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<title>11. Inter-Application Communication</title><link rel="stylesheet" type="text/css" href="css/manual-multipage.css"><meta name="generator" content="DocBook XSL Stylesheets V1.79.1"><link rel="home" href="multi_spring-cloud-stream.html" title="Spring Cloud Stream Reference Guide"><link rel="up" href="multi__reference_guide.html" title="Part II. Reference Guide"><link rel="prev" href="multi_schema-evolution.html" title="10. Schema Evolution Support"><link rel="next" href="multi__testing.html" title="12. Testing"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">11. Inter-Application Communication</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="multi_schema-evolution.html">Prev</a> </td><th width="60%" align="center">Part II. Reference Guide</th><td width="20%" align="right"> <a accesskey="n" href="multi__testing.html">Next</a></td></tr></table><hr></div><div class="chapter"><div class="titlepage"><div><div><h2 class="title"><a name="_inter_application_communication" href="#_inter_application_communication"></a>11. Inter-Application Communication</h2></div></div></div><p>Spring Cloud Stream enables communication between applications. Inter-application communication is a complex issue spanning several concerns, as described in the following topics:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><span class="quote">“<span class="quote"><a class="xref" href="multi__inter_application_communication.html#spring-cloud-stream-overview-connecting-multiple-application-instances" title="11.1 Connecting Multiple Application Instances">Section 11.1, “Connecting Multiple Application Instances”</a></span>”</span></li><li class="listitem"><span class="quote">“<span class="quote"><a class="xref" href="multi__inter_application_communication.html#spring-cloud-stream-overview-instance-index-instance-count" title="11.2 Instance Index and Instance Count">Section 11.2, “Instance Index and Instance Count”</a></span>”</span></li><li class="listitem"><span class="quote">“<span class="quote"><a class="xref" href="multi__inter_application_communication.html#spring-cloud-stream-overview-partitioning" title="11.3 Partitioning">Section 11.3, “Partitioning”</a></span>”</span></li></ul></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="spring-cloud-stream-overview-connecting-multiple-application-instances" href="#spring-cloud-stream-overview-connecting-multiple-application-instances"></a>11.1 Connecting Multiple Application Instances</h2></div></div></div><p>While Spring Cloud Stream makes it easy for individual Spring Boot applications to connect to messaging systems, the typical scenario for Spring Cloud Stream is the creation of multi-application pipelines, where microservice applications send data to each other.
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<title>11. Inter-Application Communication</title><link rel="stylesheet" type="text/css" href="css/manual-multipage.css"><meta name="generator" content="DocBook XSL Stylesheets V1.79.1"><link rel="home" href="multi_spring-cloud-stream.html" title="Spring Cloud Stream Reference Guide"><link rel="up" href="multi__preface.html" title="Part I. Preface"><link rel="prev" href="multi_schema-evolution.html" title="10. Schema Evolution Support"><link rel="next" href="multi__testing.html" title="12. Testing"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">11. Inter-Application Communication</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="multi_schema-evolution.html">Prev</a> </td><th width="60%" align="center">Part I. Preface</th><td width="20%" align="right"> <a accesskey="n" href="multi__testing.html">Next</a></td></tr></table><hr></div><div class="chapter"><div class="titlepage"><div><div><h2 class="title"><a name="_inter_application_communication" href="#_inter_application_communication"></a>11. Inter-Application Communication</h2></div></div></div><p>Spring Cloud Stream enables communication between applications. Inter-application communication is a complex issue spanning several concerns, as described in the following topics:</p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><span class="quote">“<span class="quote"><a class="xref" href="multi__inter_application_communication.html#spring-cloud-stream-overview-connecting-multiple-application-instances" title="11.1 Connecting Multiple Application Instances">Section 11.1, “Connecting Multiple Application Instances”</a></span>”</span></li><li class="listitem"><span class="quote">“<span class="quote"><a class="xref" href="multi__inter_application_communication.html#spring-cloud-stream-overview-instance-index-instance-count" title="11.2 Instance Index and Instance Count">Section 11.2, “Instance Index and Instance Count”</a></span>”</span></li><li class="listitem"><span class="quote">“<span class="quote"><a class="xref" href="multi__inter_application_communication.html#spring-cloud-stream-overview-partitioning" title="11.3 Partitioning">Section 11.3, “Partitioning”</a></span>”</span></li></ul></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="spring-cloud-stream-overview-connecting-multiple-application-instances" href="#spring-cloud-stream-overview-connecting-multiple-application-instances"></a>11.1 Connecting Multiple Application Instances</h2></div></div></div><p>While Spring Cloud Stream makes it easy for individual Spring Boot applications to connect to messaging systems, the typical scenario for Spring Cloud Stream is the creation of multi-application pipelines, where microservice applications send data to each other.
