the discovery protocol. The sample solution described in the article, an inventory management system for Trader Paul's department store, uses 4 WSO2 products. Almost all the core business logic of the solution resides in WSO2 Application Server and WSO2 Data Services Server. The web application which provides the UI layer of the solution uses WS-Discovery to dynamically discover the business services and data services. WSO2 Governance Registry acts as the discovery proxy where all the service metadata are stored. The solution also uses WSO2 ESB to expose some of the core services to the public through a secured channel. The article describes how to use the discovery support in ESB to create these proxy services. Further it describes an advanced functionality of the ESB (discovery mediation extensions), using which 100% dynamic proxy services can be created. These dynamic proxy services use the WS-Discovery protocol to discover the backend service endpoints at runtime.

This article shows the real power of the Carbon framework and what we can achieve with it when the appropriate components/products are combined into a single distributed solution. I certainly enjoyed a lot putting up all the samples and writing content for this article. I hope you will get a similar feeling reading it. All the code and configurations used for the samples are also provided so you can run the Trader Paul's Inventory Management System on your own and try it out. I'm currently working on porting this sample to the StratosLive environment. So it will be soon available on the cloud as well. If you are just looking to learn about WS-Discovery, or just trying to understand how to build solutions with WSO2 products, this article would be a great starting point.

WSO2 ESB Documentation Revamped

No software application is complete without documentation. According to Ian Sommerville (author of the well known textbook on Software Engineering), software is not just the computer programs, but also all associated documentation and configuration data that is needed to make the programs operate correctly. According to this definition documentation is not only a key component of software, but it is one of the factors which differentiates software from computer programs. But unfortunately many open source projects are getting hammered for their poorly structured and less comprehensive documentation. WSO2 ESB documentation also used to suffer from a number of such strictures which made it look slightly obfuscated and disorganized to the reader. While the samples and other configuration related documentation was fairly well organized, the overall documentation offering had several gaps in terms of content, user friendliness and ability to search.

However I'm pleased to announce that those days are now behind us. WSO2 ESB now has a brand new documentation package with a whole lot of new content, an exquisite look and feel and a ton of new features. You will find that almost all the old content has been rewritten, reformatted and reshaped to make it more comprehensive and easier to follow. In contrast to the old documentation, the new offering contains many diagrams, sample configurations and much easier navigation capabilities between different sections. Samples are no longer a separate section in the documentation but they are baked into the relative explanatory sections in the documentation. This way the reader can seamlessly move between content and relevant samples.

Perhaps the most significant feature in the new documentation package is its ability to search for content. All the content items have been properly labeled and indexed so the reader can find out what he's looking for by doing a search on the documentation site. Try out following search links to see for yourself.

• http://docs.wso2.org/dosearchsite.action?queryString=ancestorIds:1179863+AND+new+in+version+4.0&where=ESB&type=&lastModified=&contributor=&contributorUsername=
• http://docs.wso2.org/dosearchsite.action?searchQuery.queryString=ancestorIds:1179863+AND+eventing&searchQuery.spaceKey=ESB

As of now you will find documentation related to WSO2 ESB 3.0.1 and WSO2 ESB 4.0.0 in the new documentation site. Please note that this is still very much an ongoing effort. We are continuously working on making our documentation even more comprehensive and easier to follow. Feel free to help us out by pointing out mistakes, limitations and better yet providing new content that we can include in our documentation offering.

WSO2: The Mission, Vision and the Future

That was without a doubt a perfect week. I'm of course talking about the WSO2Con 2011 which was held last month at Colombo, Sri Lanka. We are still trying to cope up with the continuous flow of complements, well wishes, congratulations and thank you notes. There's no doubt in my mind that it was the most elegant and most successful technical event Sri Lanka (and perhaps even Asia) has ever witnessed. We had over 20 technical presentations conducted by people from various countries and organizations. We had participants from all corners of the world; USA, UK, Russia, India, China, New Zealand, Mexico...you name it. If you are doing anything related to web services or SOA that was the place to be. (If you missed it this year, start planning for next year right now)

The opening keynote of WSO2Con delivered by Dr. Sanjiva Weerawarana is now available on-line. This speech is about WSO2, WSO2 history and WSO2 vision. It's about what we have achieved, how we operate and what we intend to conquer in the years to come.

Within just a matter of 6 years, WSO2 has managed to develop a comprehensive SOA middleware platform which consists of around 15 products and a very powerful cloud platform. WSO2 products are used by some of the largest organizations in the world to handle billions of business transactions. WSO2 offers the only complete SOA PaaS in the cloud which is capable of hosting web services, web applications, data services, mashups, business processes, gadgets, integration flows and more. And WSO2 has managed to do all this while adhering to true open source principles and open standards.

This speech is about these great achievements, what motivated us to do what we do and how we are going to scale the game up in the future.