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49 lines
2.4 KiB
ReStructuredText
49 lines
2.4 KiB
ReStructuredText
Introduction
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============
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When dealing with large clusters, it is desirable to have more than one node,
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the xCAT Management Node (MN), handle the installation and management of the
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Com[pute Nodes (CN). The concept of these additional "helper" nodes are called
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**Service Nodes (SN)**. The Management Node can delegate all management
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operations required by a compute node to the service node that is assigned to
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manage that Compute Node. You can configure one or more Service Nodes to install
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and manage a group of Compute Nodes.
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Service Nodes
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-------------
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With xCAT, you have the choice of either having each Service Node
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install/manage a specific set of compute nodes, or having a pool of Service
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Nodes, any of which can respond to an installation request from a compute
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node. (Service Node pools must be aligned with the network broadcast domains,
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because the way a compute node choose its Service Node for that boot is by whoever
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responds to the DHCP request broadcast first.) You can also have a hybrid of
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the 2 approaches, in which for each specific set of compute nodes you have 2
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or more Service Nodes in a pool.
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Each Service Node runs an instance of xcatd, just like the Management Node does.
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The ``xcatd`` daemons communicate with each other using the same XML/SSH protocol
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that the xCAT clients use to communicate with ``xcatd`` on the Management Node.
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Daemon-based Databases
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----------------------
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The Service Nodes will need to communicate with the xCAT database on the Management
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Node and do this by using the remote client capabilities of the database. Therefore,
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the Management Node must be running one of the daemon-based databases supported by
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xCAT (PostgreSQL, MySQL, MariaDB, etc).
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The default SQLite database does not support remote clients and cannot be used
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in hierarchical clusters. This document includes instructions for migrating
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your cluster from SQLite to one of the other databases. Since the initial
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install of xCAT will always set up SQLite, you must migrate to a database that
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supports remote clients before installing your Service Nodes.
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Setup
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-----
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xCAT will help you install your Service Nodes as well as install on the xCAT-SN
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software and other required rpms and pre-reqs. Service Nodes require the same
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software as installed on the Management Node with the exception of the top level
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xCAT rpm. The Management Node installs the ``xCAT`` package while the Service Nodes
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install the ``xCATsn`` package.
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