372 lines
24 KiB
XML
372 lines
24 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<?asciidoc-toc?>
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<?asciidoc-numbered?>
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<book xmlns="http://docbook.org/ns/docbook" xmlns:xl="http://www.w3.org/1999/xlink" version="5.0" xml:lang="en">
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<info>
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<title>Spring Cloud Function</title>
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<date>2018-06-02</date>
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</info>
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<preface>
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<title></title>
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<simpara>Mark Fisher, Dave Syer</simpara>
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<simpara><?asciidoc-hr?></simpara>
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</preface>
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<chapter xml:id="_introduction">
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<title>Introduction</title>
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<simpara>Spring Cloud Function is a project with the following high-level goals:</simpara>
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<itemizedlist>
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<listitem>
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<simpara><emphasis>Promote the implementation of business logic via functions.</emphasis></simpara>
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</listitem>
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<listitem>
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<simpara><emphasis>Decouple the development lifecycle of business logic from any specific runtime target so that the same code can run as a web endpoint, a stream processor, or a task.</emphasis></simpara>
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</listitem>
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<listitem>
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<simpara><emphasis>Support a uniform programming model across serverless providers, as well as the ability to run standalone (locally or in a PaaS).</emphasis></simpara>
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</listitem>
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<listitem>
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<simpara><emphasis>Enable Spring Boot features (auto-configuration, dependency injection, metrics) on serverless providers.</emphasis></simpara>
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</listitem>
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</itemizedlist>
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<simpara>It abstracts away all of the transport details and
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infrastructure, allowing the developer to keep all the familiar tools
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and processes, and focus firmly on business logic.</simpara>
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<simpara>Here’s a complete, executable, testable Spring Boot application
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(implementing a simple string manipulation):</simpara>
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<programlisting language="java" linenumbering="unnumbered">@SpringBootApplication
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public class Application {
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@Bean
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public Function<Flux<String>, Flux<String>> uppercase() {
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return flux -> flux.map(value -> value.toUpperCase());
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}
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public static void main(String[] args) {
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SpringApplication.run(Application.class, args);
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}
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}</programlisting>
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<simpara>It’s just a Spring Boot application, so it can be built, run and
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tested, locally and in a CI build, the same way as any other Spring
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Boot application. The <literal>Function</literal> is from <literal>java.util</literal> and <literal>Flux</literal> is a
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<link xl:href="http://www.reactive-streams.org/">Reactive Streams</link> <literal>Publisher</literal> from
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<link xl:href="https://projectreactor.io/">Project Reactor</link>. The function can be
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accessed over HTTP or messaging.</simpara>
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<simpara>Spring Cloud Function has 4 main features:</simpara>
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<orderedlist numeration="arabic">
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<listitem>
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<simpara>Wrappers for <literal>@Beans</literal> of type <literal>Function</literal>, <literal>Consumer</literal> and
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<literal>Supplier</literal>, exposing them to the outside world as either HTTP
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endpoints and/or message stream listeners/publishers with RabbitMQ, Kafka etc.</simpara>
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</listitem>
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<listitem>
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<simpara>Compiling strings which are Java function bodies into bytecode, and
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then turning them into <literal>@Beans</literal> that can be wrapped as above.</simpara>
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</listitem>
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<listitem>
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<simpara>Deploying a JAR file containing such an application context with an
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isolated classloader, so that you can pack them together in a single
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JVM.</simpara>
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</listitem>
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<listitem>
