e84da9e7b6
Editing the nested sections for the compute chapter. Mostly grammar,
wording, style, convention, etc. This patch includes service groups,
image management, building blocks, management tools, and nova networking.
Watch this space for more.
Partial-Bug: #1251195
Change-Id: I07c021b653787dd95ffeba70e67f9b66f6eb242c
114 lines
6.3 KiB
XML
114 lines
6.3 KiB
XML
<!DOCTYPE section [
|
|
<!ENTITY % openstack SYSTEM "../../common/entities/openstack.ent">
|
|
%openstack;
|
|
]><section xmlns="http://docbook.org/ns/docbook"
|
|
xmlns:xi="http://www.w3.org/2001/XInclude"
|
|
xmlns:xlink="http://www.w3.org/1999/xlink"
|
|
version="5.0"
|
|
xml:id="configuring-compute-service-groups">
|
|
<title>Configure Compute service groups</title>
|
|
<para>The Compute service must know the status of each compute node to
|
|
effectively manage and use them. This can include events like a user
|
|
launching a new VM, the scheduler sending a request to a live node, or a
|
|
query to the ServiceGroup API to determine if a node is live.</para>
|
|
<para>When a compute worker running the
|
|
<systemitem class="service">nova-compute</systemitem> daemon starts, it
|
|
calls the <systemitem>join</systemitem> API to join the compute group. Any
|
|
service (such as the scheduler) can query the group's membership and the
|
|
status of its nodes. Internally, the <systemitem>ServiceGroup</systemitem>
|
|
client driver automatically updates the compute worker status.</para>
|
|
|
|
<!-- I don't understand what "available" means in this context. Can someone please help? LKB
|
|
<para>The database, ZooKeeper, and Memcache drivers are available.</para>-->
|
|
|
|
<section xml:id="database-servicegroup-driver">
|
|
<title>Database ServiceGroup driver</title>
|
|
<para>By default, Compute uses the database driver to track if a node is
|
|
live. In a compute worker, this driver periodically sends a
|
|
<command>db update</command> command to the database, saying <quote>I'm
|
|
OK</quote> with a timestamp. Compute uses a pre-defined timeout
|
|
(<literal>service_down_time</literal>) to determine if a node is dead.</para>
|
|
<para>The driver has limitations, which can be problematic depending on
|
|
your environment. If a lot of compute worker nodes need to be checked,
|
|
the database can be put under heavy load, which can cause the timeout to
|
|
trigger, and a live node could incorrectly be considered dead. By default,
|
|
the timeout is 60 seconds. Reducing the timeout value can help in this
|
|
situation, but you must also make the database update more frequently,
|
|
which again increases the database workload.</para>
|
|
<para>The database contains data that is both transient (such as whether
|
|
the node is alive) and persistent (such as entries for VM owners). With
|
|
the ServiceGroup abstraction, Compute can treat each type separately.</para>
|
|
</section>
|
|
<section xml:id="zookeeper-servicegroup-driver">
|
|
<title>ZooKeeper ServiceGroup driver</title>
|
|
|
|
<para>The ZooKeeper ServiceGroup driver works by using ZooKeeper ephemeral
|
|
nodes. ZooKeeper, unlike databases, is a distributed system, with its
|
|
load divided among several servers. On a compute worker node, the driver
|
|
can establish a ZooKeeper session, then create an ephemeral znode
|
|
in the group directory. Ephemeral znodes have the same lifespan as the
|
|
session. If the worker node or the
|
|
<systemitem class="service">nova-compute</systemitem> daemon crashes, or
|
|
a network partition is in place between the worker and the ZooKeeper
|
|
server quorums, the ephemeral znodes are removed automatically. The
|
|
driver can be given group membership by running the <command>ls</command>
|
|
command in the group directory.</para>
|
|
<para>The ZooKeeper driver requires the ZooKeeper servers and client
|
|
libraries. Setting up ZooKeeper servers is outside the scope of this
|
|
guide (for more information, see
|
|
<link xlink:href="http://zookeeper.apache.org/">Apache Zookeeper</link>).
|
|
These client-side Python libraries must be installed on every nova node:</para>
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term><literal>python-zookeeper</literal></term>
|
|
<listitem><para>The official Zookeeper Python binding</para></listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><literal>evzookeeper</literal></term>
|
|
<listitem><para>This library makes the binding work with the eventlet
|
|
threading model.</para></listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
<para>This example assumes the ZooKeeper server addresses and ports are
|
|
<literal>192.168.2.1:2181</literal>, <literal>192.168.2.2:2181</literal>,
|
|
and <literal>192.168.2.3:2181</literal>.</para>
|
|
<para>These values in the <filename>/etc/nova/nova.conf</filename> file are
|
|
required on every node for the ZooKeeper driver:</para>
|
|
<programlisting language="ini"># Driver for the ServiceGroup service
|
|
servicegroup_driver="zk"
|
|
|
|
[zookeeper]
|
|
address="192.168.2.1:2181,192.168.2.2:2181,192.168.2.3:2181"</programlisting>
|
|
<para>To customize the Compute Service groups, use these configuration
|
|
option settings:</para>
|
|
<xi:include href="../../common/tables/nova-zookeeper.xml"/>
|
|
</section>
|
|
<section xml:id="memcache-servicegroup-driver">
|
|
<title>Memcache ServiceGroup driver</title>
|
|
<para>The <systemitem>memcache</systemitem> ServiceGroup driver uses
|
|
<systemitem>memcached</systemitem>, a distributed memory object
|
|
caching system that is used to increase site performance. For more
|
|
details, see <link xlink:href="http://memcached.org/">memcached.org</link>.</para>
|
|
<para>To use the <systemitem>memcache</systemitem> driver, you must
|
|
install <systemitem>memcached</systemitem>. You might already have
|
|
it installed, as the same driver is also used for the OpenStack
|
|
Object Storage and OpenStack dashboard. If you need to install
|
|
<systemitem>memcached</systemitem>, see the instructions in the <link
|
|
xlink:href="http://docs.openstack.org/"><citetitle>OpenStack
|
|
Installation Guide</citetitle></link>.</para>
|
|
<para>These values in the <filename>/etc/nova/nova.conf</filename> file
|
|
are required on every node for the <systemitem>memcache</systemitem>
|
|
driver:</para>
|
|
<programlisting language="ini"># Driver for the ServiceGroup service
|
|
servicegroup_driver="mc"
|
|
|
|
# Memcached servers. Use either a list of memcached servers to use for caching (list value),
|
|
# or "<None>" for in-process caching (default).
|
|
memcached_servers=<None>
|
|
|
|
# Timeout; maximum time since last check-in for up service (integer value).
|
|
# Helps to define whether a node is dead
|
|
service_down_time=60</programlisting>
|
|
</section>
|
|
</section>
|