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CLOUDSTACK-867. DOC. Incorporate reviewer comments on dynamic CPU and RAM scaling for running VMs.
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-->
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<section id="best-practices-vm">
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<title>Best Practices for Virtual Machines</title>
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<para>The &PRODUCT; administrator should monitor the total number of VM instances in each
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cluster, and disable allocation to the cluster if the total is approaching the maximum that
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the hypervisor can handle. Be sure to leave a safety margin to allow for the possibility of
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one or more hosts failing, which would increase the VM load on the other hosts as the VMs
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are automatically redeployed. Consult the documentation for your chosen hypervisor to find
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the maximum permitted number of VMs per host, then use &PRODUCT; global configuration
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settings to set this as the default limit. Monitor the VM activity in each cluster at all
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times. Keep the total number of VMs below a safe level that allows for the occasional host
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failure. For example, if there are N hosts in the cluster, and you want to allow for one
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host in the cluster to be down at any given time, the total number of VM instances you can
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permit in the cluster is at most (N-1) * (per-host-limit). Once a cluster reaches this
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number of VMs, use the &PRODUCT; UI to disable allocation of more VMs to the
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cluster.</para>
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<title>Best Practices for Virtual Machines</title>
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<para>For VMs to work as expected and provide excellent service, follow these guidelines.</para>
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<section id="best-practices-vm-monitoring">
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<title>Monitor VMs for Max Capacity</title>
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<para>The &PRODUCT; administrator should monitor the total number of VM instances in each
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cluster, and disable allocation to the cluster if the total is approaching the maximum that
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the hypervisor can handle. Be sure to leave a safety margin to allow for the possibility of
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one or more hosts failing, which would increase the VM load on the other hosts as the VMs
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are automatically redeployed. Consult the documentation for your chosen hypervisor to find
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the maximum permitted number of VMs per host, then use &PRODUCT; global configuration
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settings to set this as the default limit. Monitor the VM activity in each cluster at all
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times. Keep the total number of VMs below a safe level that allows for the occasional host
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failure. For example, if there are N hosts in the cluster, and you want to allow for one
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host in the cluster to be down at any given time, the total number of VM instances you can
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permit in the cluster is at most (N-1) * (per-host-limit). Once a cluster reaches this
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number of VMs, use the &PRODUCT; UI to disable allocation of more VMs to the
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cluster.</para>
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</section>
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<section id="best-practices-vm-tools">
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<title>Install Required Tools and Drivers</title>
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<para>Be sure the following are installed on each VM:</para>
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<itemizedlist>
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<listitem><para>For XenServer, install PV drivers and Xen tools on each VM.
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This will enable live migration and clean guest shutdown.
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Xen tools are required in order for dynamic CPU and RAM scaling to work.</para></listitem>
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<listitem><para>For vSphere, install VMware Tools on each VM.
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This will enable console view to work properly.
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VMware Tools are required in order for dynamic CPU and RAM scaling to work.</para></listitem>
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</itemizedlist>
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<para>To be sure that Xen tools or VMware Tools is installed, use one of the following techniques:</para>
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<itemizedlist>
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<listitem><para>Create each VM from a template that already has the tools installed; or,</para></listitem>
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<listitem><para>When registering a new template, the administrator or user can indicate whether tools are
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installed on the template. This can be done through the UI
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or using the updateTemplate API; or,</para></listitem>
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<listitem><para>If a user deploys a virtual machine with a template that does not have
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Xen tools or VMware Tools, and later installs the tools on the VM,
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then the user can inform &PRODUCT; using the updateVirtualMachine API.
