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AWS Load Balancer AZ Check

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AWS Load Balancer AZ Check is a built-in Command Probe template that validates the availability of one or more target availability zones in a given Application Load Balancer (ALB) or Classic Load Balancer (CLB) during a chaos experiment. Use it to assert that load balancer zone coverage and multi-AZ redundancy hold up while a fault disrupts a zone or the network path to it.

The probe runs the healthchecks utility bundled in the chaos probe image, queries the Elastic Load Balancing API, and prints [Pass] when the target zones are available on the load balancer. The comparator marks the probe as passed when the output contains [Pass].

Built-in probe template

This is a built-in Command Probe template that runs on Kubernetes chaos infrastructure. Add it to an experiment from the probe library and customize its inputs. Go to Built-in probe templates to browse the full library, or go to Command probe to understand how command probes work.

Use cases​

Use this probe template to:

  • Verify load balancer availability zone configuration during AZ failures.
  • Validate traffic distribution across availability zones.
  • Monitor load balancer health during network chaos experiments.
  • Confirm that multi-AZ redundancy is maintained.

How the probe works​

The template configures a Command Probe that runs healthchecks -name aws-lb-az. The utility resolves the load balancer from LOAD_BALANCER_ARN (for an ALB) or LOAD_BALANCER_NAME (for a CLB) in the supplied REGION, calls the Elastic Load Balancing API, and prints [Pass] when every zone in ZONES is available on the load balancer. The comparator passes the probe when the output contains [Pass], and fails it otherwise.

Prerequisites​

  • Chaos infrastructure: A Kubernetes chaos infrastructure with network access to the Elastic Load Balancing API endpoints.
  • AWS credentials: Cloud credentials available to the chaos infrastructure, with the permissions listed below.
  • Target load balancer exists: The ALB referenced by LOAD_BALANCER_ARN or the CLB referenced by LOAD_BALANCER_NAME exists in REGION.

Permissions required​

The credentials used by the probe need the following AWS actions:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "elasticloadbalancing:DescribeLoadBalancers"
      ],
      "Resource": "*"
    }
  ]
}

The probe uses the AWS credentials available to your chaos infrastructure. Go to AWS IAM integration to set up access through IAM Roles for Service Accounts (IRSA), or go to common policy for all AWS faults to apply a single superset policy.

Probe properties​

Command​

healthchecks -name aws-lb-az

Comparator​

TypeCriteriaValue
stringcontains[Pass]

The probe passes when the command output contains [Pass], which indicates that the target availability zones are configured on the load balancer.

Environment variables​

VariableDescriptionRequiredDefault
LOAD_BALANCER_ARNARN of the ALB to check (for example, arn:aws:elasticloadbalancing:us-east-1:123456789012:loadbalancer/app/my-alb/1234567890abcdef). Provide this for an ALB.Conditional-
LOAD_BALANCER_NAMEName of the CLB to check (for example, my-classic-lb). Provide this for a CLB.Conditional-
REGIONAWS region where the load balancer is located (for example, us-east-1, eu-west-2).Yes-
ZONESComma-separated list of availability zones to check (for example, us-east-1a,us-east-1b,us-east-1c).Yes-
Load balancer selection

Provide LOAD_BALANCER_ARN for an Application Load Balancer or LOAD_BALANCER_NAME for a Classic Load Balancer.

Run properties​

PropertyDescriptionTypeDefault
timeoutMaximum time to wait for the probe to complete (for example, 30s, 1m, 5m).String300s
intervalTime between probe executions (for example, 5s, 30s, 1m).String10s
attemptNumber of retry attempts before the probe is marked as failed.Integer1
pollingIntervalTime between retry attempts (for example, 1s, 5s, 10s).String-
initialDelayInitial delay before the probe starts (for example, 0s, 10s, 30s).String-
stopOnFailureStop the experiment if the probe fails.Booleanfalse
verbosityLog verbosity level (info, debug, trace).String-

Troubleshooting​

AWS Load Balancer AZ Check probe fails with an authorization error

The credentials available to the chaos infrastructure do not have the required Elastic Load Balancing permissions in the target region. Confirm that the IAM policy attached to the role or IRSA service account includes elasticloadbalancing:DescribeLoadBalancers, and that any policy condition allows the region passed in REGION.

AWS Load Balancer AZ Check probe cannot find the load balancer

The load balancer did not resolve in the supplied REGION. For an ALB, confirm that LOAD_BALANCER_ARN is correct and that you did not also set LOAD_BALANCER_NAME. For a CLB, confirm that LOAD_BALANCER_NAME is correct. Verify that REGION matches the load balancer region.

AWS Load Balancer AZ Check probe reports a zone is unavailable

One or more zones listed in ZONES are not enabled on the load balancer, or were removed by the injected fault. Confirm that the values in ZONES exactly match the availability zones attached to the load balancer, and that the experiment is expected to keep those zones enabled at the probe's execution phase.