The gym class tracker is a very simple application that can setup a "tracker query" to the REST of a Gym for the availability of a class.

The application is built using a simple serverless setup with Lambda, DynamoDB, SNS and EventBridge Scheduler.

The "tracker query" and its current state are stored in DynamoDB. A Lambda function contains the logic to call the gym API and check if the class of interest is currently available to be booked. For any status changes or errors, a notification is sent to a (fixed) user using SNS. The Lambda Function is called regularly using an Event Bridge Scheduler

This project uses the AWS Serverless Application Model (SAM) and was built using the AWS Toolkit in VSCode.

Folder structure:

• execute-check - Code for the Lambda function executing a check against the gym's API.
• events - Invocation events that you can use to invoke the function.
• tests - Unit tests for the application code.
• template.yaml - A template that defines all the application's AWS resources.
• docs - Diagrams for documentation
• proof-of-concept - First draft of the Lambda function which was originally manually deployed

To build and deploy the application for the first time, run the following in your shell:

sam build --use-container

# this will guide you through installation and prompt for the stack name, AWS region and capability to create IAM roles (to create/modifycIAM roles, the `CAPABILITY_IAM` value for `capabilities` must be set). Arguments can be savet to samconfig.toml
sam deploy --guided

After the first deployment, these comments can be used to deploy changes:

sam build 
sam deploy --parameter-overrides EmailAddress=[enter email address to send notifications] 

Build your application with the sam build --use-container command.

# build: installs dependencies and creates a deployment package in .aws-sam/build
sam build --use-container

Run functions locally and invoke them with the sam local invoke command. Test events are included in the events folder in this project.

sam local invoke ExecuteCheckFunction --event events/empty-call.json

Read logfiles from the deployed Lambda function using the SAM CLI:

sam logs -n ExecuteCheckFunction --stack-name gym-class-tracker --tail

Example for a query in DynamoDB

{
  "partition-key": {
    "S": "query-1"
  },
  "sort-key": {
    "S": "1"
  },
  "entity-name": {
    "S": "check-query"
  },
  "active-status": {
    "S": "1"
  },
  "availability-status": {
    "S": "Unknown"
  },
  "center-id": {
    "S": "23"
  },
  "course-title": {
    "S": "BODYPUMP® 55'"
  },
  "daytime-id": {
    "S": "4"
  },
  "weekday-id": {
    "S": "3"
  }
}

center-id:

• 23 = Zürich Altstetten

daytime-id:

• 1 = morning
• 2 = noon
• 3 = afternoon
• 4 = evening

weekday-id:

• 1 = Monday
• ...
• 7 = Sunday

Delete the deployed application again:

sam delete gym-class-tracker

• AWS SAM developer guide: for an introduction to SAM specification, the SAM CLI, and serverless application concepts.
• AWS Serverless Application Repository main page: Discover, deploy and publish serverless applications

• Split app.py into different files: separate for DynamoDB, API handling and SNS
• Add tests for separate areas
• build additional Lambda CreateTrackerQuery that writes a tracker-query into DynamoDB
• build API Gateway for CreateTrackerQuery
• Secure API Gateway
• Enable different email addresses (maybe move away from SNS for this?)