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After installing the tools and updating the virtual machine, stop
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and start the VM.</para></listitem>
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</itemizedlist>
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</section>
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</section>
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@ -23,13 +23,14 @@
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-->
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<section id="changing-service-offering-for-vm">
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<title>Changing the Service Offering for a VM</title>
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<para>To upgrade or downgrade the level of compute resources available to a virtual machine, you can change the VM's compute offering.</para>
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<orderedlist>
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<listitem><para>Log in to the &PRODUCT; UI as a user or admin.</para></listitem>
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<listitem><para>In the left navigation, click Instances.</para></listitem>
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<listitem><para>Choose the VM that you want to work with.</para></listitem>
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<listitem><para>(Skip this step if you have enabled dynamic VM scaling; see <xref linkend="change-cpu-ram-for-vm"/>.)</para>
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<para>Click the Stop button to stop the VM.<inlinemediaobject>
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<para>To upgrade or downgrade the level of compute resources available to a virtual machine, you can change the VM's compute offering.</para>
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<orderedlist>
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<listitem><para>Log in to the &PRODUCT; UI as a user or admin.</para></listitem>
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<listitem><para>In the left navigation, click Instances.</para></listitem>
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<listitem><para>Choose the VM that you want to work with.</para></listitem>
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<listitem><para>(Skip this step if you have enabled dynamic VM scaling; see <xref linkend="change-cpu-ram-for-vm"/>.)</para>
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<para>Click the Stop button to stop the VM.
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<inlinemediaobject>
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<imageobject>
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<imagedata fileref="./images/stop-instance-icon.png"/>
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</imageobject>
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@ -37,48 +38,71 @@
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<phrase>StopButton.png: button to stop a VM</phrase>
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</textobject>
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</inlinemediaobject>
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</para></listitem>
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<listitem><para>Click the Change Service button.<inlinemediaobject>
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<imageobject>
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<imagedata fileref="./images/change-service-icon.png"/>
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</imageobject>
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<textobject>
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<phrase>ChangeServiceButton.png: button to change the service of a
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VM</phrase>
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</textobject>
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</inlinemediaobject></para>
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<para>The Change service dialog box is displayed.</para></listitem>
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<listitem><para>Select the offering you want to apply to the selected VM.</para></listitem>
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<listitem><para>Click OK.</para></listitem>
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</orderedlist>
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</para></listitem>
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<listitem><para>Click the Change Service button.<inlinemediaobject>
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<imageobject>
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<imagedata fileref="./images/change-service-icon.png"/>
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</imageobject>
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<textobject>
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<phrase>ChangeServiceButton.png: button to change the service of a
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VM</phrase>
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</textobject>
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</inlinemediaobject></para>
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<para>The Change service dialog box is displayed.</para></listitem>
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<listitem><para>Select the offering you want to apply to the selected VM.</para></listitem>
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<listitem><para>Click OK.</para></listitem>
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</orderedlist>
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<section id="change-cpu-ram-for-vm">
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<!-- CLOUDSTACK-658 -->
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<!-- CS-17394 -->
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<title>CPU and Memory Scaling for Running VMs</title>
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<para>(Supported on VMware and XenServer)</para>
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<para>It is not always possible to accurately predict the CPU and RAM requirements
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when you first deploy a VM.
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You might need to increase or decrease these resources at any time during the life of a VM.
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You might need to increase these resources at any time during the life of a VM.
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You can dynamically modify CPU and RAM levels to
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change these resources for a running VM without incurring any downtime.</para>
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scale up these resources for a running VM without incurring any downtime.</para>
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<para>Dynamic CPU and RAM scaling can be used in the following cases:</para>
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<itemizedlist>
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<listitem><para>New VMs that are created
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after the installation of &PRODUCT; 4.2.
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If you are upgrading from a previous version of &PRODUCT;,
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your existing VMs created with previous versions
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will not have the dynamic scaling capability.</para>
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</listitem>
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<listitem><para>User VMs on hosts running VMware and XenServer.</para></listitem>
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<listitem><para>System VMs on VMware.</para></listitem>
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<listitem><para>VM Tools or XenServer Tools must be installed on the virtual machine.</para></listitem>
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<listitem><para>VMware Tools or XenServer Tools must be installed on the virtual machine.</para></listitem>
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<listitem><para>The new requested CPU and RAM values must be within the constraints allowed by the hypervisor
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and the VM operating system.</para></listitem>
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<listitem><para>New VMs that are created
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after the installation of &PRODUCT; 4.2
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can use the dynamic scaling feature.
