somod-docs/src/reference/main-concepts/serverless/functions.md

Documentation for SOMOD

```YAML
title: Serverless Functions in SOMOD Module | SOMOD
meta:
  description:
    Develop, build and deploy serverless functions with ease using SOMOD modules.
```

# Serverless Functions

---

The `serverless/functions` directory contains the code for Lambda functions. The developer first creates the lambda resource in the `template.yaml`, then adds a typescript file containing code under the functions directory. The lambda resource in the `template.yaml` must have a reference to the filename of the corresponding function.

> When AWS invokes the lambda, it passes an event to the handler function and waits for the returned promise to complete. The contents of the event object and response depend on the use of lambda. This [AWS Documentation](https://docs.aws.amazon.com/lambda/latest/dg/lambda-services.html) describes the different ways of invoking the lambda function.  
> The event and response types are available from the [`@types/aws-lambda`](https://www.npmjs.com/package/@types/aws-lambda) package.

Every SOMOD function must have a lambda handler as the default export.
The SOMOD prepare command will generate a javascript bundle capable of running inside nodeJs runtime at the `.somod/serverless/functions/{moduleName}/{functionName}` directory.

SOMOD excludes the npm packages in the attached layers from the function bundle.

By default, the lambda functions are bundled for NodeJs version 18. bundle for a different version of NodeJs by setting `SOMOD_SERVERLESS_NODEJS_VERSION` environmental variable before calling `somod prepare` command.

## Layers

The developer can add common libraries used across multiple functions in a layer. Refer `SOMOD::Function` and `SOMOD::FunctionLayer` keywords in [serverless/template.yaml](/reference/main-concepts/serverless/template.yaml) for syntax.

## Invoking the functions

AWS SAM documentation describes the [event sources](https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/sam-property-function-eventsource.html) to configure the invocation of the function.

The lambda function can handle any of the events described in the _event sources_ and more. In a SOMOD Module, each lambda function must handle only one type of event and the same should match the `type` property of `SOMOD::Function` keyword in [serverless/template.yaml](/reference/main-concepts/serverless/template.yaml)

For [HttpApi](https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/sam-property-function-httpapi.html) and [Api](https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/sam-property-function-api.html) event sources SOMOD automatically tries to resolve the conflicting API Routes.
For conflict resolution strategy, refer to [Namespaces](/reference/main-concepts/namespaces).

## Debug

By default, functions are bundled and minified when prepared. Enable `--debug` flag with `somod prepare` command to keep the functions un-minified along with source-map enabled in the deployed lambda function.

## Extending the functions

Replace the whole lambda function code in a dependent module by Extending the function resource and proving the new code to `SOMOD::Function`.

Or

Wrap the function with the middleware using SOMOD's middleware framework.

In the [next chapter](/reference/main-concepts/serverless/middlewares), let us dive into the concept of middleware in SOMOD.