On a whiteboard, design a three server web infrastructure that hosts the website www.foobar.com. Requirements: You must add: 2 servers 1 web server (Nginx) 1 application server 1 load-balancer (HAproxy) 1 set of application files (your code base) 1 database (MySQL) You must be able to explain some specifics about this infrastructure: For every additional element, why you are adding it What distribution algorithm your load balancer is configured with and how it works Is your load-balancer enabling an Active-Active or Active-Passive setup, explain the difference between both How a database Primary-Replica (Master-Slave) cluster works What is the difference between the Primary node and the Replica node in regard to the application You must be able to explain what the issues are with this infrastructure: Where are SPOF Security issues (no firewall, no HTTPS) No monitoring Please, remember that everything must be written in English to further your technical ability in a variety of settings.

Step 1: Designing the Infrastructure

First, let's draw the three servers on the whiteboard.

• Server 1: This is our web server where we will install Nginx. Nginx is a popular open-source web server that is known for its high performance and stability. It will be responsible for serving static content and forwarding dynamic content requests to the application server.

• Server 2: This is our application server where our application files (code base) will reside. The application server is responsible for running our application logic and interacting with the database.

• Server 3: This is our database server where we will install MySQL. MySQL is a widely used open-source relational database management system. It will store and manage all the data needed by our application.

In front of these servers, we will place a load balancer (HAproxy). The load balancer is responsible for distributing incoming network traffic across the servers to ensure no single server becomes overwhelmed with too much traffic. This helps to increase the availability and reliability of our application.

Step 2: Explaining the Specifics

• Load Balancer: We are adding a load balancer to distribute the load among our servers and prevent any single server from becoming a bottleneck. We can configure our load balancer with a round-robin distribution algorithm, which works by distributing client requests evenly across all servers in the pool.

• Active-Active vs Active-Passive: In an Active-Active setup, all servers are running and handling traffic. In an Active-Passive setup, one server is active and handling traffic, while the other is a standby server that only becomes active if the primary server fails. Our load balancer is enabling an Active-Active setup to maximize resource utilization.

• Database Primary-Replica (Master-Slave) Cluster: In this setup, the primary node (master) handles all write operations and propagates the changes to the replica nodes (slaves). The replica nodes can handle read operations. This setup helps to distribute the database load and increase data availability.

• Primary Node vs Replica Node: The primary node is responsible for handling write operations, while the replica node is responsible for handling read operations. From the application's perspective, it can write data to the primary node and read data from either the primary or replica nodes.

Step 3: Identifying the Issues

• Single Point of Failure (SPOF): If any of our servers (web, application, or database) or the load balancer fails, it could cause our entire application to become unavailable.

• Security Issues: Without a firewall, our servers are exposed to potential attacks. Without HTTPS, the data transmitted between our servers and clients is not encrypted and could be intercepted.

• No Monitoring: Without a monitoring system in place, we won't be able to detect issues or anomalies in our infrastructure in a timely manner.