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If you are upgrading from a previous version of &PRODUCT;,
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your existing VMs created with previous versions
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will not have the dynamic scaling capability
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unless you update them using the following procedure.</para>
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</listitem>
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</itemizedlist>
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</section>
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<section id="update-vms">
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<title>Updating Existing VMs</title>
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<para>If you are upgrading from a previous version of &PRODUCT;,
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and you want your existing VMs created with previous versions
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to have the dynamic scaling capability,
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update the VMs using the following steps:</para>
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<orderedlist>
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<listitem><para>Make sure the zone-level setting "dynamic scalable" is set to true.</para></listitem>
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<listitem><para>Install Xen tools (for XenServer hosts) or VMware Tools (for VMware hosts) on each VM
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if they are not already installed.</para></listitem>
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<listitem><para>Stop the VM.</para></listitem>
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<listitem><para>Click the isDynamic Scaling checkbox.</para></listitem>
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<listitem><para>Restart the VM.</para></listitem>
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</orderedlist>
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</section>
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<section id="configure-dynamic-scaling">
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<title>Configuring Dynamic CPU and RAM Scaling</title>
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<para>To configure this feature, use the following new global configuration variables:</para>
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<itemizedlist>
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<listitem><para>enable.dynamic.scale.vm: Set to True to enable the feature. By default, the feature is turned off.</para></listitem>
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<listitem><para>scale.retry: How many times to attempt the scaling operation. Default = 2.</para></listitem>
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</itemizedlist>
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</section>
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<section id="dynamic-scaling-howto">
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<title>How to Dynamically Scale CPU and RAM</title>
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<para>To modify the CPU and/or RAM capacity of a virtual machine,
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you need to change
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the compute offering of the VM to a new compute offering that has the
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If there is no host in the cluster that can fulfill the requested level of CPU and RAM,
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the scaling operation will fail.
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The VM will continue to run as it was before.</para>
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<warning><para>&PRODUCT; will not check to be sure that the new CPU and RAM levels are compatible
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with the OS running on the VM.</para></warning>
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</section>
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<section id="dynamic-scaling-limitations">
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<title>Limitations</title>
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<itemizedlist>
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<listitem><para>You can not do dynamic scaling for system VMs on XenServer.</para></listitem>
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<listitem><para>&PRODUCT; will not check to be sure that the new CPU and RAM levels are compatible
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with the OS running on the VM.</para></listitem>
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<listitem><para>When scaling memory or CPU for a Linux VM on VMware, you might
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need to run scripts in addition to the other steps mentioned above.
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For more information, see
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<ulink url="http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1012764">Hot adding memory in Linux (1012764)</ulink>
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in the VMware Knowledge Base.</para></listitem>
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<listitem><para>(VMware) If resources are not available on the current host,
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scaling up will fail on VMware because of a known issue where &PRODUCT; and vCenter calculate the available capacity differently.
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For more information, see
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<ulink url="https://issues.apache.org/jira/browse/CLOUDSTACK-1809">https://issues.apache.org/jira/browse/CLOUDSTACK-1809</ulink>.</para></listitem>
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<listitem><para>On VMs running Linux 64-bit and Windows 7 32-bit operating systems,
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if the VM is initially assigned a RAM of less than 3 GB,
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it can be dynamically scaled up to 3 GB, but not more.
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This is due to a known issue with these operating systems, which will freeze
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if an attempt is made to dynamically scale from less than 3 GB to more than 3 GB.
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</para></listitem>
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</itemizedlist>
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</section>
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</section>
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