en-US/health-checks-for-lb-rules.xml

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<section id="health-checks-for-lb-rules">
  <!-- CLOUDSTACK-443 -->
  <title>Health Checks for Load Balancer Rules</title>
  <para>(NetScaler load balancer only; requires NetScaler version 10.0)
  </para>
  <para>Health checks are used in load-balanced applications to ensure that requests are forwarded
    only to running, available services.
    When creating a load balancer rule, you can specify a health check policy.
    This is in addition to specifying the
    stickiness policy, algorithm, and other load balancer rule options.
    You can configure one health check policy per load balancer rule.</para>
  <para>Any load balancer rule defined on a NetScaler load balancer in &PRODUCT; can have a health check policy.
    The policy consists of a ping path, thresholds to define "healthy" and "unhealthy" states,
    health check frequency, and timeout wait interval.</para>
  <para>When a health check policy is in effect,
    the load balancer will stop forwarding requests to any resources that are found to be unhealthy.
    If the resource later becomes available again, the periodic health check
    will discover it, and the resource will once again be added to the pool of resources that can
    receive requests from the load balancer.
    At any given time, the most recent result of the health check is displayed in the UI.
    For any VM that is attached to a load balancer rule with a health check configured,
    the state will be shown as UP or DOWN in the UI depending on the result of the most recent health check.</para>
  <para>You can delete or modify existing health check policies.</para>
  <para>To configure how often the health check is performed by default, use the global
    configuration setting healthcheck.update.interval (default value is 600 seconds).
    You can override this value for an individual health check policy.</para>
  <para>For details on how to set a health check policy using the UI, see <xref linkend="add-load-balancer-rule"/>.</para>
</section>