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Mark Fisher
2015-07-16 13:36:35 -04:00
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image::https://travis-ci.org/spring-cloud/spring-cloud-stream.svg?branch=master[Build Status, link=https://travis-ci.org/spring-cloud/spring-cloud-stream]
This project allows a user to develop and run messaging microservices using Spring Integration and run them locally, or in the cloud, or even on Spring XD. Just create `MessageChannels` "input" and/or "output" and add `@EnableChannelBinding` and run your app as a Spring Boot app (single application context). You just need to connect to the physical broker for the bus, which is automatic if the relevant bus implementation is available on the classpath. The sample uses Redis.
This project allows a user to develop and run messaging microservices using Spring Integration and run them locally, or in the cloud, or even on Spring XD. Just create `MessageChannels` "input" and/or "output" and add `@EnableModule` and run your app as a Spring Boot app (single application context). You just need to connect to the physical broker for the bus, which is automatic if the relevant bus implementation is available on the classpath. The sample uses Redis.
Here's a sample source module (output channel only):
[source,java]
----
@SpringBootApplication
@EnableChannelBinding
@EnableModule
@ComponentScan(basePackageClasses=ModuleDefinition.class)
public class ModuleApplication {
@@ -50,8 +50,6 @@ spring:
outputChannelName: ${spring.application.name:ticker}
----
To be deployable as an XD module in a "traditional" way you need `/config/*.properties` to point to any available Java config classes (via `base_packages` or `options_class`), or else you can put traditional XML configuration in `/config/*.xml`. You don't need those things to run as a consumer or producer to an existing XD system, but you do need to replace the `outputChannelName` with `group`, `module` and `index` (the index is a sequential counter that XD uses to label the modules in a stream from left to right). There's an XML version of the same sample (a "timer" source).
== Multiple Input or Output Channels
A module can have multiple input or output channels. Instead of just one channel named "input" or "output" you can add multiple `MessageChannel` beans named `input.*` or `output.*` and the names are converted to external channel names on the broker. The external channel names are the `spring.cloud.streams.[input|output]ChannelName` plus the `MessageChannel` bean name, period separated. In addition, the bean name can be `input.[queue|topic|tap]:*` or `output.[queue|topic]:*` (i.e. with a channel type as a colon-separated prefix), and the semantics of the external bus channel changes accordingly (a tap is like a topic). For example, you can have two `MessageChannels` called "output" and "output.topic:foo" in a module with `outputChannelName=bar`, and the result is 2 external channels called "bar" and "topic:foo.bar".
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There are several samples, all running on the redis transport (so you need redis running locally to test them).
=== Vanilla Module Samples
NOTE: The main set of samples are "vanilla" in the sense that they are not deployable as XD modules by the current generation (1.x) of XD. You can still interact with an XD system using the appropriate naming convention for input and output channel names (`<stream>.<index>` format).
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* `extended` is a multi-module mashup of `source | transform | transform | sink`, where the modules are defined in the other samples and referred to in this app just as dependencies.
=== XD Module Samples
There are several samples, all running on the redis transport (so you need redis running locally to test them):
* `source` is a Java config version of the classic "timer" module from Spring XD. It has a "fixedDelay" option (in milliseconds) for the period between emitting messages.
* `sink` is a Java config version of the classic "log" module from Spring XD. It has no options (but some could easily be added), and just logs incoming messages at INFO level.
* `tap` is the same as the sink sample, except it is configured to tap the source sample output. When it is running it looks a lot like the sink, except that it only gets copies of the messages in the broker, and since it is a pub-sub subscriber, it only gets the messages sent since it started.
* `source-xml` is a copy of the classic "timer" module from Spring XD.
If you run the source and the sink and point them at the same redis instance (e.g. do nothing to get the one on localhost, or the one they are both bound to as a service on Cloud Foundry) then they will form a "stream" and start talking to each other. All the samples have friendly JMX and Actuator endpoints for inspecting what is going on in the system.
== Module or App
Code using this library can be deployed as a standalone app or as an XD module. In standalone mode you app will run happily as a service or in any PaaS (Cloud Foundry, Lattice, Heroku, Azure, etc.). Depending on whether your main aim is to develop an XD module and you just want to test it locally using the standalone mode, or if the ultimate goal is a standalone app, there are some things that you might do differently.
=== Module Options
Module option (placeholders) default values can be set in `/config/*.properties` as per a normal XD module, and they can be overridden at runtime in standalone mode using standard Spring Boot configuration (e.g. `application.yml`). Because of the way XD likes to organize options, the default values can also be set as `option.*` in `bootstrap.yml` (in standalone mode) or as System properties (generally).
=== Local Configuration
The `application.yml` and `bootstrap.yml` files are ignored by XD when deploying the module natively, so you can put whatever you like in there to control the app in standlone mode.
=== Fat JAR
You can run in standalone mode from your IDE for testing. To run in production you can create an executable (or "fat") JAR using the standard Spring Boot tooling, but the executable JAR has a load of stuff in it that isn't needed if it's going to be deployed as an XD module. In that case you are better off with the normal JAR packaging provided by Maven or Gradle.
You can run in standalone mode from your IDE for testing. To run in production you can create an executable (or "fat") JAR using the standard Spring Boot tooling.
// To be confirmed...
// the executable JAR has a load of stuff in it that isn't needed if it's going to be deployed as an XD module. In that case you are better off with the normal JAR packaging provided by Maven or Gradle.
== Making Standalone Modules Talk to Each Other