Store Thumbnails from Your Live Stream Using AWS SAM CLI to Set Up Lambda Function and API Gateway

Fatma Sena Ekiz — Thu, 20 Apr 2023 22:50:51 +0000

The AWS SAM Command Line Interface (CLI) lets you locally build, test, and debug serverless applications defined by AWS SAM templates. The SAM CLI provides a Lambda-like execution environment locally and helps you catch issues upfront by providing parity between the actual Lambda execution environment.

NOTE: This repository contains the code you will implement, so you can apply the steps and configure your own SAM project by copying and changing the content in your SAM template project with the code in this folder.

Step 0 - Install AWS SAM CLI

Complete all prerequisites before moving forward with installing AWS SAM CLI. This includes:

Signing up for an AWS account.
Creating an administrative IAM user.
Creating an access key ID and secret access key.
Installing the AWS CLI.
Configuring AWS credentials.

Then, follow this tutorial to install AWS SAM CLI. Then, create a sample Hello World application to start with a project template. Choose the options below to configure a project from the CLI.

After configuring your project, it will come with a template.yaml file that contains a Lambda function called HelloWorldFunction and an API event. Navigate through your project and open it in a code editor.

Step 1- Edit the Lambda Function and Create an API Gateway

We need to update the template.yaml by adding a new API and reference it under the API events.

Add this code block under your Resources:

MyApi:
    Type: AWS::Serverless::Api
    Properties:
      StageName: Prod
      BinaryMediaTypes:
      - image/jpeg

And, reference it under Events like this:

Events:
        HelloWorldApi:
          Type: Api
          Properties:
            RestApiId: !Ref MyApi
            Path: /hello
            Method: POST

Remove the ApplicationResourceGroup and Outputs part. Your template.yaml file should look like this at the end (Description part is same with how you specify your project's name during installation, so it may be different in your project):

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: >
  blog-aws-sam-thumbnails

  Sample SAM Template for blog-aws-sam-thumbnails

# More info about Globals: https://github.com/awslabs/serverless-application-model/blob/master/docs/globals.rst
Globals:
  Function:
    Timeout: 3

Resources:
  MyApi:
    Type: AWS::Serverless::Api
    Properties:
      StageName: Prod
      BinaryMediaTypes:
      - image/jpeg
  HelloWorldFunction:
    Type: AWS::Serverless::Function # More info about Function Resource: https://github.com/awslabs/serverless-application-model/blob/master/versions/2016-10-31.md#awsserverlessfunction
    Properties:
      CodeUri: hello-world/
      Handler: app.lambdaHandler
      Runtime: nodejs18.x
      Architectures:
        - x86_64
      Events:
        HelloWorldApi:
          Type: Api
          Properties:
            RestApiId: !Ref MyApi
            Path: /hello
            Method: POST

Step 2 - Deploying the SAM project

Let's test if we can successfully set up our Lambda Function and API Gateway. For the purpose of this walkthrough, we'll simply log the payload of the received event to the console and return a 200 status code back to the source to indicate successful reception. In the next steps will implement the code to actually handle the call.

Go to app.mjs under hello-world folder and add a console.log(event). Your app.mjs should look like:

export const lambdaHandler = async (event, context) => {
    try {
        console.log(event)
        return {
            'statusCode': 200,
            'body': JSON.stringify({
                message: 'hello world',
            })
        }
    } catch (err) {
        console.log(err);
        return err;
    }
};

Then, go to root of your project (where template.yaml is available) and run sam build in your terminal. After you get Build Succeeded notification, run sam deploy --guided Say yes(Y) to deployment wizard's prompts as shown below:

Once you get Successfully created/updated stack ... navigate through your API Gateway and Stages in your AWS Console and copy the "Invoke URL" in the "Prod" stage.

Now, you can use the "Invoke URL" as a webhook URL by adding the /hello Path to the end, as defined in your template.yaml when setting up the API gateway. So, for example, your webhook URL should be:

https://23k6og5dc1.execute-api.us-west1.amazonaws.com/Prod/hello

Step 3 - Set Up Dolby.io to Test the Webhook

To create a token on your Dashboard go to https://streaming.dolby.io/#/tokens and click Create button. After you set the Basic settings, you need to enable Thumbnail Preview from the Advanced settings.

To create a webhook on your Dashboard go to https://streaming.dolby.io/#/webhooks and click Create button. You need to enable Thumbnail hooks and add the Webhook URL that you got from the previous step.

Step 4 - Handling the Event and Storing the Thumbnails in an S3 Bucket

After successfully seeing the log of the event in the "CloudWatch", we are now ready to implement the functionality to handle the event to compare signatures and upload the thumbnail image to the created S3 bucket.
→ First, replace the entire app.mjs file in your project with the code in the app.mjs file.

→ Then navigate through your hello-world folder directory --- the directory that contains the Lambda function --- and type npm install crypto util aws-sdk to install the packages that our code uses. Save your code and go back to the root directory of your project where the template.yaml exists.

→ Next, we need to create an S3 bucket. From your AWS Management Console search S3, from Buckets click 'Create Bucket' and set a name for your bucket.

(We used the name blog-thumbnails-bucket for the sample code in this repository.)

Then, use services search bar for IAM, and go to Policies under IAM Dashboard. Click Create Policy and from Visiual editor choose a Service as S3. From Actions, choose PutObject to specify actions allowed in S3. And for Resources, click Add ARN(s) and enter the 'Bucket name' and select 'Any' for 'Object name' and click 'Add'. Select a name for your policy on the 'Review policy' part and click 'Create policy' button. Lastly, from IAM Roles menu, find your Lambda function and from 'Add Permission' button, click 'Attach Policies' and find the policy you created and click 'Add Permissions'.

Watch how to apply the previous steps to set up an S3 bucket

→ Now, we need to add the WEBHOOK_SECRET as an environment variable to our Lambda function. Go to the Dolby.io Dashboard and click on the webhook you created, copy the Webhook Secret. Navigate to the AWS Lambda Console Configuration menu and add an environment variable called WEBHOOK_SECRET.

Before you deploy the project, go to your samconfig.toml and change the 'resolve_s3' parameters (lines 23 and 32) to 'false' in your project.

→ Now that we've set up an S3 bucket, updated our Lambda function code accordingly, and added the WEBHOOK_SECRET as an environment variable --- we are good to run sam build and sam deploy in our terminal.

TEST TIME!!!

Now, go back to your Dolby.io dashboard and start a Broadcast. Then, navigate back to your lambda function's "CloudWatch logs". You should be receiving an event log every 30 seconds, and check your S3 bucket and view the logged image objects.