---
categories:
  - DevOps
  - Backend
tags: [AWS]
---

# AWS SAM

SAM stands for **serverless application model**. It is a framework developed by AWS to simplify the process of building, deploying and managing serverless applications. It provides a concise syntax for defining the components of a serverless application, such as [Lambda functions](/DevOps/AWS/AWS_Lambda/Lambda_programming_model.md), [API gateway](/DevOps/AWS/AWS_API_Gateway.md) and database tables.

The SAM infrastructure is defined in a YAML file which is then deployed to AWS. SAM syntax gets transformed into CloudFormation during the deployment process. (CloudFormation is a broader and more robust AWS tool for large, highly scaleable infrastructures).

## Key features of SAM

- Single deployment configuration
- Integration with development tools
- Local testing and debugging
- Built on AWS CloudFormation

## Main technologies required

### Docker

Whilst SAM can be used to create a deployable file for AWS it can also be run as a container for local development with Docker.

### AWS CLI

This is installed using Python and allows you to interact directly with AWS via the command-line.

### AWS SAM CLI

See [https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/install-sam-cli.html](https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/install-sam-cli.html)

## Setting up credentials for the AWS CLI

```
aws configure
AWS Access Key ID [None]: AK*******
AWS Secret Access Key [None]: ukp******
Default region name [None]:
Default output format [None]:
```

This information can be found in the Security Credentials section of the given [IAM](/DevOps/AWS/AWS_User_management_and_roles.md#iam) user:

![](/_img/access-key-aws.png)

## Starting a SAM project

First create a directory for your project which will serve as the repository:

```sh
mkdir aws-sam-learning
cd aws-sam-learning
```

Then we can use the `sam` cli to bootstrap the project:

```sh
sam init --runtime nodejs16.x
```

We can just click through and accept the basic HelloWorld Lambda.

This will create the Lambda as well as an API Gateway trigger URL.

### `template.yaml`

This is autogenerated and details the main constituents of the project. There are lots of fields but the most important are the following:

```yaml
HelloWorldFunction:
  Type: AWS::Serverless::Function
  Properties:
    CodeUri: hello-world/
    Handler: app.lambdaHandler
    Runtime: nodejs16.x
    Architectures:
      - x86_64
    Events:
      HelloWorld:
        Type: Api
        Properties:
          Path: /hello
          Method: get
```

This details the location of the [handler function](/DevOps/AWS/AWS_Lambda/Lambda_handler_function.md) which is contained at the path `hello-world/app.js`:

```js
exports.lambdaHandler = async (event, context) => {
  try {
    // const ret = await axios(url);
    response = {
      statusCode: 200,
      body: JSON.stringify({
        message: "hello world",
        // location: ret.data.trim()
      }),
    };
  } catch (err) {
    console.log(err);
    return err;
  }

  return response;
};
```

It also lists the `get` event that we can use to call API Gateway and trigger the Lambda.

The full template is below:

![](/_img/sam-template-yaml.png)

## Adding our own code

We will create our own function and API Gateway trigger.

We will place our function after the existing `HelloWorldFunction`

```yaml
ClockFunction:
  Type: AWS::Serverless::Function
  Properties:
    CodeUri: clock/
    Handler: handler.clock
    Runtime: nodejs16.x
  Events:
    ClockApi:
      Type: Api
      Properties:
        Path: /clock
        Method: get
```

Just like with `HelloWorld`, we will create a directory for this function: `clock` and we will initialise it as an `npm` project.

```sh
mkdir clock
cd clock
npm init
```

We will use `handler.js` as our root, handler function.

We have said in the template file that our `Handler: handler.clock`, therefore the main function in the `handler` module should be `clock`:

```js
const moment = require("moment");

exports.clock = async (event) => {
  console.log("Clock function run");
  const message = moment().format();
  const response = {
    statusCode: 200,
    body: JSON.stringify(message),
  };
  return response;
};
```