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docs: improve README clarity and add lambda overview #1

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39 changes: 32 additions & 7 deletions README.md
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Original file line number Diff line number Diff line change
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# velinfo
A serveless application to detect locked Velib stations (Paris' bicycle sharing system).
Hosted on AWS Serveless and visible at https://www.velinfo.fr and [@Velinfo1](https://twitter.com/velinfo1)

[![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](LICENSE)
[![Twitter](https://img.shields.io/badge/follow-@Velinfo1-1DA1F2?logo=twitter&logoColor=white)](https://twitter.com/velinfo1)

A serverless application that detects locked Velib stations (Paris' bicycle sharing system).

Hosted on AWS Serverless and visible at [velinfo.fr](https://www.velinfo.fr) and [@Velinfo1](https://twitter.com/velinfo1).

The raw data comes from the [Velib official API](https://www.velib-metropole.fr/donnees-open-data-gbfs-du-service-velib-metropole). Thanks to them!

## Architecture
## Table of contents
- [Architecture](#architecture)
- [Backend Lambdas](#backend-lambdas)
- [Technical stack](#technical-stack)
- [Build and deploy](#build-and-deploy)
- [License](#license)

## Architecture
![Global Architecture](docs/architecture.png)

The DNS records are managed through Route53.

The frontend application is built with Angular, hosted using a S3 bucket and cached through a Cloudfront Distribution.

The backend consist of several TypeScript Lambdas and Dynamo tables processing data fetched from the Velib API. The resulting data is exposed through an AWS API Gateway.
The backend consists of several TypeScript Lambdas and Dynamo tables processing data fetched from the Velib API. The resulting data is exposed through an AWS API Gateway.

## Backend Lambdas
Each Lambda in `/lambda` has a single responsibility:
- **FetchStationsContent** / **FetchStationsCharacteristics** : periodically pull station availability and characteristics from the Velib API
- **ComputeStationsStates** : detect state changes (e.g. a station becoming locked) from the fetched data
- **ComputeUsage** / **ComputeMedianUsage** : aggregate station activity into usage statistics
- **PublishStateChangeTweet** : tweet about newly detected state changes
- **GetStations** / **GetStateChanges** / **GetActivityByStations** / **GetNetworkActivity** / **GetPredictionByStations** / **GetNetworkPrediction** : API-facing Lambdas that expose the processed data to the frontend

Shared code (Dynamo access, date/type utilities, domain objects) lives in `/lambda/common`.

## Technical stack
- **Languages** : Typescript, both for the backend (AWS Lambda) and the frontend (Angular)
Expand All @@ -34,13 +56,13 @@ What do you need ?
- The AWS SAM CLI
- The Angular CLI

If you want to self host this application, it's possible. But, the SAM template expect a certain number of parameter, mainly regarding the DNS certificates and the Twitter API keys, that are obviously not included in this repo.
If you want to self host this application, it's possible. But the SAM template expects a certain number of parameters, mainly regarding the DNS certificates and the Twitter API keys, that are obviously not included in this repo.
### Backend
```
npm run build
sam deploy
```
The backend code is in the /lambda folder. The infrastructure configuration is defined in template.yml (a SAM template). As TypeScript is not natively supported by SAM, we can't rely on ``sam build``. Instead the build and preparation of the CloudFormation template is done via a custom build command
The backend code is in the `/lambda` folder. The infrastructure configuration is defined in `template.yaml` (a SAM template). As TypeScript is not natively supported by SAM, we can't rely on `sam build`. Instead the build and preparation of the CloudFormation template is done via a custom build command.

### Frontend
```
Expand All @@ -49,4 +71,7 @@ ng build --prod
aws s3 rm s3://velinfo-frontend --recursive
aws s3 cp dist/velinfo s3://velinfo-frontend --recursive --cache-control max-age=31536000
```
The frontend is a standard Angular application which can be built using the [Angular CLI](https://angular.io/cli). Once built, the content need to be pushed to the S3 bucket hosting the static part of the website.
The frontend is a standard Angular application which can be built using the [Angular CLI](https://angular.io/cli). Once built, the content needs to be pushed to the S3 bucket hosting the static part of the website.

## License
This project is licensed under the [MIT License](LICENSE).