About Load Balancing
  • 08 Feb 2024
  • 3 Minutes to read
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About Load Balancing

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Article Summary

Overview

Load balancing refers to distributing the incoming traffic dynamically across a group of backend servers. This balancing of the load is handled by “Load Balancers”.

A load balancer is a service or application that sits between the incoming client requests and the backend servers. It acts as a primary point of contact for all incoming requests as it is configured to receive requests from a single URL. This URL is publicly exposed and is secured via SSL.

Load balancers internally route data to each of the servers in a Cluster based on configured criteria. The following document discusses and explains common uses for a load balancer in Decisions-based server architecture.

Note:

All the configurations for load distribution must be done at the Load balancer. There are no configurations for load distribution at the Decisions server. For more information refer to Load Balancing.

When choosing a Load balancer, there are two key points to consider:

Cookie-Based Session Persistence

Session persistence, specifically cookie-based, ensures that a user's requests are consistently directed to the same backend server throughout their session. It associates a unique identifier (cookie) with a user, allowing the load balancer to maintain the user's session state.

Why do Decisions need Session Persistence?

Decisions use Cookie-Based Session Persistence to maintain data during user interactions. For instance, when a user fills out a Form, it ensures a stable connection to the server. Without it, the user might be directed to different servers, risking data loss in the Form. Session persistence achieves this by associating a unique session identifier (usually stored in a cookie) with the user. The load balancer uses this identifier to consistently route the user's requests to the same server, preserving their session state.

WebSocket Support

WebSocket is a two-way communication protocol that enables both the client and server to exchange messages in real-time, using a continuous connection. This is different from the conventional HTTP, where one end sends a request, and the other end responds. In contrast, WebSocket provides a more effective way of exchanging information instantly and continuously between client and server.

Why do Decisions need WebSockets?

WebSockets are used to maintain sticky sessions, allowing multiple events to be sent from the server to the client more quickly.

WebSocket URL: [PortalBaseURL]/events


The following table lists a few of the Load balancers that support Cookie-based session persistence and WebSocket.

Load balancer Name

Sticky Session Support

WebSocket Support

Azure Load balancer

AWS Elastic Load balancer

Azure Application Gateway

Google Cloud Load Balancing

NGINX

Citrix ADC

HAProxy

F5 BIG-IP Platform

Kemp LoadMaster


SSL (Secured Socket Layer) Termination at Load Balancer

SSL Termination or SSL Offloading is removing the SSL-based encryption from incoming traffic at the Load balancer and sending the decrypted request to the servers. This reduces the computational work of the servers to increase their efficiency.

While offloading SSL, the https to http redirection must be configured at Load Balancer and not on the Decisions server.

If SSL is Terminated at the Load Balancer

Users can install Decisions without adding any SSL certificate to the application server. This will allow the servers to receive requests only in http. Thus it is important to configure the following settings in settings.xml.

  • Ensure that the EnableHttp is set to true in Settings.xml.

  • When SSL is terminated the servers send requests in HTTP to the load balancer, but the load balancer (LB) is set up to accept only HTTPS, then ForceBaseURI helps to send specific data in HTTPS. Users must add the following setting in the Settings.xml.

<ForceBaseURI>LoadBalancerURL</ForceBaseURI>

Configuring Health Check

Load balancers monitor the status of application servers with a health probe. The health probe adds or removes servers/VMs from the load balancer based on their response to health checks. The app server Health Monitor, or HealthCheck, provides a summary of the overall health of the platform. For more information, refer to the article App Server Health Monitor.

HealthCheck URL: [PortalBaseURL]/home/healthcheck


For further information on Installation, visit the Decisions Forum.


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