WSO2 ESB is a fast, lightweight, open source Enterprise Service Bus implementation. It supports
message routing, inter-mediation, transformation, logging, load balancing, fail over routing,
task scheduling, eventing and much more.
What makes WSO2 ESB unique?
WSO2 ESB is fast and able to handle thousands of concurrent connections with constant memory usage.
It comes with a rich set of mediators to support almost any integration scenario out of the box.
It is also easily extensible and highly customizable. The feature rich admin console makes it
so easy to configure, control and monitor the ESB runtime.
WSO2 ESB is distributed completely free and all the distribution packs can be downloaded from the
WSO2 Oxygen Tank. WSO2 ESB can be downloaded as a binary distribution or a source distribution and
if required one can even checkout the complete source code from the
WSO2 SVN repository.
Does WSO2 ESB has performance comparison with other popular ESBs?
Yes, several rounds of performance comparison has been carried out and the results are available
in WSO2 Oxygen Tank
Is their commercial support available for WSO2 ESB?
We are committed to ensuring that your enterprise middleware deployment is completely supported
from evaluation to production. Our unique approach ensures that all support leverages our open
development methodology and is provided by the very same engineers who build the technology. For
more details and to take advantage of this unique opportunity please visit
Can I get involved with the ESB development activities?
Not only you are allowed, but it is encouraged. You can start by subscribing to firstname.lastname@example.org
and email@example.com mailing lists. Feel free to provide ideas, feed back and help us make our
code better. You can also report bugs on our issue tracker and you can even submit patches. Visit
WSO2 Oxygen Tank for more information about our mailig lists.
Core (Questions related to the Carbon core and underlying framework)
What are the technologies used underneath WSO2 ESB?
WSO2 ESB is built on top of WSO2 Carbon, an OSGi based components framework for SOA. It uses
Apache Synapse as the underlying mediation engine.
Java is the primary programming language used to develop WSO2 ESB.
What are the minimum requirements to run WSO2 ESB?
Pentium 800MHz or equivalent processor
256 MB of memory
The extracted binary distribution of WSO2 ESB takes up about 130 MB of disk space
(WSO2 ESB will require more disk space at runtime to keep temporary files,
server logs etc)
Java Runtime Environment 1.5 or above
What makes WSO2 ESB so fast?
The mediation core of WSO2 ESB is designed to be completely asynchronous, non-blocking and
streaming. It comes with a non-blocking HTTP transport adapter based on Apache HTTP Core-NIO which
is capable of handling a large number of concurrent connections. WSO2 ESB also uses Apache AXIOM, a
StAX based XML infoset model, to process XML and SOAP. This enables WSO2 ESB to stream messages
through the mediation engine without having to invoke slow XML processing routines for each and
Does WSO2 ESB support clustering?
Yes, it supports clustered deployment. WSO2 ESB uses the Apache Axis2 clustering framework to
support the following two clustering schemes:
Multicast based clustering
Well known addressing based clustering
In what occasions do I have to deploy a third party library into WSO2 ESB?
When enabling a new transport you will have to deploy the libraries required by the
transport implementation (eg: When enabling JMS you need to deploy the client libraries required
to connect to your JMS broker)
When adding a custom mediator or a task you might have to deploy the dependencies required
by the custom code
How do I deploy a third party library into the ESB?
You can deploy any third party jar into the repository/components/lib directory. You also need to
restart the server for the newly deployed jars to be picked up by the server runtime. WSO2 ESB will
convert any jar files copied into the above location into OSGi bundles. These OSGi bundles are
placed in the repository/components/dropins directory.
Can I extend the management console UI to add custom UIs ?
Yes, you can extend the management console easily by writing a custom UI component.
Can I use an external user store to manage and authenticate WSO2 ESB users?
Yes you can. You can connect WSO2 ESB with any external user store implementation.
The user store could be LDAP based, JDBC based or a custom developed user store. Please
refer user core documentation for more details.
Does WSO2 ESB interop with a .net client/service?
