Amazon ELB with cross-zone load balancing


When AWS announced cross-zone load balancing, it changed the way how Amazon ELB (Elastic Load Balancing) used to route incoming requests. This made it the deployment process of applications across multiple Availability Zones (AZs) way easier than before.

Enabling cross-zone load balancing in Amazon ELB

Amazon ELB performs operations such as detection of unhealthy EC2 instances, spreading instances across healthy channels, etc.

In cross-zone load balancing, the nodes for your load balancer distribute requests from clients to the registered targets. When cross-zone load balancing is enabled, each load balancer node distributes traffic across the registered targets in all enabled availability zones. When cross-zone load balancing is disabled, each load balancer node distributes traffic across the registered targets in its Availability Zone only.

It is important that Cross-zone load balancing should be enabled as it reduces the uneven distribution of traffic when clients have an unequal number of instances in each Availability Zone (AZ).

Know whether you have cross-zone load balancing enabled

Centilytics has a dedicated insight which shows the status regarding cross-zone load balancing and gives warnings to the user whenever a load balancer with disabled cross-zone load balancing is detected.

Insight descriptions:

There can be 1 possible scenario:

Severity Description
Warning This indication will be displayed when your Elastic load balancer does not have cross-zone load balancing enabled.


Description of further columns are as follows:

  1. Account Id: This column shows the respective account ID of the user’s account.AWS ELB 1
  2. Account Name: This column shows the Account Id of the user’s account.AWS ELB 5
  3. Region: This column shows the region in which the resources exist.AWS ELB 7
  4. Identifier: This column shows the name of the load balancer.AWS ELB 3

Filters applicable:

Filter Name Description
Account Id Applying the account Id filter will display data for the selected account Id.
Region Applying the region filter will display data according to the selected region.
Severity Applying severity filter will display data according to the selected severity type i.e. selecting critical will display all resources with critical severity. Same will be the case for Warning and OK severity types
Resource Tags Applying resource tags filter will display those resources which have been assigned the selected resource tag. For e.g., A user has tagged some public snapshots by a resource tag named environment. Then selecting an environment from the resource tags filter will display all those resources tagged by the tag name environment.
Resource Tags Value Applying resource tags value filter will display data which will have the selected resource tag value. For e.g. – Let’s say a user has tagged some resource by a tag named environment and has a value say production (environment: production).

Hence, the user can view data of all the resources which have “environment:production” tag assigned. The user can use the tag value filter only when a tag name has been provided.


Compliances covered:

Compliance Name Reference No. Link
Trusted Advisor



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