This documentation is for WSO2 ESB version 4.5.1. View documentation for the latest release.

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Enterprise service bus (ESB) is a software architecture construct, which lives between the (business) applications and enables communication among them. Ideally, the ESB should be able to replace all direct contact with the applications on the bus, so that all communication takes place via the ESB.

ESB provides its fundamental services via an event-driven and standards-based messaging engine (the bus). Thanks to ESB, integration architects can exploit the value of messaging without writing code. Developers typically implement an ESB using technologies found in a category of middleware infrastructure products, usually based on recognized standards.

ESB is a relatively new concept. The term has only been in common use for the last several years. People often associate ESBs and Service Oriented Architecture (SOAs) but they are somewhat orthogonal concerns. However, like SOA, ESB is essentially a collection of enterprise architecture design patterns that is now implemented directly by many enterprise software products.

The WSO2 ESB is a fast, light-weight and versatile Enterprise Service Bus product released under the Apache License v2.0. Using WSO2 ESB you can filter, transform, route and manipulate SOAP, binary, plain XML, and text messages that pass through your business systems by HTTP, HTTPS, JMS, mail, etc.

What is new in this Release

The WSO2 ESB version 4.5.1 is the successor of version 4.5.0 and based on Carbon 4.0.2. It has several enhancements and defect fixes included in it.

New Features/Enhancements:

  • Performance enhancements due to refactoring the Carbon context. (Inherited from new and enhanced Carbon 4.0.2)
  • Enhanced performance of the WSO2 Deployment Synchronizer with optimized tenant loading time through the use of ghost artifacts.

Bug Fixes:

The bug fixes included in this release are both in the base framework as well as the ESB specific components. For more information on the defect fixes, refer to the following pages in WSO2 Oxygen Tank:

Known Issues

For a list of known issues in the WSO2 ESB 4.0.5, please refer to the following links in WSO2 Oxygen Tank:

Community Resources

WSO2 is willing to provide you guidance for any technical issues or questions regarding the ESB product. You can communicate with the WSO2 ESB development team directly using the relevant mailing lists mentioned here:

WSO2 encourages you to report issues and enhancement requests for WSO2 ESB using the publicJIRA available at You can also track their resolutions and comment on the progress.

Questions regarding the ESB can also be raised through Ensure that you tag the question with appropriate keywords such as WSO2 and ESB so that our team can easily find your questions and provide answers.

For tutorials, articles, Webinars and similar resources, visit the WSO2 Oxygen Tank and search under the Resources menu.

The Application Programing Interface of Apache Synapse is used underneath WSO2 ESB: This API is useful when you write advanced custom mediators.

Support Options

WSO2 also offers a variety of development and production support programs, ranging from Web-based support during normal business hours, to premium 24x7 phone support. WSO2 is committed to ensuring that your enterprise middleware deployment is completely supported from evaluation to production. Our unique approach ensures that support leverages the open development methodology and is provided by the very same engineers who build the products. For additional support information please refer to

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