Mastering High Availability and Load Balancing in Cloud Computing

Course Overview

U创营 is a cloud‑computing popular‑science series designed for university students, offering video explanations, illustrated text, and hands‑on practice to bridge theory and practice and help learners acquire basic employable skills.

Course Content

High Availability and Load Balancing

High‑availability (HA) systems are deliberately designed to minimize downtime and keep services highly available, which is crucial in production. Common HA approaches include active‑active and active‑standby configurations, each with its own advantages, while more complex scenarios may employ HA clusters.

Load balancing satisfies the need for both high availability and traffic distribution. The field has a long history with many well‑known commercial (closed‑source) products offering high performance and stability at a premium, as well as open‑source alternatives that are free and customizable but require self‑maintenance.

Innovations such as Intel DPDK (Data Plane Development Kit) have dramatically increased data‑plane performance and throughput, even on inexpensive hardware.

Ideally, cloud‑provider load‑balancer products should combine the strengths of both commercial and open‑source solutions to deliver ultra‑high performance, stability, low cost, and reduced operational effort.

Load Balancer Features and Scenarios

Using UCloud’s ULB as an example, the service supports both Layer‑4 and Layer‑7 protocols. For HTTPS traffic, dedicated SSL hardware offloading can significantly boost performance. ULB consists of VServer (virtual server) that defines the service purpose and port, and BServer (backend server) that specifies the actual node configuration.

Key technical points include health checks, session persistence, and scheduling algorithms.

Health Checks : Continuously verify backend node availability; Layer‑7 checks use HTTP, while Layer‑4 checks test port reachability.

Session Persistence : Ensure a user's requests are routed to the same backend node; achieved via cookies at Layer‑7 or IP address at Layer‑4.

Scheduling Algorithms : Distribute traffic based on rules such as round‑robin, least connections, or consistent hashing. Consistent hashing maintains efficiency while minimizing system disruption.

Combining load balancing with availability zones yields higher HA. Cross‑zone cloud deployment is recommended because it offers good affinity, avoids usage obstacles, and fiber connections ensure low‑latency internal networking.

High‑Availability Virtual IP

Virtual IPs in private networks are a typical active‑standby HA usage, often implemented with protocols like VRRP. They ensure consistent external service addresses, provide heartbeat detection, and enable automatic failover.

VIP products use GARP to announce the address for both cloud and physical hosts, allowing second‑level failover and rapid recovery to protect core business services.