Load Balancer

This is a load balancer. I build it for learning purposes, part of the coding challenges from https://codingchallenges.fyi/

Description

The load balancer balances load between configured servers using least connections method. It performs a periodic health check on configured servers, healthy servers are prefered to unhealthy servers when delegating requests. Health checks are performed by firing an http GET request for / to each server, if a server responds with a status code outside the range from 200 to 399, the health check fails. It also allows to register, delete, and modify servers through an http api, and a simple command line interface.

Components

• Balancer

  • contains server configurations
  • exposes an api to manipulate server configs
  • fires a health checks service to monitor and report servers' health
  • balances between incoming requests using least connections method and server weights

• HTTP API

  • used to manipulated server configs
  • it uses an http endpoint to accept requests
  • available endoints are:

    • POST 127.0.0.1:API_PORT/add

      • request body:

        {
          "url": "string",
          "name": "string",
          "weight": "uint32",
          "health_check_period": "uint32"
        }

    • POST 127.0.0.1:API_PORT/delete

      • request body:
        • server_url

    • POST 127.0.0.1:API_PORT/update

      • request body:

        {
          "url": "string",
          "name": "string",
          "weight": "uint32",
          "health_check_period": "uint32"
        }

• Health Check Service

  • spawns a separate health check thread for each server.
  • listens and reacts to modifications in monitored servers, so a new health check thread will be spawned for newly added servers, deleted servers will have their threads aborted, and health check periods for current servers should be reflected if modified.

• CLI

  • the app exposes a cli to interact with the balancer
  • available commands:
    • listen:
      • starts the load balancer with the specified configurations
      • command arguments:
        • --config: specified the path of a yaml file which contains servers configurations
        • --port: this is the load balancer's port. incoming requests on this port will be delegated to the suitable server. defaults to 80
        • --api-port: this is the api port for the load balancer: requests to modify server configs will be accepted on this port. defaults to 8000
        • --debug: enable debug logging
    • add-server:
      • adds a new server to the load balancer
      • command arguments:
        • --url: server url, has to be unique.
        • --name: server name
        • --weight: server weight, higher values result in more requests delegated to this server. defaults to 1
        • --health-check-period: balancer will perform a health check on this server each specified period. defaults to 10
        • --api-port: balancer's api port. defaults to 8000
    • delete-server:
      • deletes a monitored server
      • command arguments:
        • --url: server url
        • --api-port: balancer's api port: defaults to 8000
    • update-server:
      • updates a currently monitored server
      • command arguments:
        • --url: server url, has to be already added.
        • --name: server name
        • --weight: server weight, higher values result in more requests delegated to this server. defaults to 1
        • --health-check-period: balancer will perform a health check on this server each specified period. defaults to 10
        • --api-port: balancer's api port. defaults to 8000