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<simpara>Adapters for <link xl:href="https://github.com/spring-cloud/spring-cloud-function/tree/master/spring-cloud-function-adapters/spring-cloud-function-adapter-aws">AWS Lambda</link>, <link xl:href="https://github.com/spring-cloud/spring-cloud-function/tree/master/spring-cloud-function-adapters/spring-cloud-function-adapter-azure">Azure</link>, <link xl:href="https://github.com/spring-cloud/spring-cloud-function/tree/master/spring-cloud-function-adapters/spring-cloud-function-adapter-openwhisk">Apache OpenWhisk</link> and possibly other "serverless" service providers.</simpara>
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</listitem>
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</orderedlist>
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<note>
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<simpara>Spring Cloud is released under the non-restrictive Apache 2.0 license. If you would like to contribute to this section of the documentation or if you find an error, please find the source code and issue trackers in the project at <link xl:href="https://github.com/spring-cloud/spring-cloud-function/tree/master/docs/src/main/asciidoc">github</link>.</simpara>
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</note>
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</chapter>
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<chapter xml:id="_getting_started">
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<title>Getting Started</title>
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<simpara>Build from the command line (and "install" the samples):</simpara>
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<screen>$ ./mvnw clean install</screen>
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<simpara>(If you like to YOLO add <literal>-DskipTests</literal>.)</simpara>
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<simpara>Run one of the samples, e.g.</simpara>
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<screen>$ java -jar spring-cloud-function-samples/function-sample/target/*.jar</screen>
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<simpara>This runs the app and exposes its functions over HTTP, so you can
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convert a string to uppercase, like this:</simpara>
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<screen>$ curl -H "Content-Type: text/plain" localhost:8080/uppercase -d Hello
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HELLO</screen>
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<simpara>You can convert multiple strings (a <literal>Flux<String></literal>) by separating them
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with new lines</simpara>
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<screen>$ curl -H "Content-Type: text/plain" localhost:8080/uppercase -d 'Hello
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> World'
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HELLOWORLD</screen>
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<simpara>(You can use <literal><superscript>Q</superscript>J</literal> in a terminal to insert a new line in a literal
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string like that.)</simpara>
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</chapter>
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<chapter xml:id="_building_and_running_a_function">
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<title>Building and Running a Function</title>
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<simpara>The sample <literal>@SpringBootApplication</literal> above has a function that can be
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decorated at runtime by Spring Cloud Function to be an HTTP endpoint,
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or a Stream processor, for instance with RabbitMQ, Apache Kafka or
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JMS.</simpara>
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<simpara>The <literal>@Beans</literal> can be <literal>Function</literal>, <literal>Consumer</literal> or <literal>Supplier</literal> (all from
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<literal>java.util</literal>), and their parametric types can be String or POJO. A
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<literal>Function</literal> is exposed as a Spring Cloud Stream <literal>Processor</literal> if
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<literal>spring-cloud-function-stream</literal> is on the classpath.
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A <literal>Consumer</literal> is also exposed as a Stream
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<literal>Sink</literal> and a <literal>Supplier</literal> translates to a Stream <literal>Source</literal>.
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HTTP endpoints are exposed if the Stream binder is <literal>spring-cloud-stream-binder-servlet</literal>.</simpara>
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<simpara>Functions can be of <literal>Flux<String></literal> or <literal>Flux<Pojo></literal> and Spring Cloud
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Function takes care of converting the data to and from the desired
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types, as long as it comes in as plain text or (in the case of the
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POJO) JSON. TBD: support for <literal>Flux<Message<Pojo>></literal> and maybe plain
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<literal>Pojo</literal> types (Fluxes implied and implemented by the framework).</simpara>
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<simpara>Functions can be grouped together in a single application, or deployed
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one-per-jar. It’s up to the developer to choose. An app with multiple
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functions can be deployed multiple times in different "personalities",
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exposing different functions over different physical transports.</simpara>
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</chapter>
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<chapter xml:id="_dynamic_compilation">
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<title>Dynamic Compilation</title>
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<simpara>There is a sample app that uses the function compiler to create a
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function from a configuration property. The vanilla "function-sample"
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also has that feature. And there are some examples that you can run to
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see the compilation happening at run time. To run these examples,
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change into the <literal>scripts</literal> directory:</simpara>
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<screen>cd scripts</screen>
