Introducing Serverlesspresso Extensions

Today the Serverless DA team is launching Serverlesspresso Extensions, a new program that lets you contribute to Serverlesspresso. The best extensions will be added to the Serverlesspresso application running in production and featured on the AWS Compute Blog.

What is Serverlesspresso?

Serverlesspresso is a multi-tenant event-driven serverless application for a pop-up coffee bar that allows you to order from your phone. In 2022, Serverlesspresso processed over 20,000 orders at technology events around the world. At this year’s re:Invent, it featured in the keynote of Amazon CTO, Dr Werner Vogels. It was showcased as an example of an event-driven application that can be easily evolved.

The architecture comprises several serverless apps and has been open-source and freely available since it was launched at re:Invent 2021.

What is extensibility?

Extensibility is the ability to add new functionality to an existing piece of software without modifying the core code already in place. Extensions for web browsers are an example of how useful extensibility can be. The core web browser code is not changed or affected when third parties write extensions, but end users can gain new, rich functionality not envisioned or intended by the original browser authors.

In many production business applications extensibility can help you keep up with the pace of your users requests. It allows you to create new and useful functionality without having to rearchitect the core, original part of your code. Choosing an architectural style that supports this concept can help you retain flexibility as your users needs change.

How EDA supports extensibility

Serverlesspresso is built on an event-driven architecture (EDA). This is an architecture style that uses events to decouple an application’s components. Event-driven architecture offers an effective way to create loosely coupled communication between microservices. This makes it a good architectural choice when you are designing workloads that will require extensibility.

Loosely coupled microservices are able to scale and fail independently, increasing the resilience of the application. Development teams can build and release features for their team’s microservice quickly, without needing to worry about the behavior of other microservices in the application. In addition, new features can be added on top of existing events without making changes to the rest of the application.

Choreography and orchestration are two different models for how distributed services can communicate with one another. In orchestration, communication is more tightly controlled. A central service coordinates the interaction and order in which services are invoked.

Choreography achieves communication without tight control. Events flow between services without any centralized coordination. Many applications, including Serverlesspresso use both choreography and orchestration for different use cases. Event buses such as Amazon EventBridge can be used for choreography, and workflow orchestration services like AWS Step Functions can help build for orchestration.

New functional requirements come up all the time in production applications. We can address new requirements for an event driven application by creating new rules for events in the Event Bus. These rules can add new functionality to the application without having any impact to the existing application stack.

Characteristics of a Serverlesspresso EDA extension

1. Extension resources do not have permission to interact with resources outside the extension definition (including core app resources).
2. Extensions must contain at least one new EventBridge rule that routes existing Serverlesspresso events.
3. Extensions can be deployed and deleted independently of other extensions and the core application.

Building a Serverlesspresso extension

This section shows how to build an extension for Serverlesspresso that adds new functionality while remaining decoupled from the core application. Anyone can contribute an extension to Serverlesspresso. Use the Serverlesspresso extensions GitHub repository to host your extension:

1. Complete the GitHub issue template:
   
2. Clone the repository. Duplicate, and rename the example _extension_model directory.
3. Add the associated extension template and source files.
4. Add the required meta information to `README.md`.
5. Make a pull request to the repository with the new extension files.

Additional guidance can be found in the repository’s PUBLISHING.md file.

Tools and resources to help you build

Event decoupling introduces a new set of challenges. Finding events and their schema can be a difficult process. Developers must coordinate with the team responsible for publishing an event, or look through documentation to find its schema, and then manually create an object for the event in order to use it in their code.

The Amazon EventBridge schema registry helps solve this challenge. It automatically finds events and their structure, or schema, and stores them in a shared central location. For serverlesspresso Extensions, we have created the Serverlesspresso events catalog, and filled it with events from the EventBridge schema registry. Here, all Serverlesspresso events have been documented to help you understand how to use them in your extensions. This includes the services that produce and consumer the event as well as example schemes for each event.

The event player

The event player is a Step Functions workflow that simulates 15 minutes of operation at the Serverlesspresso bar. It does this by replaying an array of realistic events. Use the event player to generate Serverlesspresso events, when building and testing your extensions. Each event is emitted onto an event bus named Serverlesspresso.

1. Clone this repository: git clone https://github.com/aws-samples/serverless-coffee.git
2. Change directory to the event player: cd extensibility/EventPlayer
3. Deploy the EventPlayer using the AWS SAM CLI:
   sam build && sam deploy --guided

This deploys a Step Functions workflow and a custom event bus called “Serverlesspresso”

Running the events player

1. Open the event player from the AWS Management Console.
2. Choose Start execution, leave the default input payload and choose Start execution.

The player takes approximately 15 minutes to complete.

About your extension submission

Extensions will be reviewed by the Serverless DA team within 14 days of submission. When submitting your extension, your extension will become part of the open source offering and is covered by the existing license in the repo. It may be used by any customer under the same license. For additional guidance and ideas to help build your Serverlesspresso extensions, use the following resources:

• Learn more about Serverlesspresso!
• The serverlesspresso workshop
• What is Event driven Architecture
• Building next-gen applications with event-driven architectures
• Advanced serverless workflow patterns and best practices

Conclusion

You can now build extensions for Serverlesspresso, and potentially be featured on the AWS Compute Blog by submitting a Serverlesspresso extension. The best extensions will be added to Serverlesspresso in production.

Some demo extensions have been built and documented at https://github.com/aws-samples/serverless-coffee/tree/main/extensions. You can download and install these extensions to see how they are constructed before creating your own.

Visit the Serverless Workflows Collection to browse the many deployable workflows to help build your serverless applications.