Explorer-Sync

Nestjs monorepo microservices that access the Lum Network Client and fetches recent blocks. It is intended to be a lightweight version of the explorer api.

Architecture

Acceptance Criterias

• Fetch last X blocks
• Show a given block by its height
• Fetch transactions for a given block
• Show a given transaction by its hash

NB: For the purpose of this exercice, we only return the 100 last fetched blocks.

Description

The monorepo provides 3 services:

• One block-sync services to sync blocks from lumClient
• One explorer service to insert and expose v1/explorers/blocks api
• One NoSQL database to persist the last fetched blocks

Features

1. block-sync service (Dockerized):

• Scheduler that fetches the last 20 blocks every 30 seconds
• Processor functionality for the Rabbit-MQ queue
• Caching (ttl 60 seconds) functionality to filter out duplicates in order to emit only sequential blocks to explorer service

2. explorer service (Dockerized)

• Consumer functionality for the Rabbit-MQ queue
• Verifies if the DB does not contain more than 100 documents before inserting a new one (100 serves as a demo for the purpose of this exercise)
• Exposes api endpoint for clients to expose following informations:

{
  "_id": string,
  "blockHeight": number,
  "blockTx": number,
  "txHashes": array of strings,
  "timestamp": utc timestamp
}

NB: By operating requests on lumClient no blockTx and txHashes could be found so far, resulting in 0 and empty array of strings.

• Swagger doc available on port 3001/api
• Versoning has been implemented and defaults to v1
• Caching has been implemented and defaults to a ttl of 60 seconds
• Rate limiting has been implemented to protect against ddos
• Security best practices such as helmet or cors are available on the main root level
• Filters, interceptors and guards have been implemented
• Availability on get /v1/explorers/blocks?limit=xx:
• Authorization key below:

Authorization: cDQnu1vC1Ad29ZUtOhrj

3. NoSQL database (Dockerized common library service)

• MongoDB as NoSQL
• Mongoose as ODM

Installation

Developers node version
v12.13.0

$ git clone https://github.com/Ricardo-Remy/explorer-sync.git

$ npm install

Running the app

Make sure you have docker installed.

# development
$ docker-compose up --build -V

Wait a couple of minutes for the services to build and to start receiving the first events (you will see them logged in your terminal).

In a separate terminal window you can run the tests.

# unit tests
$ npm run test

Tech stack choices

For the purpose of this exercice, 4 main technical decisions have been taken:

• Use Nestjs as a progressive Nodejs framework. The 3 reasons are:

  • Strongly typed
  • Opinionated architecture which facilitates scalability
  • Active codebase development and maintenance

• Use microservices with monorepo approaches to enforce loose coupling between services

• Rabbit-MQ as a message broker. The 3 reasons are:

  • Message durability
  • Message acknowledgment
  • Can be configured to use SSL

• Use a NoSQL database. The 3 reasons are:

  • The access pattern is defined
  • We don't need to perform flexible or relational queries in this project context
  • Low latency and high speed availability to retrieve documents

What this app does not contain

• Github actions
• e2e tests and other extensive test cases

NB: Happy to discuss during the code feedback session.

License

Nest is MIT licensed.

explorer-sync