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<simpara>Also, start a RabbitMQ server locally (e.g. execute <literal>rabbitmq-server</literal>).</simpara>
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<section xml:id="_start_the_function_registry_service">
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<title>Start the Function Registry Service:</title>
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<screen>./function-registry.sh</screen>
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</section>
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<section xml:id="_register_a_function">
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<title>Register a Function:</title>
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<screen>./registerFunction.sh -n uppercase -f "f->f.map(s->s.toString().toUpperCase())"</screen>
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</section>
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<section xml:id="_run_a_rest_microservice_using_that_function">
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<title>Run a REST Microservice using that Function:</title>
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<screen>./web.sh -f uppercase -p 9000
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curl -H "Content-Type: text/plain" -H "Accept: text/plain" localhost:9000/uppercase -d foo</screen>
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</section>
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<section xml:id="_register_a_supplier">
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<title>Register a Supplier:</title>
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<screen>./registerSupplier.sh -n words -f "()->Flux.just(\"foo\",\"bar\")"</screen>
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</section>
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<section xml:id="_run_a_rest_microservice_using_that_supplier">
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<title>Run a REST Microservice using that Supplier:</title>
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<screen>./web.sh -s words -p 9001
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curl -H "Accept: application/json" localhost:9001/words</screen>
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</section>
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<section xml:id="_register_a_consumer">
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<title>Register a Consumer:</title>
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<screen>./registerConsumer.sh -n print -t String -f "System.out::println"</screen>
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</section>
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<section xml:id="_run_a_rest_microservice_using_that_consumer">
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<title>Run a REST Microservice using that Consumer:</title>
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<screen>./web.sh -c print -p 9002
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curl -X POST -H "Content-Type: text/plain" -d foo localhost:9002/print</screen>
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</section>
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<section xml:id="_run_stream_processing_microservices">
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<title>Run Stream Processing Microservices:</title>
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<simpara>First register a streaming words supplier:</simpara>
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<screen>./registerSupplier.sh -n wordstream -f "()->Flux.interval(Duration.ofMillis(1000)).map(i->\"message-\"+i)"</screen>
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<simpara>Then start the source (supplier), processor (function), and sink (consumer) apps
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(in reverse order):</simpara>
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<screen>./stream.sh -p 9103 -i uppercaseWords -c print
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./stream.sh -p 9102 -i words -f uppercase -o uppercaseWords
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./stream.sh -p 9101 -s wordstream -o words</screen>
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<simpara>The output will appear in the console of the sink app (one message per second, converted to uppercase):</simpara>
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<screen>MESSAGE-0
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MESSAGE-1
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MESSAGE-2
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MESSAGE-3
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MESSAGE-4
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MESSAGE-5
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MESSAGE-6
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MESSAGE-7
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MESSAGE-8
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MESSAGE-9
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...</screen>
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</section>
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</chapter>
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<chapter xml:id="_function_catalog_and_flexible_function_signatures">
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<title>Function Catalog and Flexible Function Signatures</title>
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<simpara>One of the main features of Spring Cloud Function is to adapt and
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support a range of type signatures for user-defined functions. So
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users can supply a bean of type <literal>Function<String,String></literal>, for
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instance, and the <literal>FunctionCatalog</literal> will wrap it into a
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<literal>Function<Flux<String>,Flux<String>></literal>. Users don’t normally have to
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care about the <literal>FunctionCatalog</literal> at all, but it is useful to know what
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kind of functions are supported in user code.</simpara>
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<simpara>Generally speaking users can expect that if they write a function for
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a plain old Java type (or primitive wrapper), then the function
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catalog will wrap it to a <literal>Flux</literal> of the same type. If the user writes
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a function using <literal>Message</literal> (from spring-messaging) it will receive and
