How GSLB Improves Reliability and Performance Across Multi-Cloud Environments

Today, users expect instant access and uninterrupted online service. The ability to deliver applications reliably and efficiently across geographical boundaries is a critical capability.

Global Server Load Balancing addresses this need by intelligently directing traffic, ensuring optimal user experience, maximizing application uptime, and providing robust protection against regional outages. It's an essential technology for any enterprise operating global web services or seeking to build resilient, high-performance digital infrastructure.

What is Global Server Load Balancing?

Global Server Load Balancing (GSLB) is an advanced method of distributing Internet and web application traffic across multiple servers located in different geographic regions. The primary goal of Global Server Load Balancing is to improve the performance of Web-based applications and servers.

GSLB also plays a crucial role in disaster recovery and business continuity by automatically redirecting traffic to backup sites if a server or data center fails, ensuring continuous service availability.

Essentially, GSLB provides load balancing for load balancers, optimizing performance across global servers and services in large, distributed enterprises.

How GSLB works

Instances of web applications and services may be cached on web servers and Content Delivery Networks (CDNs) around the world. GSLB evaluates various environmental parameters of the user's traffic, such as:

• Latency
• Server load
• User proximity
• Network bandwidth
• Service availability

At its core, GSLB operates by intelligently manipulating the Domain Name System (DNS) resolution process. When a user attempts to access a web application, their device first queries a DNS server to translate the human-readable domain name (e.g., example.com) into an IP address.

Instead of providing a static IP, a GSLB-enabled DNS server intercepts this request and, based on its evaluation of various parameters, responds with the IP address of the most suitable server or data center. This redirection happens seamlessly at the DNS level, before any actual application traffic is sent, ensuring the user's connection is established with the optimal resource from the outset.

GSLB optimizes traffic routing to an optimal site or data center, thereby preventing any single site from being overloaded. Local load balancers within the chosen site then distribute requests to individual web servers.

Relation to load balancers

The concept is similar to load balancers that distribute IT workloads across multiple servers within the same network environment. The goal of the load balancer is to:

1. Optimize the application performance for the end user.
2. Maximize resource utilization in a distributed cloud-based network environment.

Global Server Load Balancing scales the same concept to the globally distributed connected Internet. You can consider the GSLB to be a load balancer for load balancers in multicloud environments.

Characteristics of GSLB

A key aspect of GSLB is its operation primarily at the DNS layer (Layer 7 of the OSI model). This means GSLB makes its routing decisions by returning an optimal IP address in response to a DNS query, rather than directly inspecting or forwarding application-level traffic.

Consequently, GSLB is inherently stateless from the perspective of the initial connection, as it simply provides a destination IP address and then steps out of the data path for that specific connection.

GSLB modifies Domain Name System (DNS) responses based on real-time network environmental parameters to direct web traffic to an optimal server location. Load balancing policies may be employed, such as:

• Geolocation routing to the closest server location
• Latency-based routing for the fastest response
• Health-aware routing to utilize only healthy servers

If a server or an entire data center fails, GSLB updates the relevant DNS records to point to a healthy alternative. However, clients' DNS resolvers may cache the old records for a duration specified by the Time-To-Live (TTL), meaning traffic might continue to be directed to the failed IP until the cache expires.

GSLB uses dynamic policies and load balancing algorithms that modify DNS records to share web traffic and application workloads. In contrast, IP Anycast offers a different approach

IP Anycast: A contrasting approach

IP Anycast is a networking technique where multiple servers or network nodes, often located in different geographical regions, are configured to share and advertise the exact same IP address. When a user sends a request to this shared Anycast IP address, network routing protocols (like BGP) direct the request to the "closest" available server advertising that IP, based on network topology and path efficiency — not necessarily physical distance.

This approach offers several benefits, including reduced latency by connecting users to the nearest available resource, increased redundancy and high availability as traffic is automatically rerouted if a node fails, and improved DDoS mitigation by distributing attack traffic across multiple points.