Yes, it does with both. WSO2 ESB can be easily configured to bridge Java services with .NET clients
and .NET services with Java clients.
Does WSO2 ESB support hessian binary web service protocol
Yes, it does
I don't want some of the features that come with WSO2 ESB. Can I get rid of them?
Yes you can. Login to the ESB management console and browse to the Feature Manager. Open the
'Installed Features' tab. From here you can uninstall any unwanted features.
Can I add support for other language for the management console ?
Yes, WSO2 ESB comes with a UI framework which supports i18n (internationalization) which lets you
to use a language of your choice for the management console.
Mediation (Questions related to sequences, endpoints, proxies etc)
What is a proxy service?
A proxy service is a virtual service hosted on the ESB. It can accept requests from service clients,
just like a real Web Service. A proxy service can process requests and forward them to an actual
Web Service (back end service) to be further processed. The responses coming back from the back
end service can be routed back to the original client. Proxy services are mostly used
to expose an existing service over a different transport, format or QoS configuration.
Does WSO2 ESB has support for transactions ?
Yes it does. It has support for distributed transaction, local JMS transactions and distributed JMS
Does WSO2 ESB has support for PEPPOL?
Yes it does. You can use WSO2 ESB in an Access point.
Where do I have to put my custom mediators in WSO2 ESB?
In version 3.0.1 you can place your non-OSGi custom mediators and class mediators in
$ESB_HOME/repository/components/mediators and OSGi bundles
Where does WSO2 ESB load its configuration from?
WSO2 ESB reads its mediation configuration from a set of XML files located at
repository/conf/synapse-config directory. XML files are written in the Synapse configuration
language. Any changes done to the configuration through the UI are saved back to the configuration
files. (Configuration is also written to the registry by default)
Can I get the ESB to load mediation configuration from the registry?
A mediator is the basic message processing unit in the ESB. A mediator can take a message, carry
out some predefined actions on it and output the modified message. WSO2 ESB ships with a range of
mediators capable of carrying out various tasks on input messages.
Log mediator - Logs the input message
Send mediator - Sends the input message to a given endpoint
XSLT mediator - Transforms the input message using a given XSLT
What is a sequence?
A sequence is an ordered list of mediators (a mediator chain). When a sequence is given a message,
it will go through all the mediators in the sequence. A sequence can also handover messages to
What is an Endpoint?
Endpoint is a target or collection of targets that a message can deliver.
Can Endpoint perform error handling?
Yes. Endpoints can do error handling. User can configure the behavior of an endpoints when it
faced to a erroneous situation. You can find detailed article about endpoint error handling
What are local entries?
Local entries can be used to hold various configuration elements required by sequences and proxy
services. Usually they are used to hold WSDLs, XSDs, XSLT files etc. A local entry can contain XML
content as well as plain text content. A local entry can be configured to load content from a
remote file too.
How can a sequence refer to another sequence?
To refer to a sequence named foo use the sequence mediator as follows:
You can also refer to dynamic sequences saved in the registry by specifying the registry key to the
sequence resource as follows:
The above sequence mediator will load the sequence configuration from the resource at
/dev/sequences/foo in the governance registry.
How does dynamic endpoints and sequences work?
Dynamic endpoints and sequences are just XML configuration bits saved in the registry. These
configurations are loaded to the mediation configuration at runtime. Once loaded they will be cached
for a specified duration in the memory. Once the cache is expired it will be loaded again from the
registry. Therefore changes done to dynamic sequences and endpoints at runtime will take effect
once the ESB reloads them after a cache timeout.
To use dynamic sequences and endpoints the mediation registry must be included in the
mediation configuration as follows:
This configuration can be found in a file named registry.xml in the repository/conf/synapse-config
directory by default. Note how the cache duration is set to 15000 ms (15s). This duration can be
reduced or extended as necessary by editing the registry.xml file or through the configuration
source editor in the UI.
How can I change the endpoint dynamically?
If you want to change the endpoint dynamically per each message, you can use a header mediator to
calculate the new 'To' address.