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You can achieve this scenario by correlating the input and output destinations of <span class="quote">“<span class="quote">adjacent</span>”</span> applications.</p><p>Suppose a design calls for the Time Source application to send data to the Log Sink application. You could use a common destination named <code class="literal">ticktock</code> for bindings within both applications.</p><p>Time Source (that has the channel name <code class="literal">output</code>) would set the following property:</p><pre class="screen">spring.cloud.stream.bindings.output.destination=ticktock</pre><p>Log Sink (that has the channel name <code class="literal">input</code>) would set the following property:</p><pre class="screen">spring.cloud.stream.bindings.input.destination=ticktock</pre></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="spring-cloud-stream-overview-instance-index-instance-count" href="#spring-cloud-stream-overview-instance-index-instance-count"></a>11.2 Instance Index and Instance Count</h2></div></div></div><p>When scaling up Spring Cloud Stream applications, each instance can receive information about how many other instances of the same application exist and what its own instance index is.
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Spring Cloud Stream does this through the <code class="literal">spring.cloud.stream.instanceCount</code> and <code class="literal">spring.cloud.stream.instanceIndex</code> properties.
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For example, if there are three instances of a HDFS sink application, all three instances have <code class="literal">spring.cloud.stream.instanceCount</code> set to <code class="literal">3</code>, and the individual applications have <code class="literal">spring.cloud.stream.instanceIndex</code> set to <code class="literal">0</code>, <code class="literal">1</code>, and <code class="literal">2</code>, respectively.</p><p>When Spring Cloud Stream applications are deployed through Spring Cloud Data Flow, these properties are configured automatically; when Spring Cloud Stream applications are launched independently, these properties must be set correctly.
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@@ -34,4 +34,4 @@ With Kafka, if <code class="literal">autoRebalanceEnabled</code> is <code class=
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If <code class="literal">autoRebalanceEnabled</code> is set to false, the <code class="literal">instanceCount</code> and <code class="literal">instanceIndex</code> are used by the binder to determine which partition(s) the instance subscribes to (you must have at least as many partitions as there are instances).
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The binder allocates the partitions instead of Kafka.
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This might be useful if you want messages for a particular partition to always go to the same instance.
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When a binder configuration requires them, it is important to set both values correctly in order to ensure that all of the data is consumed and that the application instances receive mutually exclusive datasets.</p><p>While a scenario in which using multiple instances for partitioned data processing may be complex to set up in a standalone case, Spring Cloud Dataflow can simplify the process significantly by populating both the input and output values correctly and by letting you rely on the runtime infrastructure to provide information about the instance index and instance count.</p></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="multi_schema-evolution.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="multi__reference_guide.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="multi__testing.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">10. Schema Evolution Support </td><td width="20%" align="center"><a accesskey="h" href="multi_spring-cloud-stream.html">Home</a></td><td width="40%" align="right" valign="top"> 12. Testing</td></tr></table></div></body></html>
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When a binder configuration requires them, it is important to set both values correctly in order to ensure that all of the data is consumed and that the application instances receive mutually exclusive datasets.</p><p>While a scenario in which using multiple instances for partitioned data processing may be complex to set up in a standalone case, Spring Cloud Dataflow can simplify the process significantly by populating both the input and output values correctly and by letting you rely on the runtime infrastructure to provide information about the instance index and instance count.</p></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="multi_schema-evolution.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="multi__preface.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="multi__testing.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">10. Schema Evolution Support </td><td width="20%" align="center"><a accesskey="h" href="multi_spring-cloud-stream.html">Home</a></td><td width="40%" align="right" valign="top"> 12. Testing</td></tr></table></div></body></html>
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