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transmit headers from any adapter that supports key-value metadata
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(e.g. HTTP headers). Here are the details.</simpara>
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<informaltable frame="all" rowsep="1" colsep="1">
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<tgroup cols="3">
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<colspec colname="col_1" colwidth="33.3333*"/>
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<colspec colname="col_2" colwidth="33.3333*"/>
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<colspec colname="col_3" colwidth="33.3334*"/>
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<thead>
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<row>
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<entry align="left" valign="top">User Function</entry>
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<entry align="left" valign="top">Catalog Registration</entry>
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<entry align="left" valign="top"></entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry align="left" valign="top"><simpara><literal>Function<S,T></literal></simpara></entry>
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<entry align="left" valign="top"><simpara><literal>Function<Flux<S>, Flux<T>></literal></simpara></entry>
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<entry align="left" valign="top"></entry>
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</row>
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<row>
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<entry align="left" valign="top"><simpara><literal>Function<Message<S>,Message<T>></literal></simpara></entry>
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<entry align="left" valign="top"><simpara><literal>Function<Flux<Message<S>>, Flux<Message<T>>></literal></simpara></entry>
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<entry align="left" valign="top"></entry>
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</row>
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<row>
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<entry align="left" valign="top"><simpara><literal>Function<Flux<S>, Flux<T>></literal></simpara></entry>
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<entry align="left" valign="top"><simpara><literal>Function<Flux<S>, Flux<T>></literal> (pass through)</simpara></entry>
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<entry align="left" valign="top"></entry>
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</row>
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<row>
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<entry align="left" valign="top"><simpara><literal>Supplier<T></literal></simpara></entry>
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<entry align="left" valign="top"><simpara><literal>Supplier<Flux<T>></literal></simpara></entry>
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<entry align="left" valign="top"></entry>
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</row>
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<row>
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<entry align="left" valign="top"><simpara><literal>Supplier<Flux<T>></literal></simpara></entry>
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<entry align="left" valign="top"><simpara><literal>Supplier<Flux<T>></literal></simpara></entry>
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<entry align="left" valign="top"></entry>
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</row>
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<row>
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<entry align="left" valign="top"><simpara><literal>Consumer<T></literal></simpara></entry>
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<entry align="left" valign="top"><simpara><literal>Function<Flux<T>, Mono<Void>></literal></simpara></entry>
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<entry align="left" valign="top"></entry>
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</row>
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<row>
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<entry align="left" valign="top"><simpara><literal>Consumer<Message<T>></literal></simpara></entry>
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<entry align="left" valign="top"><simpara><literal>Function<Flux<Message<T>>, Mono<Void>></literal></simpara></entry>
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<entry align="left" valign="top"></entry>
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</row>
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<row>
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<entry align="left" valign="top"><simpara><literal>Consumer<Flux<T>></literal></simpara></entry>
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<entry align="left" valign="top"><simpara><literal>Consumer<Flux<T>></literal></simpara></entry>
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<entry align="left" valign="top"></entry>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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<simpara>Consumer is a little bit special because it has a <literal>void</literal> return type,
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which implies blocking, at least potentially. Most likely you will not
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need to write <literal>Consumer<Flux<?>></literal>, but if you do need to do that,
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remember to subscribe to the input flux. If you declare a <literal>Consumer</literal>
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of a non publisher type (which is normal), it will be converted to a
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function that returns a publisher, so that it can be subscribed to in
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a controlled way.</simpara>
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<simpara>A function catalog can contain a <literal>Supplier</literal> and a <literal>Function</literal> (or
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<literal>Consumer</literal>) with the same name (like a GET and a POST to the same
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resource). It can even contain a <literal>Consumer<Flux<>></literal> with the same name
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as a <literal>Function</literal>, but it cannot contain a <literal>Consumer<T></literal> and a
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<literal>Function<T,S></literal> with the same name when <literal>T</literal> is not a <literal>Publisher</literal>
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because the consumer would be converted to a <literal>Function</literal> and only one
