Lecture: Load Balancers in Microservices

Introduction

• Importance of load balancers in distributed systems.
• Essential for handling traffic and ensuring scalability.
• Key concept for deploying applications to production.

Basic Load Balancer Concept

• Avoid single instance access via direct IP due to scalability issues.
• Use load balancers to distribute incoming traffic across multiple instances.

Setting Up Load Balancers

• Start with creating a VM on cloud with a public IP for microservices.
• Problem arises with scaling as the number of clients increases.
• Solution: Multiple replicas of the application (e.g., multiple instances of customer service).

Issues Without Load Balancers

• Clients won't know which instance to connect to, leading to resource imbalance.
• Manually listing all instances and their IPs is impractical.

Introduction of Load Balancers in Architecture

• External Load Balancer: Acts as the main entry point for all client requests.
  • Blocks any direct access to internal instances via firewall.
• Internal Load Balancer: Manages internal communication and traffic distribution among instances.
  • Ensures service-to-service communication is handled efficiently.

Key Considerations for Load Balancers

• SSL/TLS certificate management
• Authentication and TLS termination points
• High availability and cross-region deployment
• Logging, caching, and path-based routing

Managed Load Balancers

• Recommended to use cloud provider-managed load balancers.
  • Examples: Google Cloud Load Balancing, AWS Load Balancer
• Benefits of managed load balancers include auto-scaling, high availability, and integrated features (e.g., SSL management).

Load Balancer Algorithms

• Round Robin: Distributes requests sequentially across servers.
• Least Connections: Sends new requests to the server with the fewest active connections.
• Least Time: Sends requests to the server with the fastest response time.
• Hash: Distributes requests based on a key (e.g., client IP address).
• Random: Uses a random selection process for distributing requests.

Health Checks

• Mechanism to ensure instances are healthy and able to handle requests.
• Different types of health checks:
  • Simple up/down checks based on response status code (e.g., HTTP 200).
  • Database connectivity checks if the service depends on a database.

Summary

• Importance of using load balancers for scalable microservice architectures.
• Introduced key concepts and benefits of external and internal load balancers.
• Discussed different health check mechanisms and load balancing algorithms.

Call to Action

• Engage with the community on Facebook and Discord.
• Enroll in the full course for deeper learning on distributed systems, Kubernetes, Docker, etc.