Serverless Transcription App

Key	Value
Environment
Services	Transcribe, S3, Lambda, SQS, SES
Integrations	Serverless Framework, AWS CLI, Serverless Lift Pluglin, AWS SDK
Categories	Serverless, Event-driven architecture, S3 Trigger, LocalStack developer endpoints
Level	Intermediate
Github	Repository link

Introduction

The Transcription sample application simplifies and streamlines the process of transcribing audio files. This sample application allows you to upload your audio files and receive a transcript in minutes.

The sample application exposes a user-friendly web interface that allows you to upload audio files and view completed transcription jobs in an S3 bucket with an email triggered via SES to notify you of the job completion. You can further view a list of all your completed transcription jobs and a link to download the transcription JSON file. Users can deploy this application setup via the Serverless Framework on LocalStack.

To test this application sample, we will demonstrate how you use LocalStack to deploy the infrastructure on your developer machine and your CI environment and invoke the transcription job on your local machine.

Architecture diagram

The following diagram shows the architecture that this sample application builds and deploys:

We are using the following AWS services to build our infrastructure:

• Lambda to serve the frontend and process the audio file.
• Transcribe to convert the audio file into a transcription JSON file.
• S3 to store the audio file and the transcription JSON file.
• SES to send an email notification to the end user.

Prerequisites

• LocalStack Pro with the localstack CLI.
• AWS CLI with the awslocal wrapper.
• Serverless Framework with Serverless LocalStack Plugin and Serverless Lift Plugin
• Node.js with npm package manager.

Start LocalStack Pro with the LOCALSTACK_AUTH_TOKEN pre-configured:

export LOCALSTACK_AUTH_TOKEN=<your-auth-token>
localstack start

If you prefer running LocalStack in detached mode, you can add the -d flag to the localstack start command, and use Docker Desktop to view the logs.

Instructions

You can build and deploy the sample application on LocalStack by running our Makefile commands. Run make deploy to create the infrastructure on LocalStack. Run make stop to delete the infrastructure by stopping LocalStack.

Alternatively, here are instructions to deploy it manually step-by-step.

Install the dependencies

We use the Serverless Framework to deploy the sample application. Install the Serverless Framework and other dependencies by running the following commands:

npm install -g serverless
npm install

Deploy the infrastructure

We will use the serverless deploy command to deploy the infrastructure. This command will create the required resources on LocalStack. Run the following command to deploy the infrastructure:

sls deploy --stage local --verbose

The --stage flag is specified to deploy the infrastructure to the local stage. It sets up Serverless to use the LocalStack plugin but only for the stage local to deploy the infrastructure to LocalStack only.

After a few seconds, the infrastructure should be deployed successfully. You will find a LocalStackSampleAppEndpoint URL specified in the output. This URL is the endpoint for the frontend application and should look similar to: https://vmvs1am212p.execute-api.localhost.localstack.cloud:4566/local/upload.

Next, we need to create configurations for CORS settings for our S3 bucket and verification for SES:

awslocal s3api put-bucket-cors --bucket aws-node-sample-transcribe-s3-local-records  --cors-configuration file://etc/cors.json
awslocal s3api put-bucket-cors --bucket aws-node-sample-transcribe-s3-local-transcriptions  --cors-configuration file://etc/cors.json
awslocal ses verify-email-identity --email-address sender@example.com

Testing the application

Navigate to the LocalStackSampleAppEndpoint URL specified in the output of the sls deploy command. When accessing the webpage the first time, it will take a few seconds to load. You should see a web page similar to the following:

Click on the Upload button to upload a file. You can choose one of the files from the sample-audio-files folder, which will then be uploaded to the designated S3 bucket (aws-node-sample-transcribe-s3-local-records).

Note: The upload will take a few seconds for the first time, subsequent uploads will be faster, because the Lambda is already warm.

Allow the Lambda function (aws-node-sample-transcribe-s3-local-transcribe) to process the uploaded file. The Lambda function will create a transcription job with the record uploaded in the previous step and push the resulting output JSON file to an S3 bucket (aws-node-sample-transcribe-s3-local-transcriptions).

Upon completion of the file processing, the user interface will display the transcription output. Click the List all jobs button to view it. You might need to reload the page, if it is not visible yet.

The transcription can be downloaded by selecting the jobname.json hyperlink. To verify that the email has been sent correctly, use the internal LocalStack SES endpoint at http://localhost.localstack.cloud:4566/_aws/ses.

Using SMTP Integration

LocalStack Pro supports sending messages through an SMTP email server. To test this feature, you could use a mock SMTP server, like smtp4dev or Papercut SMTP to receive the email notifications locally.

For example, when using smpt4dev start the SMTP server using:

docker run --rm -it -p 3000:80 -p 2525:25 rnwood/smtp4dev

You can then access the web interface on http://localhost:3000 where you will see any incoming messages. Then start LocalStack with the SMTP_HOST environment variable, pointing to the host and port where the SMTP server is reachable:

export LOCALSTACK_AUTH_TOKEN=<your-auth-token>
SMTP_HOST=host.docker.internal:2525 localstack start

If you are using a real SMTP server, you will also need to set the env for SMTP_USER and SMTP_PASS).

Following the instructions of the deployment above. The emails will show up in the web UI.

GitHub Actions

This application sample hosts an example GitHub Action workflow that starts up LocalStack, builds the Lambda functions, and deploys the infrastructure on the runner. You can find the workflow in the .github/workflows/main.yml file. To run the workflow, you can fork this repository and push a commit to the main branch.

Users can adapt this example workflow to run in their own CI environment. LocalStack supports various CI environments, including GitHub Actions, CircleCI, Jenkins, Travis CI, and more. You can find more information about the CI integration in the LocalStack documentation.

Contributing

We appreciate your interest in contributing to our project and are always looking for new ways to improve the developer experience. We welcome feedback, bug reports, and even feature ideas from the community. Please refer to the contributing file for more details on how to get started.