How to Use a Load Balance Endpoint¶
Session Affinity Load Balancing between Three Endpoints
This sample demonstrates how the Micro Integrator can handle load balancing with
session affinity using simple client sessions. Here the
session type is specified as simpleClientSession
.
This is a client initiated session, which means that the client
generates the session identifier and sends it with each request. In this
sample session type, the client adds a SOAP header named ClientID
containing the identifier of the client. The MI binds this ID with a
server on the first request and sends all successive requests containing
that ID to the same server.
Synapse configuration¶
Following is a sample REST API configuration that we can used to implement this scenario.
<proxy name="LoadBalanceProxy" startOnLoad="true" transports="http https" xmlns="http://ws.apache.org/ns/synapse">
<target>
<inSequence>
<header name="Action" value="urn:placeOrder"/>
<call>
<endpoint>
<!-- specify the session as the simple client session provided by Synapse for
testing purpose -->
<session type="simpleClientSession"/>
<loadbalance>
<endpoint>
<address uri="http://localhost:9001/services/SimpleStockQuoteService">
<enableAddressing/>
</address>
</endpoint>
<endpoint>
<address uri="http://localhost:9002/services/SimpleStockQuoteService">
<enableAddressing/>
</address>
</endpoint>
<endpoint>
<address uri="http://localhost:9003/services/SimpleStockQuoteService">
<enableAddressing/>
</address>
</endpoint>
</loadbalance>
</endpoint>
</call>
<respond/>
</inSequence>
<faultSequence>
<sequence key="errorHandler"/>
</faultSequence>
</target>
</proxy>
<sequence name="errorHandler" xmlns="http://ws.apache.org/ns/synapse">
<makefault version="soap11">
<code value="soap11Env:VersionMismatch" xmlns:soap11Env="http://schemas.xmlsoap.org/soap/envelope/"/>
<reason value="COULDN'T SEND THE MESSAGE TO THE SERVER."/>
</makefault>
<header name="To" action="remove"/>
<property name="RESPONSE" value="true"/>
<send/>
</sequence>
Build and run¶
Create the artifacts:
-
Launch Visual Studio Code with the Micro Integrator for VS Code extension (MI for VS Code) installed.
Info
Follow the Install Micro Integrator for VS Code documentation for a complete installation guide.
-
Create an integration project.
- Create the Proxy and the Sequence with the configurations given above.
- Deploy the artifacts in your Micro Integrator.
Set up the back-end service:
- Download the back-end service.
- Extract the downloaded zip file.
- Open a terminal, navigate to the
axis2Server/bin/
directory inside the extracted folder. -
Execute the following command to start the axis2server with the SimpleStockQuote back-end service:
sh axis2server.sh
axis2server.bat
-
Open the
tcpmon
application, which is in theMI_HOME/bin/
directory. - Configure
tcpmon
to listen to ports9001, 9002, and 9003
and set the target hostname tolocalhost
and target port to9000
in each instance.
Invoking the proxy service:
Send the following request 3 or more times. Make sure to include a simpleClientSession
to the header.
POST http://localhost:8290/services/LoadBalanceProxy HTTP/1.1
Content-Type: text/xml;charset=UTF-8
simpleClientSession: 123
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
<soapenv:Header/>
<soapenv:Body>
<m0:placeOrder xmlns:m0="http://services.samples">
<m0:order>
<m0:price>172.23182849731984</m0:price>
<m0:quantity>18398</m0:quantity>
<m0:symbol>IBM</m0:symbol>
</m0:order>
</m0:placeOrder>
</soapenv:Body>
</soapenv:Envelope>
Analyzing the output:
When inspecting the tcpmon
, you will see that each listener
has received a request (If you have only sent 3 requests, otherwise more than 1). This is because,
when multiple requests are sent with the same session ID, they are distributed across
the three endpoints in a round robin manner.