mirror of https://github.com/apache/cloudstack.git
91 lines
5.3 KiB
XML
91 lines
5.3 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="elastic-ip">
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<title>About Elastic IP</title>
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<para>Elastic IP (EIP) addresses are the IP addresses that are associated with an account, and act
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as static IP addresses. The account owner has complete control over the Elastic IP addresses
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that belong to the account. You can allocate an Elastic IP to a VM of your choice from the EIP
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pool of your account. Later if required you can reassign the IP address to a different VM. This
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feature is extremely helpful during VM failure. Instead of replacing the VM which is down, the
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IP address can be reassigned to a new VM in your account. Elastic IP service provides Static NAT
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(1:1) service in an EIP-enabled basic zone. The default network offering,
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DefaultSharedNetscalerEIPandELBNetworkOffering, provides your network with EIP and ELB network
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services if a NetScaler device is deployed in your zone. Similar to the public IP address,
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Elastic IP addresses are also mapped to their associated private IP addresses by using Stactic
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NAT.</para>
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<para>The EIP work flow is as follows:</para>
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<itemizedlist>
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<listitem>
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<para>When a user VM is deployed, a public IP is automatically acquired from the pool of
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public IPs configured in the zone. This IP is owned by the VM's account.</para>
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</listitem>
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<listitem>
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<para>Each VM will have its own private IP. When the user VM starts, Static NAT is provisioned
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on the NetScaler device by using the Inbound Network Address Translation (INAT) and Reverse
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NAT (RNAT) rules between the public IP and the private IP.</para>
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<note>
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<para>Inbound NAT (INAT) is a type of NAT supported by NetScaler, in which the destination
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IP address is replaced in the packets from the public network, such as the Internet, with
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the private IP address of a VM in the private network. Reverse NAT (RNAT) is a type of NAT
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supported by NetScaler, in which the source IP address is replaced in the packets
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generated by a VM in the private network with the public IP address.</para>
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</note>
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<para/>
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</listitem>
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<listitem>
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<para>This default public IP will be released in two cases:</para>
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<itemizedlist>
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<listitem>
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<para>When the VM is stopped. When the VM starts, it again receives a new public IP, not
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necessarily the same one allocated initially, from the pool of Public IPs.</para>
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</listitem>
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<listitem>
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<para>The user acquires a public IP (Elastic IP). This public IP is associated with the
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account, but will not be mapped to any private IP. However, the user can enable Static
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NAT to associate this IP to the private IP of a VM in the account. The Static NAT rule
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for the public IP can be disabled at any time. When Static NAT is disabled, a new public
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IP is allocated from the pool, which is not necessarily be the same one allocated
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initially.</para>
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</listitem>
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</itemizedlist>
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</listitem>
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</itemizedlist>
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<para>However, for the deployments where public IPs are limited resources, you have the
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flexibility to choose not to allocate a public IP by default. You can use the Associate Public
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IP option to turn on or off the automatic public IP assignment in the EIP-enabled Basic zones.
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If you turn off the automatic public IP assignment while creating a network offering, only a
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private IP is assigned to a VM when the VM is deployed with that network offering. Later, the
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user can acquire an IP for the VM and enable static NAT.</para>
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<para condition="admin">For more information on the Associate Public IP option, see <xref
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linkend="creating-network-offerings"/>.</para>
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<para condition="install">For more information on the Associate Public IP option, see the
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Administration Guide.</para>
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<note>
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<para>The Associate Public IP feature is designed only for use with user VMs. The System VMs
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continue to get both public IP and private by default, irrespective of the network offering
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configuration.</para>
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</note>
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<para/>
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<para>New deployments which use the default shared network offering with EIP and ELB services to
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create a shared network in the Basic zone will continue allocating public IPs to each user
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VM.</para>
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</section>
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