Developing evolutionary architecture with AWS Lambda

Context

Agility enables you to evolve a workload quickly, adding new features, or introducing new infrastructure as required. The key characteristics for achieving agility in a code base are loosely coupled components and strong encapsulation.

Loose coupling can help improve test coverage and create atomic refactoring. With encapsulation, you expose only what is needed to interact with a service without revealing the implementation logic.

Evolutionary architectures can help achieve agility in your design. In the book “Building Evolutionary Architectures”, this architecture is defined as one that “supports guided, incremental change across multiple dimensions”.

The project is set up to work on eu-west-1, if you want to deploy in another region please change the code accordingly

If you are interested to learn more about this approach, please read the blog post associated to this code example.

Project

This example provides an idea on how to implement a hexagonal architecture with AWS Lambda using Node.js.
The folder structure represents the three key elements that characterizes the first implementation of an hexagonal architecture: ports, adapters and domain logic.

In order to run the project in your AWS account, you have to follow these steps:

1. Download AWS SAM

2. Build the project with the command sam build

3. Deploy the project in your account sam deploy --guided

4. Go to DynamoDB console, add an item to the stock table:

• STOCK_ID: AMZN
• VALUE: 1234.56

5. in the template.yaml add the URL for an API to find the live value of the currencies, it can be as simple as a mock API or a service that provides the live values such as fixer. Independently from the service you want to use, remember the payload response should be structured similar to the following snippet:

{
  "base": "USD",
  "date": "2023-08-22",
  "rates": {
     "CAD": 1.260046,
     "CHF": 0.933058,
     "EUR": 0.806942,
     "GBP": 0.719154
  }
}

After these changes you are able to test the API retrieving the URL from the API gateway console and appending /stock/AMZN

Evolving the project

When we want to evolve the application adding a cache-aside pattern using an ElastiCache cluster for reducing the throughput towards a 3rd party service, we can do it applying some changes to the current architecture.
You can also watch a presentation where I describe the evolutionary nature more in depth.
If you deployed successfully the infrastructure in the previous step, there is only a thing to change. In the ports/CurrenciesService we comment the first import and uncomment the second one. This will use a new adapter called CurrencyConverterWithCache that contains the logic for the cache-aside pattern with ElastiCache Redis cluster

//const getCurrencies = require("../adapters/CurrencyConverter");
const getCurrencies = require("../adapters/CurrencyConverterWithCache");

Thanks to hexagonal architecture we were able to atomically change an adapter and a port without changing anything else in the code base.

Contributing

Please create a new GitHub issue for any feature requests, bugs, or documentation improvements.

Where possible, please also submit a pull request for the change.

License

This library is licensed under the MIT-0 License. See the LICENSE file.