Document async status retrieval in NVP plugin
Document the Nicira plugin's asynchronous state retrieval process and the configuration options that discipline it. Bug 1250082 Change-Id: I63909184ebeb1cf080869c921b4aad983304ac82
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Salvatore Orlando
annegentle
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@ -43,6 +43,13 @@
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</abstract>
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</abstract>
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<revhistory>
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<revhistory>
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<revision>
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<date>2013-11-12</date>
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<revdescription><itemizedlist>
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<listitem><para>Adds options for tuning operational status synchronization
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in the NVP plugin.</para></listitem>
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</itemizedlist></revdescription>
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</revision>
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<revision>
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<revision>
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<date>2013-10-17</date>
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<date>2013-10-17</date>
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<revdescription>
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<revdescription>
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@ -1717,6 +1717,117 @@
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--provider:physical_network <L3-Gateway-Service-UUID> -provider:segmentation_id <VLAN_ID></userinput></screen>
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--provider:physical_network <L3-Gateway-Service-UUID> -provider:segmentation_id <VLAN_ID></userinput></screen>
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</section>
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</section>
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<section xml:id="section_nicira_nvp_plugin_status_sync">
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<title>Operational status synchronization in the
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Nicira NVP plugin</title>
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<para>Starting with the Havana release, the Nicira NVP plugin
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provides an asynchronous mechanism for retrieving the
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operational status for neutron resources from the NVP
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backend; this applies to <emphasis>network</emphasis>,
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<emphasis>port</emphasis>, and <emphasis>router</emphasis> resources.</para>
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<para>The backend is polled periodically, and the status for every resource is
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retrieved; then the status in the Neutron database is updated only for the
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resources for which a status change occurred. As operational status is now
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retrieved asynchronously, performance for <literal>GET</literal> operations is
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consistently improved.</para>
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<para>Data to retrieve from the backend are divided in chunks in order to avoid
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expensive API requests; this is achieved leveraging NVP APIs response paging
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capabilities. The minimum chunk size can be specified using a configuration
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option; the actual chunk size is then determined dynamically according to:
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total number of resources to retrieve, interval between two synchronization task
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runs, minimum delay between two subsequent requests to the NVP backend.</para>
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<para>The operational status synchronization can be tuned or disabled using the
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configuration options reported in the following table; it is however worth
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noting that the default values will work fine in most cases.</para>
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<table rules="all">
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<caption>Configuration options for tuning operational status synchronization
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in the NVP plugin</caption>
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<col width="12%"/>
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<col width="8%"/>
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<col width="10%"/>
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<col width="20%"/>
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<col width="50%"/>
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<thead>
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<tr>
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<th>Option name</th>
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<th>Group</th>
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<th>Default value</th>
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<th>Type and constraints</th>
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<th>Notes</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td><literal>state_sync_interval</literal></td>
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<td><literal>nvp_sync</literal></td>
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<td>120 seconds</td>
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<td>Integer; no constraint.</td>
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<td>Interval in seconds between two run of the synchronization task.
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If the synchronization task takes more than
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<literal>state_sync_interval</literal> seconds to execute, a
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new instance of the task is started as soon as the other is
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completed. Setting the value for this option to 0 will disable
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the synchronization task.</td>
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</tr>
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<tr>
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<td><literal>max_random_sync_delay</literal></td>
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<td><literal>nvp_sync</literal></td>
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<td>0 seconds</td>
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<td>Integer. Must not exceed
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<literal>min_sync_req_delay</literal></td>
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<td>When different from zero, a random delay between 0 and
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<literal>max_random_sync_delay</literal> will be added
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before processing the next chunk.</td>
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</tr>
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<tr>
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<td><literal>min_sync_req_delay</literal></td>
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<td><literal>nvp_sync</literal></td>
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<td>10 seconds</td>
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<td>Integer. Must not exceed
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<literal>state_sync_interval</literal>.</td>
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<td>The value of this option can be tuned according to the observed
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load on the NVP controllers. Lower values will result in faster
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synchronization, but might increase the load on the controller
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cluster.</td>
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</tr>
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<tr>
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<td><literal>min_chunk_size</literal></td>
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<td><literal>nvp_sync</literal></td>
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<td>500 resources</td>
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<td>Integer; no constraint.</td>
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<td>Minimum number of resources to retrieve from the backend for
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each synchronization chunk. The expected number of
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synchronization chunks is given by the ratio between
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<literal>state_sync_interval</literal> and
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<literal>min_sync_req_delay</literal>. This size of a chunk
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might increase if the total number of resources is such that
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more than <literal>min_chunk_size</literal> resources must be
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fetched in one chunk with the current number of chunks.</td>
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</tr>
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<tr>
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<td><literal>always_read_status</literal></td>
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<td><literal>nvp_sync</literal></td>
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<td>False</td>
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<td>Boolean; no constraint.</td>
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<td>When this option is enabled, the operational status will always
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be retrieved from the NVP backend ad every
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<literal>GET</literal> request. In this case it is advisable
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to disable the synchronization task.</td>
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</tr>
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</tbody>
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</table>
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<para>When running multiple Neutron server instances, the status
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synchronization task should not run on every node; doing so will need to
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unnecessary traffic towards the NVP backend as well as unnecessary DB
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operations. The configuration option <literal>state_sync_interval</literal>
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should therefore be non-zero exclusively on a node designated for backend status
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synchronization.</para>
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<para>Explicitly specifying the <emphasis role="italic">status</emphasis> attribute
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in Neutron API requests (e.g.: <literal>GET
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/v2.0/networks/<net-id>?fields=status&fields=name</literal>) will
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always trigger an explicit query to the NVP backend, even when asynchronous
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state synchronization is enabled.</para>
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</section>
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</section>
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</section>
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<section xml:id="section_bigswitch_extensions">
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<section xml:id="section_bigswitch_extensions">
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@ -1827,3 +1938,4 @@ source=10.10.10.0/24,destination=10.20.20.20/24,action=deny</userinput></screen>
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</section>
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</section>
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<!---->
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