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52 lines
2.9 KiB
XML
52 lines
2.9 KiB
XML
<?xml version='1.0' encoding='utf-8' ?>
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<!DOCTYPE section PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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<!ENTITY % BOOK_ENTITIES SYSTEM "cloudstack.ent">
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%BOOK_ENTITIES;
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]>
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<!-- Licensed to the Apache Software Foundation (ASF) under one
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or more contributor license agreements. See the NOTICE file
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distributed with this work for additional information
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regarding copyright ownership. The ASF licenses this file
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to you under the Apache License, Version 2.0 (the
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"License"); you may not use this file except in compliance
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with the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing,
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software distributed under the License is distributed on an
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"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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KIND, either express or implied. See the License for the
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specific language governing permissions and limitations
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under the License.
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-->
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<section id="health-checks-for-lb-rules">
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<!-- CLOUDSTACK-443 -->
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<title>Health Checks for Load Balancer Rules</title>
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<para>(NetScaler load balancer only; requires NetScaler version 10.0)
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</para>
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<para>Health checks are used in load-balanced applications to ensure that requests are forwarded
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only to running, available services.
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When creating a load balancer rule, you can specify a health check policy.
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This is in addition to specifying the
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stickiness policy, algorithm, and other load balancer rule options.
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You can configure one health check policy per load balancer rule.</para>
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<para>Any load balancer rule defined on a NetScaler load balancer in &PRODUCT; can have a health check policy.
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The policy consists of a ping path, thresholds to define "healthy" and "unhealthy" states,
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health check frequency, and timeout wait interval.</para>
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<para>When a health check policy is in effect,
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the load balancer will stop forwarding requests to any resources that are found to be unhealthy.
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If the resource later becomes available again, the periodic health check
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will discover it, and the resource will once again be added to the pool of resources that can
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receive requests from the load balancer.
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At any given time, the most recent result of the health check is displayed in the UI.
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For any VM that is attached to a load balancer rule with a health check configured,
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the state will be shown as UP or DOWN in the UI depending on the result of the most recent health check.</para>
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<para>You can delete or modify existing health check policies.</para>
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<para>To configure how often the health check is performed by default, use the global
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configuration setting healthcheck.update.interval (default value is 600 seconds).
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You can override this value for an individual health check policy.</para>
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<para>For details on how to set a health check policy using the UI, see <xref linkend="add-load-balancer-rule"/>.</para>
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</section>
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