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Add hierarchy documents including introduction, database management,defining node, service node setup, test service node and appendix. TODO: resolve the fake_todo link reference in the following patch
51 lines
2.4 KiB
ReStructuredText
51 lines
2.4 KiB
ReStructuredText
Introduction
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============
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In large clusters, it is desirable to have more than one node (the Management
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Node - MN) handle the installation and management of the compute nodes. We
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call these additional nodes **service nodes (SN)**. The management node can
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delegate all management operations needed by a compute node to the SN that is
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managing that compute node. You can have one or more service nodes setting up
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to install and manage groups 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 SN 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 SNs in a pool.
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Each SN runs an instance of xcatd, just like the MN does. The xcatd daemons
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communicate with each other using the same XML/SSL protocol that the xCAT
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client uses to communicate with xcatd on the MN.
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Daemon-based Databases
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----------------------
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The service nodes need to communicate with the xCAT database on the Management
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Node. They do this by using the remote client capability of the database (i.e.
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they don't go through xcatd for that). Therefore the Management Node must be
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running one of the daemon-based databases supported by xCAT (PostgreSQL,
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MySQL).
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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 SNs
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xCAT software and other required rpms such as perl, the database client, and
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other pre-reqs. Service nodes require all the same software as the MN
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(because it can do all of the same functions), except that there is a special
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top level xCAT rpm for SNs called xCATsn vs. the xCAT rpm that is on the
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Management Node. The xCATsn rpm tells the SN that the xcatd on it should
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behave as an SN, not the MN.
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