:branch: master

=== AWS Lambda

The https://aws.amazon.com/[AWS] adapter takes a Spring Cloud Function app and converts it to a form that can run in AWS Lambda.

The details of how to get stared with AWS Lambda is out of scope of this document, so the expectation is that user has some familiarity with
AWS and AWS Lambda and wants to learn what additional value spring provides.

==== Getting Started

One of the goals of Spring Cloud Function framework is to provide necessary infrastructure elements to enable a _simple function application_
to interact in a certain way in a particular environment.
A simple function application (in context or Spring) is an application that contains beans of type Supplier, Function or Consumer.
So, with AWS it means that a simple function bean should somehow be recognised and executed in AWS Lambda environment.

Let’s look at the example:

[source, java]
----
@SpringBootApplication
public class FunctionConfiguration {

	public static void main(String[] args) {
		SpringApplication.run(FunctionConfiguration.class, args);
	}

	@Bean
	public Function<String, String> uppercase() {
		return value -> value.toUpperCase();
	}
}
----

It shows a complete Spring Boot application with a function bean defined in it. What’s interesting is that on the surface this is just
another boot app, but in the context of AWS Adapter it is also a perfectly valid AWS Lambda application. No other code or configuration
is required. All you need to do is package it and deploy it, so let’s look how we can do that.

To make things simpler we’ve provided a sample project ready to be built and deployed and you can access it
https://github.com/spring-cloud/spring-cloud-function/tree/master/spring-cloud-function-samples/function-sample-aws[here].

You simply execute `./mvnw clean package` to generate JAR file. All the necessary maven plugins have already been setup to generate
appropriate AWS deployable JAR file. (You can read more details about JAR layout in <<Notes on JAR Layout>>).

Then you have to upload the JAR file (via AWS dashboard or AWS CLI) to AWS.

When ask about _handler_ you specify `org.springframework.cloud.function.adapter.aws.FunctionInvoker::handleRequest` which is a generic request handler.

image::{github-raw}/docs/src/main/asciidoc/images/AWS-deploy.png[width=800,scaledwidth="75%",align="center"]

That is all. Save and execute the function with some sample data which for this function is expected to be a
String which function will uppercase and return back.

While `org.springframework.cloud.function.adapter.aws.FunctionInvoker` is a general purpose AWS's `RequestHandler` implementation aimed at completely
isolating you from the specifics of AWS Lambda API, for some cases you may want to specify which specific AWS's `RequestHandler` you want
to use. The next section will explain you how you can accomplish just that.


==== AWS Request Handlers

The adapter has a couple of generic request handlers that you can use. The most generic is (and the one we used in the Getting Started section)
is `org.springframework.cloud.function.adapter.aws.FunctionInvoker` which is the implementation of AWS's `RequestStreamHandler`.
User doesn't need to do anything other then specify it as 'handler' on AWS dashboard when deploying function.
It will handle most of the case including Kinesis, streaming etc. .


If your app has more than one `@Bean` of type `Function` etc. then you can choose the one to use by configuring `spring.cloud.function.definition` 
property or environment variable. The functions are extracted from the Spring Cloud `FunctionCatalog`. In the event you don't specify `spring.cloud.function.definition`
the framework will attempt to find a default following the search order where it searches first for `Function` then `Consumer` and finally `Supplier`).


==== AWS Function Routing

One of the core features of Spring Cloud Function is https://docs.spring.io/spring-cloud-function/docs/{project-version}/reference/html/spring-cloud-function.html#_function_routing_and_filtering[routing] 
- an ability to have one special function to delegate to other functions based on the user provided routing instructions.

In AWS Lambda environment this feature provides one additional benefit, as it allows you to bind a single function (Routing Function) 
as AWS Lambda and thus a single HTTP endpoint for API Gateway. So in the end you only manage one function and one endpoint, while benefiting 
from many function that can be part of your application.

More details are available in the provided https://github.com/spring-cloud/spring-cloud-function/tree/main/spring-cloud-function-samples/function-sample-aws-routing[sample],
yet few general things worth mentioning.