GSLB vs. IP Anycast

While both GSLB and IP Anycast contribute to redundancy and performance, they operate at different layers and use distinct mechanisms for traffic distribution and failover

Load balancing algorithms

GSLB intelligently routes traffic across the Internet, operating primarily at the DNS level and utilizing algorithms designed to optimize network performance metrics such as latency, availability, capacity, and application performance. The following algorithms are commonly used for GSLB:

• Round Robin and Weighted Round Robin: A simple routing approach that cycles through the available entities in a predefined order. The path or importance of each entity may be assigned a weight, or the routing may follow a heuristic to determine the optimal network traffic route
• Latency-based routing: Network traffic is directed to servers exhibiting the lowest latency and fastest response time for specific users, based on their network parameters such as proximity, availability, and bandwidth
• Geo-based routing (GeoDNS) and Proximity-Based Routing: Traffic is routed based on the user's geographical location in relation to the network servers. This strategy is useful for compliance (data sovereignty), content localization, or regional performance.
• Health-based routing: Not all servers perform equally well under all conditions. Furthermore, some traffic requests may require higher standards of service availability and disaster recovery capabilities. A health or failover-based routing strategy directs network traffic to healthy network endpoints and servers, determined by continuous health checks.

Failover modes for GSLB

A variety of failover modes may be available for the Global Server Load Balancing system

An Active-Active configuration typically comprises multiple active network environments (such as multicloud, on-premises datacenters, and hybrid cloud systems). All server sites are active and connected to the GSLB-managed pool of sites.

In contrast, an Active-Passive GSLB configuration comprises an active and a passive server environment (or site). The active sites serve incoming traffic if they operate within defined health, capacity, and application performance standards. In the event of a performance failure, the passive sites are activated to prevent an outage from impacting the application performance and end-user experience.

Advanced GSLB features and integrations

Modern GSLB implementations use real-time network performance and user demand to determine an optimal path for load balancing and traffic distribution across globally dispersed data centers. These advanced GSLB solutions extend beyond basic traffic steering, offering advanced features and integrations.

In cloud environments, major providers offer their own GSLB-like services, such as AWS Route 53, Azure Traffic Manager, and Google Cloud DNS. These cloud-native solutions integrate seamlessly with their respective cloud ecosystems, providing similar global traffic management capabilities and often leveraging the provider's extensive global network infrastructure for optimized performance and resilience.

Advanced features often include:

• Deep analytics and reporting to visualize traffic patterns and performance
• API-driven management for automation and orchestration
• Enhanced security capabilities

GSLB can integrate with Web Application Firewalls (WAFs) and DDoS mitigation services to direct traffic away from compromised regions or filter malicious requests, contributing to a comprehensive security posture.

While GSLB primarily employs the above algorithms that focus on selecting the optimal site or data center for a user, it often integrates with local load balancers at each site that might use algorithms like Weighted Least Connections to optimize traffic distribution to individual servers within that site.

GSLB in hybrid and multi-cloud environments

GSLB plays a pivotal role in broader enterprise network strategies, particularly in hybrid and multi-cloud architectures. By intelligently distributing traffic across on-premises data centers and multiple public cloud providers, GSLB ensures business continuity and optimizes resource utilization in complex environments.

It complements technologies like SD-WAN by making intelligent routing decisions at the application entry point, helping to steer users to the best performing application instance regardless of where it resides, thereby enhancing the overall resilience and efficiency of a globally distributed infrastructure.

Managing GSLB and IP Anycast: Considerations

While major cloud providers offer integrated GSLB-like services, it’s common for enterprise organizations to manage their own GSLB and IP Anycast implementations, particularly if they:

• Do not rely solely on one provider.
• Have complex on-premises infrastructure.
• Require vendor-agnostic solutions.

For GSLB, this often involves deploying dedicated hardware or software appliances from specialized vendors, or utilizing advanced features offered by managed DNS providers. These solutions provide granular control over global traffic distribution policies, health checks, and algorithm selection.

For IP Anycast, management typically falls into two categories: organizations with their own Autonomous System (AS) can directly configure their network routers to advertise the same IP address from multiple locations using BGP. Alternatively, many leverage the extensive networks of CDNs or specialized DNS providers, which offer Anycast as part of their service, abstracting away the underlying BGP complexities.

For businesses operating digitally, GSLB is a strategic necessity that guarantees an optimal user experience, ensures continuous application availability, and builds resilience against outages across your distributed infrastructure. Leveraging robust networking solutions from Cisco, GSLB forms the backbone of global application delivery. With the comprehensive observability offered by the Splunk unified data platform, organizations gain invaluable insights into GSLB's performance and traffic dynamics, enabling proactive optimization and securing a competitive edge in a demanding marketplace.