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of them can be registered.</simpara>
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</chapter>
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<chapter xml:id="_standalone_web_applications">
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<title>Standalone Web Applications</title>
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<simpara>The <literal>spring-cloud-function-web</literal> module has autoconfiguration that
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activates when it is included in a Spring Boot web application (with
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MVC support). There is also a <literal>spring-cloud-starter-function-web</literal> to
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collect all the optional dependnecies in case you just want a simple
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getting started experience.</simpara>
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<simpara>With the web configurations activated your app will have an MVC
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endpoint (on "/" by default, but configurable with
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<literal>spring.cloud.function.web.path</literal>) that can be used to access the
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functions in the application context. The supported content types are
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plain text and JSON.</simpara>
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<informaltable frame="all" rowsep="1" colsep="1">
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<tgroup cols="5">
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<colspec colname="col_1" colwidth="20*"/>
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<colspec colname="col_2" colwidth="20*"/>
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<colspec colname="col_3" colwidth="20*"/>
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<colspec colname="col_4" colwidth="20*"/>
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<colspec colname="col_5" colwidth="20*"/>
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<thead>
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<row>
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<entry align="left" valign="top">Method</entry>
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<entry align="left" valign="top">Path</entry>
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<entry align="left" valign="top">Request</entry>
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<entry align="left" valign="top">Response</entry>
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<entry align="left" valign="top">Status</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry align="left" valign="top"><simpara>GET</simpara></entry>
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<entry align="left" valign="top"><simpara>/{supplier}</simpara></entry>
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<entry align="left" valign="top"><simpara>-</simpara></entry>
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<entry align="left" valign="top"><simpara>Items from the named supplier</simpara></entry>
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<entry align="left" valign="top"><simpara>200 OK</simpara></entry>
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</row>
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<row>
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<entry align="left" valign="top"><simpara>POST</simpara></entry>
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<entry align="left" valign="top"><simpara>/{consumer}</simpara></entry>
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<entry align="left" valign="top"><simpara>JSON object or text</simpara></entry>
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<entry align="left" valign="top"><simpara>Mirrors input and pushes request body into consumer</simpara></entry>
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<entry align="left" valign="top"><simpara>202 Accepted</simpara></entry>
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</row>
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<row>
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<entry align="left" valign="top"><simpara>POST</simpara></entry>
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<entry align="left" valign="top"><simpara>/{consumer}</simpara></entry>
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<entry align="left" valign="top"><simpara>JSON array or text with new lines</simpara></entry>
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<entry align="left" valign="top"><simpara>Mirrors input and pushes body into consumer one by one</simpara></entry>
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<entry align="left" valign="top"><simpara>202 Accepted</simpara></entry>
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</row>
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<row>
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<entry align="left" valign="top"><simpara>POST</simpara></entry>
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<entry align="left" valign="top"><simpara>/{function}</simpara></entry>
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<entry align="left" valign="top"><simpara>JSON object or text</simpara></entry>
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<entry align="left" valign="top"><simpara>The result of applying the named function</simpara></entry>
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<entry align="left" valign="top"><simpara>200 OK</simpara></entry>
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</row>
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<row>
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<entry align="left" valign="top"><simpara>POST</simpara></entry>
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<entry align="left" valign="top"><simpara>/{function}</simpara></entry>
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<entry align="left" valign="top"><simpara>JSON array or text with new lines</simpara></entry>
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<entry align="left" valign="top"><simpara>The result of applying the named function</simpara></entry>
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<entry align="left" valign="top"><simpara>200 OK</simpara></entry>
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</row>
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<row>
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<entry align="left" valign="top"><simpara>GET</simpara></entry>
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<entry align="left" valign="top"><simpara>/{function}/{item}</simpara></entry>
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<entry align="left" valign="top"><simpara>-</simpara></entry>