Routing capabilities will be enabled by default whenever there is more then one function in your application as `org.springframework.cloud.function.adapter.aws.FunctionInvoker`
can not determine which function to bind as AWS Lambda, so it defaults to `RoutingFunction`.
This means that all you need to do is provide routing instructions which you can do https://docs.spring.io/spring-cloud-function/docs/{project-version}/reference/html/spring-cloud-function.html#_function_routing_and_filtering[using several mechanisms] 
(see https://github.com/spring-cloud/spring-cloud-function/tree/main/spring-cloud-function-samples/function-sample-aws-routing[sample] for more details).

Also, note that since AWS does not allow dots `.` and/or hyphens`-` in the name of the environment variable, you can benefit from boot support and simply substitute
dots with underscores and hyphens with camel case.  So for example `spring.cloud.function.definition` becomes `spring_cloud_function_definition`
and `spring.cloud.function.routing-expression` becomes `spring_cloud_function_routingExpression`. 


==== Notes on JAR Layout

You don't need the Spring Cloud Function Web or Stream adapter at runtime in Lambda, so you might
need to exclude those before you create the JAR you send to AWS. A Lambda application has to be
shaded, but a Spring Boot standalone application does not, so you can run the same app using 2
separate jars (as per the sample). The sample app creates 2 jar files, one with an `aws`
classifier for deploying in Lambda, and one [[thin-jar,thin jar]] executable (thin) jar that includes `spring-cloud-function-web`
at runtime. Spring Cloud Function will try and locate a "main class" for you from the JAR file
manifest, using the `Start-Class` attribute (which will be added for you by the Spring Boot
tooling if you use the starter parent). If there is no `Start-Class` in your manifest you can
use an environment variable or system property `MAIN_CLASS` when you deploy the function to AWS.

If you are not using the functional bean definitions but relying on Spring Boot's auto-configuration,
then additional transformers must be configured as part of the maven-shade-plugin execution.

[[shade-plugin-setup]]
[source, xml]
----
<plugin>
	<groupId>org.apache.maven.plugins</groupId>
	<artifactId>maven-shade-plugin</artifactId>
	<dependencies>
		<dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-maven-plugin</artifactId>
		</dependency>
	</dependencies>
	<configuration>
		<createDependencyReducedPom>false</createDependencyReducedPom>
		<shadedArtifactAttached>true</shadedArtifactAttached>
		<shadedClassifierName>aws</shadedClassifierName>
		<transformers>
			<transformer implementation="org.apache.maven.plugins.shade.resource.AppendingTransformer">
				<resource>META-INF/spring.handlers</resource>
			</transformer>
			<transformer implementation="org.springframework.boot.maven.PropertiesMergingResourceTransformer">
				<resource>META-INF/spring.factories</resource>
			</transformer>
			<transformer implementation="org.apache.maven.plugins.shade.resource.AppendingTransformer">
				<resource>META-INF/spring.schemas</resource>
			</transformer>
		</transformers>
	</configuration>
</plugin>
----

==== Build file setup

In order to run Spring Cloud Function applications on AWS Lambda, you can leverage Maven or Gradle
 plugins offered by the cloud platform provider.


===== Maven

In order to use the adapter plugin for Maven, add the plugin dependency to your `pom.xml`
file:

[source,xml]
----
<dependencies>
	<dependency>
		<groupId>org.springframework.cloud</groupId>
		<artifactId>spring-cloud-function-adapter-aws</artifactId>
	</dependency>
</dependencies>
----

As pointed out in the <<Notes on JAR Layout>>, you will need a shaded jar in order to upload it
to AWS Lambda. You can use the https://maven.apache.org/plugins/maven-shade-plugin/[Maven Shade Plugin] for that.
The example of the <<shade-plugin-setup,setup>> can be found above.

You can use theSpring Boot Maven Plugin to generate the <<thin-jar>>.
[source,xml]
----
<plugin>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-maven-plugin</artifactId>
	<dependencies>
		<dependency>
			<groupId>org.springframework.boot.experimental</groupId>
			<artifactId>spring-boot-thin-layout</artifactId>
			<version>${wrapper.version}</version>
		</dependency>
	</dependencies>
</plugin>
----

You can find the entire sample `pom.xml` file for deploying Spring Cloud Function
applications to AWS Lambda with Maven https://github.com/spring-cloud/spring-cloud-function/blob/{branch}/spring-cloud-function-samples/function-sample-aws/pom.xml[here].