<header name="To" expression="XPath to create the address dynamically"/>
I have heard of dynamic sequences and endpoints. Are there also dynamic proxy services?
WSO2 ESB does not support dynamic proxy services. But a proxy service may use a dynamic
endpoint as the target endpoint and dynamic sequences as the in sequence and the out sequence.
This effectively makes the entire proxy service dynamic.
I want to mediate messages containing binary content through the ESB. What are the features
available in WSO2 ESB to support my requirement?
How can I implement a persistence mechanism within my mediation chain?
You have two options. One option is to use dbreport and dblookup mediators to
persist the message into a database and lookup it later from the database. The other option is
to use JMS transport in which you can use a JMS broker to persist the message.
I have some dynamic sequences which are loaded from the registry. What will happen to my ESB if
the registry goes down or registry becomes unusable for a while?
If the dynamic sequences are loaded to the memory at least once, the ESB will continue to use the
cached version of the sequence, as long as the registry is unreachable. A warning will be logged
every time ESB attempts to load the sequence from the registry and fails. As soon as the registry
comes back on-line, ESB will load the sequence from the registry.
Transports (Transport related questions)
What are the transports supported by the WSO2 ESB?
WSO2 ESB supports AMQP through its JMS transport. The JMS transport can be configured to
connect to an AMQP broker as if it was connecting to a JMS broker. This functionality has been
tested with Apache Qpid and RabbitMQ.
How to change the host name in WSO2 ESB?
You can edit parameter bind-address in http/https transport receiver to change the host name of WSO2
ESB. This hostname will be displayed on service endpoints and generated WSDLs.
I have several JMS connection factories defined under the JMS transport receiver in the axis2.xml.
How can I get a particular proxy service to receive messages from one of those connection factories?
You can specify the preferred connection factory by adding the following parameter to the proxy
Replace 'MyConnectionFactory' with the name of the appropriate connection factory.
If the above parameter is not specified, proxy service will bind to the connection
factory named 'default'.
Does WSO2 ESB support two way JMS scenario (request/response) ?
Yes, you can refer sample 264
which demonstrates exactly the JMS request/response scenario.
What are the JMS brokers that work with WSO2 ESB?
Any JMS broker that provides JNDI support can be integrated with WSO2 ESB. The default
configurations are for Apache ActiveMQ. WSO2 ESB has also been tested with IBM Websphere MQ,
Swift MQ and JBOSS MQ.
What is the NHTTP transport?
This is the default HTTP transport used by WSO2 ESB. NHTTP stands for non-blocking HTTP.
NHTTP transport uses the Java Non-blocking I/O API. This allows the NHTTP transport to scale into
handling hundreds of connections without blocking the threads. The server worker threads used
by the NHTTP transport do not get blocked on I/O until the ESB receives responses for the already
forwarded requests. Therefore WSO2 ESB can accept more concurrent connections and requests than
most HTTP server products.
What is the underlying HTTP library used by the NHTTP transport?
NHTTP transport uses the
Apache Http Core NIO library underneath. This library provides low level
I/O handling and HTTP level detail handling.
How can I tune up the NHTTP transport?
There is a file called nhttp.properties in the webapps/ROOT/WEB-INF/classes directory. User can
change various configuration parameters like number of threads, keep alive connections through
this file. More information can be found in the ESB Administrator Guide.
Where is the general configuration of NHTTP transport?
The NHTTP transport configuration has two parts and they are transportReceiver and transportSender.
Both configuration are located axis2.xml file.
Production (Questions related to production environments)
Where do I keep the WSDLs required by my proxy services?
You can keep them as local entries. But it is recommended to keep them in the registry instead, for
easier and better management.
What is a graceful shut down?
When a graceful shut down is initiated ESB will serve the accepted requests but stops processing
What are the implications of hot deployment/hot update in a production environment?
Hot deployment/hot update may take the system to inconsistent states if the updates are not properly
coordinated. Therefore it is recommended to turn hot deployment and hot update off for
I already have a WSO2 Governance Registry instance that contains my organization's SOA metadata.