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<entry align="left" valign="top"><simpara>Convert the item into an object and return the result of applying the function</simpara></entry>
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<entry align="left" valign="top"><simpara>200 OK</simpara></entry>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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<simpara>As the table above shows the behaviour of the endpoint depends on the method and also the type of incoming request data. When the incoming data is single valued, and the target function is declared as obviously single valued (i.e. not returning a collection or <literal>Flux</literal>), then the response will also contain a single value. For multi-valued responses the client can ask for a server-sent event stream by sending `Accept: text/event-stream". If there is only one function (consumer etc.) then the name in the path is optional. Composite functions can be addressed using pipes or commas to separate function names (pipes are legal in URL paths, but a bit awkward to type on the command line).</simpara>
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<simpara>Functions and consumers that are declared with input and output in <literal>Message<?></literal> will see the request headers on the input messages, and the output message headers will be converted to HTTP headers.</simpara>
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<simpara>When POSTing text the response format might be different with Spring Boot 2.0 and older versions, depending on the content negotiation (provide content type and accpt headers for the best results).</simpara>
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</chapter>
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|
<chapter xml:id="_standalone_streaming_applications">
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<title>Standalone Streaming Applications</title>
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<simpara>To send or receive messages from a broker (such as RabbitMQ or Kafka) you can use the <literal>spring-cloud-function-stream</literal> adapter. Add the adapter to your classpath along with the appropriate binder from Spring Cloud Stream. The adapter will bind to the message broker as a <literal>Processor</literal> (input and output streams) unless the user explicitly disables one or the other using <literal>spring.cloud.function.stream.{source,sink}.enabled=false</literal>.</simpara>
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<simpara>An incoming message is routed to a function (or consumer). If there is only one, then the choice is obvious. If there are multiple functions that can accept an incoming message, the message is inspected to see if there is a <literal>stream_routekey</literal> header containing the name of a function. Routing headers or function names can be composed using a comma- or pipe-separated name. The header is also added to outgoing messages from a supplier. Messages with no route key can be routed exclusively to a function or consumer by specifying <literal>spring.cloud.function.stream.{processor,sink}.name</literal>. If a single function cannot be identified to process an incoming message there will be an error, unless you set <literal>spring.cloud.function.stream.shared=true</literal>, in which case such messages will be sent to all compatible functions. A single supplier can be chosen for output messages from a supplier (if more than one is available) using the <literal>spring.cloud.function.stream.source.name</literal>.</simpara>
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<note>
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<simpara>some binders will fail on startup if the message broker is not available and the function catalog contains suppliers that immediately produce messages when accessed. You can switch off the automatic publishing from suppliers on startup using the <literal>spring.cloud.function.strean.supplier.enabled=false</literal> flag.</simpara>
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|
</note>
|
|
</chapter>
|
|
<chapter xml:id="_serverless_platform_adapters">
|
|
<title>Serverless Platform Adapters</title>
|
|
<simpara>As well as being able to run as a standalone process, a Spring Cloud
|
|
Function application can be adapted to run one of the existing
|
|
servlerless platforms. In the project there are adapters for
|
|
<link xl:href="https://github.com/spring-cloud/spring-cloud-function/tree/master/spring-cloud-function-adapters/spring-cloud-function-adapter-aws">AWS
|
|
Lambda</link>,
|
|
<link xl:href="https://github.com/spring-cloud/spring-cloud-function/tree/master/spring-cloud-function-adapters/spring-cloud-function-adapter-azure">Azure</link>,
|
|
and
|
|
<link xl:href="https://github.com/spring-cloud/spring-cloud-function/tree/master/spring-cloud-function-adapters/spring-cloud-function-adapter-openwhisk">Apache
|
|
OpenWhisk</link>. The Oracle Fn platform has its own Spring Cloud Function adapter.</simpara>
|
|
</chapter>
|
|
<chapter xml:id="_deploying_a_packaged_function">
|
|
<title>Deploying a Packaged Function</title>
|
|
<simpara>Spring Cloud Function provides a "deployer" library that allows you to launch a jar file (or exploded archive, or set of jar files) with an isolated class loader and expose the functions defined in it. This is quite a powerful tool that would allow you to, for instance, adapt a function to a range of different input-output adapters without changing the target jar file. Serverless platforms often have this kind of feature built in, so you could see it as a building block for a function invoker in such a platform (indeed the <link xl:href="https://projectriff.io">Riff</link> Java function invoker uses this library).</simpara>
|
|
<simpara>The standard entry point of the API is the Spring configuration annotation <literal>@EnableFunctionDeployer</literal>. If that is used in a Spring Boot application the deployer kicks in and looks for some configuration to tell it where to find the function jar. At a minimum the user has to provide a <literal>function.location</literal> which is a URL or resource location for the archive containing the functions. It can optionally use a <literal>maven:</literal> prefix to locate the artifact via a dependency lookup (see <literal>FunctionProperties</literal> for complete details). A Spring Boot application is bootstrapped from the jar file, using the <literal>MANIFEST.MF</literal> to locate a start class, so that a standard Spring Boot fat jar works well, for example. If the target jar can be launched successfully then the result is a function registered in the main application’s <literal>FunctionCatalog</literal>. The registered function can be applied by code in the main application, even though it was created in an isolated class loader (by default).</simpara>
|
|
</chapter>
|
|
</book> |