===== Gradle

In order to use the adapter plugin for Gradle, add the dependency to your `build.gradle` file:

[source,groovy]
----

dependencies {
	compile("org.springframework.cloud:spring-cloud-function-adapter-aws:${version}")
}
----

As pointed out in <<Notes on JAR Layout>>, you will need a shaded jar in order to upload it
to AWS Lambda. You can use the https://plugins.gradle.org/plugin/com.github.johnrengelman.shadow/[Gradle Shadow Plugin] for that:

[source,groovy]
----
buildscript {
	dependencies {
		classpath "com.github.jengelman.gradle.plugins:shadow:${shadowPluginVersion}"
	}
}
apply plugin: 'com.github.johnrengelman.shadow'

assemble.dependsOn = [shadowJar]

import com.github.jengelman.gradle.plugins.shadow.transformers.*

shadowJar {
	classifier = 'aws'
	dependencies {
		exclude(
			dependency("org.springframework.cloud:spring-cloud-function-web:${springCloudFunctionVersion}"))
	}
	// Required for Spring
	mergeServiceFiles()
	append 'META-INF/spring.handlers'
	append 'META-INF/spring.schemas'
	append 'META-INF/spring.tooling'
	transform(PropertiesFileTransformer) {
		paths = ['META-INF/spring.factories']
		mergeStrategy = "append"
	}
}

----

You can use the Spring Boot Gradle Plugin and Spring Boot Thin Gradle Plugin to generate
the <<thin-jar>>.

[source,groovy]
----
buildscript {
	dependencies {
		classpath("org.springframework.boot.experimental:spring-boot-thin-gradle-plugin:${wrapperVersion}")
		classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
	}
}
apply plugin: 'org.springframework.boot'
apply plugin: 'org.springframework.boot.experimental.thin-launcher'
assemble.dependsOn = [thinJar]
----

You can find the entire sample `build.gradle` file for deploying Spring Cloud Function
applications to AWS Lambda with Gradle https://github.com/spring-cloud/spring-cloud-function/blob/{branch}/spring-cloud-function-samples/function-sample-aws/build.gradle[here].

==== Upload

Build the sample under `spring-cloud-function-samples/function-sample-aws` and upload the `-aws` jar file to Lambda. The handler can be `example.Handler` or `org.springframework.cloud.function.adapter.aws.SpringBootStreamHandler` (FQN of the class, _not_ a method reference, although Lambda does accept method references).

----
./mvnw -U clean package
----

Using the AWS command line tools it looks like this:

----
aws lambda create-function --function-name Uppercase --role arn:aws:iam::[USERID]:role/service-role/[ROLE] --zip-file fileb://function-sample-aws/target/function-sample-aws-2.0.0.BUILD-SNAPSHOT-aws.jar --handler org.springframework.cloud.function.adapter.aws.SpringBootStreamHandler --description "Spring Cloud Function Adapter Example" --runtime java8 --region us-east-1 --timeout 30 --memory-size 1024 --publish
----

The input type for the function in the AWS sample is a Foo with a single property called "value". So you would need this to test it:

----
{
  "value": "test"
}
----

NOTE: The AWS sample app is written in the "functional" style (as an `ApplicationContextInitializer`). This is much faster on startup in Lambda than the traditional `@Bean` style, so if you don't need `@Beans` (or `@EnableAutoConfiguration`) it's a good choice. Warm starts are not affected.


==== Type Conversion

Spring Cloud Function will attempt to transparently handle type conversion between the raw
input stream and types declared by your function.

For example, if your function signature is as such `Function<Foo, Bar>` we will attempt to convert
incoming stream event to an instance of `Foo`.

In the event type is not known or can not be determined (e.g., `Function<?, ?>`) we will attempt to
convert an incoming stream event to a generic `Map`.

====== Raw Input

There are times when you may want to have access to a raw input. In this case all you need is to declare your
function signature to accept `InputStream`. For example, `Function<InputStream, ?>`. In this case
we will not attempt any conversion and will pass the raw input directly to a function.





