Load balancing in Azure

Load balancers manage how network traffic is distributed across an application. Load balancers are essential in keeping your application resilient to individual component failures and to ensure your application is available to process requests. For applications that don’t have service discovery built in, load balancing is required for both availability sets and availability zones.

Azure possesses three load balancing technology services that are distinct in their abilities to route network traffic:

  • Azure Traffic Manager provides global DNS load balancing. You would consider using Traffic Manager to provide load balancing of DNS endpoints within or across Azure regions. Traffic manager will distribute requests to available endpoints, and use endpoint monitoring to detect and remove failed endpoints from load.
  • Azure Application Gateway provides Layer 7 load-balancing capabilities, such as round-robin distribution of incoming traffic, cookie-based session affinity, URL path-based routing, and the ability to host multiple websites behind a single application gateway. Application Gateway by default monitors the health of all resources in its back-end pool and automatically removes any resource considered unhealthy from the pool. Application Gateway continues to monitor the unhealthy instances and adds them back to the healthy back-end pool once they become available and respond to health probes.
  • Azure Load Balancer is a layer 4 load balancer. You can configure public and internal load-balanced endpoints and define rules to map inbound connections to back-end pool destinations by using TCP and HTTP health-probing options to manage service availability.

One or a combination of all three Azure load-balancing technologies can ensure you have the necessary options available to architect a highly available solution to route network traffic through your application.

Azure load balancing optionsAn illustration showing the different load balancing technology in Azure. The traffic manager balances the load between two regions. Within each region there is an application gateway that distributes the load among different virtual machines in the web tier based on the type of request. All images requests go to the image server pool, and any other request is directed to the default server pool. Further requests coming from the default server pools are handled by the Azure load balancer to distribute them among the virtual machines in the database tier.

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