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Community Blog Mastering Alibaba Cloud Load Balancing: SLB, ALB, NLB, and Classic CLB

Mastering Alibaba Cloud Load Balancing: SLB, ALB, NLB, and Classic CLB

This article explores Alibaba Cloud’s load balancing solutions—SLB, ALB, NLB, and CLB—and their roles in optimizing traffic management for various digital environments.

Recently, I have been working out a solution regarding service open to the public with 7 x 24 services uptime requirement, as one of the lesson learnt, end users may confuse or struggle between Load Balance, this is one of the reasons I would like to write up a Blog for mastering this.

In the era of global digital transformation, efficiently managing application traffic is pivotal for scalability, resilience, and seamless user experiences. Alibaba Cloud, a leader in cloud innovation, provides a robust suite of load balancing solutions tailored to diverse workloads. They are Server Load Balancer (SLB), Application Load Balancer (ALB), Network Load Balancer (NLB) and Classic Load Balancer (CLB), let us explore one by one!

1. Server Load Balancer (SLB)

It serves as the cornerstone of traffic distribution, supporting both Layer 4 (TCP/UDP) and Layer 7 (HTTP/HTTPS) protocols. Designed for versatility, SLB ensures high availability and fault tolerance across Elastic Compute Service (ECS) instances, containers, and hybrid cloud deployments.

Key Features:

  • Seamlessly distributes traffic across multiple availability zones for disaster recovery.
  • Integrates with Auto Scaling to dynamically adjust resources during traffic spikes.
  • Offers SSL/TLS termination, reducing backend server overhead.
  • Ideal for monolithic applications or simple web services requiring basic load balancing.

Use Case: A regional e-commerce platform handling steady HTTP/HTTPS traffic with SSL offloading.

2. Application Load Balancer (ALB)

It is engineered for microservices and API-driven ecosystems, operating at Layer 7 (HTTP/HTTPS). It enables granular routing based on:

• URL paths (e.g., /payments vs. /inventory).

• Host headers (e.g., api.company.com vs. portal.company.com).

• HTTP methods (GET, POST) or cookie-based sessions.

Key Features:

  • Native support for WebSocket, HTTP/2, and QUIC protocols.
  • Advanced traffic management with redirects, rewrites, and fixed responses.
  • Tight integration with Alibaba Cloud WAF (Web Application Firewall) and Function Compute for serverless backends.
  • Real-time monitoring via Alibaba Cloud’s Log Service and ARMS (Application Real-Time Monitoring Service).

Use Case: A containerized application on ACK (Alibaba Cloud Container Service) requiring path-based routing to microservices.

3. Network Load Balancer (NLB)

It is built for latency-sensitive, high-throughput workloads. Operating at Layer 4 (TCP/UDP), it delivers single-digit millisecond response times, making it perfect for gaming, IoT, and financial trading platforms.

Key Features:

  • Supports static IPs and Anycast EIPs for global traffic acceleration.
  • Handles millions of concurrent connections with ultra-low latency.
  • Preserves source IP addresses for backend auditing and security policies.
  • Seamlessly scales during traffic surges, such as live-streaming events or flash sales.

Use Case: A global gaming platform requiring real-time interaction across regions with 10M+ concurrent users.

4. Classic Load Balancer (CLB)

It is Alibaba Cloud’s legacy solution, supporting basic Layer 4 and Layer 7 distribution. While largely succeeded by ALB and NLB, it remains in use for older systems or specific compliance requirements.

Key Features:

  • Basic HTTP/HTTPS and TCP load balancing.
  • Compatible with ECS Classic instances (phased out in newer architectures).
  • Limited advanced routing capabilities compared to ALB/NLB.

Use Case: Migrating legacy on-premises applications to the cloud with minimal re-architecture.

How we choosing the A Right Alibaba Cloud Load Balancer?

• ALB: Modern web apps, microservices, or API gateways needing intelligent Layer 7 routing.

• NLB: High-frequency trading, real-time analytics, or UDP-based workloads (e.g., VoIP).

• SLB/CLB: Simple applications or legacy systems (prioritize migration to ALB/NLB for scalability).

What situation is considered Alibaba Cloud:

Global Infrastructure: Leverage 89 availability zones across 30 regions, optimized for Asia-Pacific and emerging markets.

Hybrid Cloud Support: Integrate on-premises data centers with SLB for unified traffic management.

Security: Built-in DDoS protection, TLS 1.3 support, and compliance certifications (e.g., GDPR, ISO 27001).

Cost Efficiency: Pay-as-you-go pricing with no upfront commitments, ideal for variable workloads.

Insights:

Alibaba Cloud’s load balancing portfolio empowers businesses to future-proof their architectures, whether deploying AI-driven apps, hyperscale platforms, or hybrid cloud solutions. By aligning workload’s demands with ALB’s precision, NLB’s speed, or SLB’s flexibility, achieve unmatched performance and reliability can be achieved.

Note: Alibaba Cloud SLB is the overarching service, with ALB, NLB, and CLB as specialized subtypes.

Disclaimer: The views expressed herein are for reference only and don't necessarily represent the official views of Alibaba Cloud.

Networking Server Load Balancer Load Balancing Application Load Balancer Classic Load Balancer Network Load Balancer
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