Load balancer

• A load balancer sits in front of a group of servers and routes client requests across all of the servers that are capable of handling those requests. Its purpose is to minimize response time and maximize utilization.

• To achieve minimal response time, the load balancer prevents any single server from slowing down the system, distributing the load evenly across multiple servers.

• Maximum utilization is achieved by ensuring that each server in the group is actively handling requests and the workload is evenly distributed.

Fault Tolerance:

• If a server becomes unavailable or goes offline, the load balancer redirects traffic to other available servers.

Automatic Scalling

• When new servers are added to the system, the load balancer automatically includes them in the distribution of incoming requests.

Health Checks:

• Load balancers often perform health checks on individual servers to assess their availability and performance.
• If a server is found to be unhealthy, the load balancer stops directing traffic to that server until it recovers.

How the project works ?

• You have 5 "Express" servers and a "load balancer" sitting infront of them.
  

• This command "curl http://localhost:LOAD_BALANCER_PORT" calls the load balancer, then the load balancer will forward that request to servers according to RR (Round Robin) algorithm:
  

• 1st request => 1st server
  

• 2nd request => 2nd server
  

• 3rd request => 3rd server
  

• 4th request => 4th server
  

• 5th request => 5th server
  

• 6th request => 1st server
  

• ....

How to run the project on your machine ?

• Clone the repository

• npm install

• Generate ".env" file and allocate these variables to unused ports on your local machine:
  

  • LOAD_BALANCER_PORT=
  • SERVER-1_PORT=
  • SERVER-2_PORT=
  • SERVER-3_PORT=
  • SERVER-4_PORT=
  • SERVER-5_PORT=

• npm run dev

• Once you run the command "npm run dev". All the servers get started and the load balancer will be listening on the port you allocated in the ".env" file.

• When you send an HTTP request to the load balancer by:
  

  • curl http://localhost:LOAD_BALANCER_PORT/
    

• It will forward the request to the active servers and you will get message from server according to RR algorithm.

  • Request successfully processed by server: http://localhost:3003

• This command checks the health of the server and provides a response containing details about it:
  

  • curl http://localhost:LOAD_BALANCER_PORT/health-check
    

• To stop any server, you can use the following command:

  • curl http://localhost:LOAD_BALANCER_PORT/stop/server_index
  • For example-> curl http://localhost:8000/stop/2
    • And when you send a request to that server, then it will respond with Server http://localhost:3002 did not respond. Trying the next server.

• And to stop the health check, you can use the following

  • curl http://localhost:LOAD_BALANCER_PORT/shutdown

• So, if all servers are down, then any request sent to the load balancer will send an error response

  • "error":"All servers failed to respond"

Docker Setup Instructions

To use Docker for your web app, follow these simple steps:

1. Install Docker If you haven't already installed Docker, you can download and install it from the official website: Docker Website

2. Build Docker Image Navigate to the root directory of your web app where the Dockerfile is located and run the following command to build your Docker image:

docker build -t my-web-app 

Replace my-web-app with a suitable name for your Docker image.

3. Run Docker Container Once the Docker image is built, you can run a Docker container using the following command:

docker run -d -p 8000:8000 --name my-web-app-container my-web-app

Replace 8000 with the port number your web app is running on, and my-web-app-container with a suitable name for your Docker container.

4. Access Your Web App You can now access your web app by navigating to http://localhost:8000 in your web browser.