spring-cloud-functions.md

title
Intro to Spring Cloud Functions

Intro to Spring Cloud Functions

Functional Programming for Serverless Spring

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Overview

• What: Spring Cloud Function (SCF) is a project that promotes the implementation of business logic via functions

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Overview

• What: Spring Cloud Function (SCF) is a project that promotes the implementation of business logic via functions
• Why: To 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

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Overview

• What: Spring Cloud Function (SCF) is a project that promotes the implementation of business logic via functions
• Why: To 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
• How: By providing a uniform programming model across serverless providers, as well as the ability to run standalone (locally or in a PaaS)

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Implementation

SCF builds on the 3 core functional interfaces available since Java 8:

• Supplier<O>
• Function<I,O>
• Consumer<I>

Collectively, these are referred to within SCF as "functional beans"

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Applications

SCF instruments Java functions with additional features to be utilised in variety of execution contexts:

• REST support: allows functions to be exposed as HTTP endpoints
• Event-driven microservices: functions can be integrated with cloud events e.g. EventBridge
• Streaming message handler: send or receive messages from a broker (such as Kafka) by leveraging integrations with the Spring Cloud Stream project

There may be more but today's session will explore the first two from the list above

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DEMO

@Component
public class UpperCaseFunction implements Function<String, String> {
  @Override
  public String apply(String value) {
    return value.toUpperCase();
  }
}

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

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

http://localhost:8080/swagger-ui/index.html

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SCF Advantages

• In my experience, does very well to facilitate integrations allowing the developer to focus on business logic
• Enables Spring Boot features (autoconfiguration, dependency injection, metrics, etc.) on serverless providers
• SCF can be public cloud vendor agnostic
  • adapters for MAG (plus others) serverless service providers exist already
• Supports function composition

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Closing Remarks

• Demo Repo contains:
  • SCF x2 following @Bean style
    • GET /healthcheck lambda
    • POST /findAddresses lambda
  • SCF x1 following @Component style
    • EventBridge-triggered lambda
  • Small CDK demo stack to demonstrate necessary lambda configuration
  • Some example SCF unit tests

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Closing Remarks

• Unsure if the best SCF features/practices have been applied
• Open to feedback in the form of code review, PR, written etc.

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