Serverless Greetings Lab

In this (micro) lab, we're going to build an event-driven Serverless greetings processor. When created, we will have the following architecture in place:

... and we will be able to upload greeting files (samples included in /sample-greetings) for processing by our event-driven application.

For simplicity, the application is written in a single CloudFormation (CFN) template located in serverless-greetings-stack.yml.

Deployment Instructions

To deploy the stack, we have multiple options including the AWS CLI, AWS SDK and the AWS Managment Console.

Using the AWS CLI

aws cloudformation create-stack --stack-name serverless-greetings-stack --template-body file://serverless-greetings-stack.yml --capabilities CAPABILITY_IAM

Docs: https://awscli.amazonaws.com/v2/documentation/api/latest/reference/cloudformation/create-stack.html

Using the AWS SDK for PowerShell

New-CFNStack -StackName serverless-greetings-stack -TemplateBody (Get-Content .\serverless-greetings-stack.yml -Raw) -Capability CAPABILITY_IAM

Docs: https://docs.aws.amazon.com/powershell/latest/reference/items/New-CFNStack.html

Using the AWS Management Console

1. Download the raw serverless-greetings-stack.yml file to your machine
2. Go to the CloudFormation service
3. Select 'Create stack', then select 'With new resources (standard)'
4. Under Prerequisite - Prepare template, select 'Template is ready'
5. Under Specify template, select 'Upload a template file', then 'Choose file'
6. Select the serverless-greetings-stack.yml file downloaded in step 1, then select 'Next'
7. Enter a stack name, i.e., serverless-greetings-stack, then select 'Next'
8. Leave the Configure stack options and Advanced options with their default values, then select 'Next'
9. Finally, in the Review screen, scroll to the bottom and put a checkmark ✔ in: [ ] I acknowledge that AWS CloudFormation might create IAM resources..
10. Select 'Create stack'

The CloudFormation stack is now created and its state is CREATE_IN_PROGRESS. When all resources are created, the state should be: CREATE_COMPLETE.

Tutoral: How To Process Greetings

In the repository, there are a few sample greeting files located in /sample-greetings. Upload some, or all of them, to the greetings S3 bucket created. The name of bucket follows the following pattern:

serverless-greetings-bucket-<AWS_ACCOUNT_ID>-<AWS_REGION>

Example:

serverless-greetings-bucket-123456789012-eu-west-1

When one or more greetings are added to the greetings bucket, Object Created events are emitted (one per object) to EventBridge on the default event bus. In EventBridge, a rule is matched, which sends each event through to the registered target, which is our greeting-processing workflow represented by an AWS Step Functions State Machine.

The state machine looks like this:

The state machine first extracts the object key (filename of the greeting) from the event message we have got from S3 (via EventBridge). The structure of the event emitted by S3 into EventBridge is documented here.

After that, a Choice state is used to check if we have been provided a .txt file or not:

• If we have got a .txt file, the workflow then processes the greeting by invoking the Lambda function ProcessGreeting. This function simply reads the greeting from S3 and stores it in the DynamoDB table (serverless-greetings). When processing of the greeting has completed, the greeting is deleted from S3 by the DeleteGreeting Lambda function.

• On the other hand - if we have been provided with any other file type, i.e., a .json file, we simply short-circuit the workflow and delete the greeting from S3. Deletion of the object is done by the DeleteGreeting Lambda function.

Assuming you have processed greetings as .txt files, you should now be able to see the content of these greetings in the serverless-greetings DynamoDB table (plus a few other attributes added by the ProcessGreeting Lambda function).

This concludes the tutorial.

Clean Up

We use CloudFormation to clean up and remove the resources created in the serverless-greetings-stack:

1. Go to CloudFormation
2. Select the stack (serverless-greetings-stack), then select 'Delete', and confirm by selecting 'Delete stack'
3. CloudFormation now removes all of the resources

Wrapping Up

In this micro lab, we have been playing with a tiny event-driven application powered by Serverless technologies in the AWS Cloud. I hope you have found it interesting to follow along. If you have any input, find bugs, and so on - please feel free to raise an issue or submit a pull-request :)