Can I get WSO2 ESB to use that registry instance as the metadata store?
WSO2 ESB integrates with WSO2 Governance Registry out of the box. Refer the administrator
guide for the necessary steps involved in remote registry configuration.
I need to setup a cluster of ESB instances. How can I share the same configuration
among all the ESB nodes?
You just need to put the configuration into the registry and point all ESB instances to that
Deployment (Questions related to ESB deployments)
What are the versions of Java supported by the ESB?
It is tested on JDK 1.5 and JDK 1.6. Sun JDK and IBM JDK are supported.
What are the minimum artifacts required to deploy WSO2?
When deploying you can remove, $ESB_HOME/samples and $ESB_HOME/repository/samples from the
How can I disable the management console ?
You can uninstall all the UI components using the feature manager which will disable the
Does WSO2 ESB supports application server deployments?
Yes it has been tested on the following app servers. JBoss, Weblogic, Websphere and Tomcat.
What are the recommended hardware and software configurations for a typical WSO2 ESB deployment?
2 GHz Multicore processor
2 GB of memory
The extracted binary distribution of WSO2 ESB takes up about 130 MB of disk space
(WSO2 ESB will require more disk space at runtime to keep temporary files,
server logs etc)
Java Runtime Environment 1.6
How can I deploy a custom task?
See the documentation to see how to write a custom task. Put your non-OSGi task jar
into $esbhome/repository/components/lib directory. WSO2 ESB will automatically deploy
your custom task.
How do I embed a third party registry with WSO2 ESB?
You need to write a class implementing the org.apache.synapse.registry.Registry interface to
integrate the third party registry to WSO2 ESB.
What is the database management system used in WSO2 ESB?
WSO2 ESB ships with an embedded H2 database. However any database management system can be plugged
into the ESB via JDBC. The relevant database configurations are available in
repository/conf/registry.xml and repository/cong/user-mgt.xml files. WSO2 ESB has been tested
with MySQL, Oracle, MSSQL and PostgreSQL databases.
How can I change the memory allocation for the WSO2 ESB?
The memory allocation setting are in the wso2server.sh. The user can change the memory allocation
settings by changing the following configuration.
-Xms256m -Xmx512m -XX:MaxPermSize=128m
Does ESB supports JMX monitoring?
Yes it support JMX monitoring. Users can use the JConsole for simple monitoring and use
JMX clients for
Does ESB allows custom statistics collection?
Users can write and plug their own statistics collection mechanisms to the ESB. This allows users
to report statistics to their own statistics collection systems.
What is logging framework used in WSO2 ESB?
WSO2 ESB uses Apache Log4/J over Apache Commons Logging as the logging framework.
Logging configuration is loaded from the log4j.properties file in the lib directory.
The UI also allows configuring logging at runtime. The generated server logs can be found in
the repository/logs directory.
I have a sequence which does not behave the way I want it to. How can I find out what's
wrong with it?
Login to the ESB management console and go to the sequence management page. Enable tracing for the
sequence you want to debug. Send a few messages to the sequence and go to the system logs viewer in
the UI (or open the wso2-esb.log file in repository/logs). Go through the generated trace logs and
locate the problem.
My WSO2 ESB instance is receiving messages. But why I don't see any statistics on the
mediation statistics page?
You need to enable statistics on sequences, endpoints, proxy services for the ESB to collect
statistics on them. By default WSO2 ESB does not collect statistics on anything to keep the overhead
at a minimum. Simply enable statistics for the items you are interested in using the UI and
mediation statistics page will start to get updated.
My ESB instance is behaving weird for certain input messages. What are the tools provided
in the ESB to help me debug the issue?
You can use the SOAP tracer in the UI to capture and monitor actual content of the incoming
messages. Enable tracing on the appropriate sequences to trace the flow of messages through
the ESB. ESB also comes with Apache TCPMon which is a simple but extremely useful too for
monitoring message flows.