Global server load balancing (GSLB) is an important component of internet infrastructure that supports business operations online. Traditionally, apps in multiple datacenters would use a simple domain name system (DNS) to look up locations. This would involve a list of IP addresses and a simple round-robin distribution of traffic across datacenter locations.
However, there are factors that can affect app performance like network latency, which is an essential metric when it comes to measuring quality of service (QoS). That’s why leveraging advanced algorithms for GSLB is important to delivering fast app responses and a great user experience.
In this blog series, we will look at how Citrix App Delivery and Security (CADS) service provides a fully managed, SaaS-based cloud load balancing solution for three different use cases. We will also discuss CADS service functionality that can contribute to improved QoS.
How Advanced GSLB Supports App Availability
GSLB is generally used to enable:
- Disaster recovery
- Improved application performance
- Greater reliability
- Fulfilment of compliance requirements
- Efficient connections
- Reduced latency
In typical configurations, app data is served from one location (active), where most users access the resources, and one or more standby locations (passive) that serve as a backup if the active site fails. The switch from active to passive is called failover.
Another configuration type is an active-active deployment, where multiple sites are active at the same time. This requires a more advanced GSLB implementation, including constant monitoring of the health and latency of the sites from the end user’s location. These data can help admins provide optimal site performance and make decisions based on factors such as a user’s ISP-to-public-cloud-server-link performance, real-user performance monitoring data, and more.
CADS service advanced GSLB capabilities
CADS service leverages real-user performance monitoring data functionality and can perform data-driven DNS or API-based global load balancing. It employs end-user-based probes for collecting real-time information from clients, along with synthetic monitoring from multiple PoP locations globally, as shown in Figure 1. Based on the type of configuration specified in CADS service, users receive the optimal site information for their DNS queries. These sites can be on-prem, public, or in a private cloud.
CADS service offers a simplified workflow so admins can quickly deploy GSLB service to support globally distributed app sites. The graphic below shows the onboarding steps to get started with CADS service’s GSLB capabilities. Check out our product documentation for detailed deployment guidance.
Let’s look at an example use case where CADS service can support your GSLB needs so you can deliver a great experience to your users.
Disaster Recovery Site for On-Prem Datacenter in the Cloud – Active-Passive Mode
Use Case: Create a disaster recovery site in a public cloud for your existing on-prem datacenter.
In this case, you’re creating a multi-site app with CADS service in GSLB active-passive mode. Please note, detailed guidance is available in our product documentation, and the following steps are specific to this use case.
Specify Main and Backup Site
Add two sites (existing on-prem datacenter and a new public-cloud datacenter) for active-passive deployment, as shown in Figure 2.
Specify GSLB Parameters
Select Failover as the algorithm (Figure 3). By default, a priority of 1 is assigned to the primary site (Site1) and an increasing priority of 2 to the standby site (Site2), as shown in Figure 4.
Please note, CADS service does not manage the app data replication and sync between the primary and backup sites.
If a site with priority 1 is down, client requests are directed to the site with priority 2. If both sites are up, traffic is directed to Site1 because it has higher priority, as shown in Figure 5.
In our next blog post, we’ll cover even distribution of users across datacenters with persistence and optimal site selection with advanced GSLB capabilities.
Learn More
Learn more about Citrix App Delivery and Security service today, and try it by logging into your cloud.citrix.com account and clicking Request Trial on the App Delivery and Security tile.
