ctdb/web/configuring.html

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   3
   4 <H2 align="center">Configuring CTDB</H2>
   5
   6 <h2>Clustering Model</h2>
   7
   8 The setup instructions on this page are modelled on setting up a cluster of N
   9 nodes that function in nearly all respects as a single multi-homed node.
  10 So the cluster will export N IP interfaces, each of which is equivalent
  11 (same shares) and which offers coherent CIFS file access across all
  12 nodes.<p>
  13
  14 The clustering model utilizes IP takeover techniques to ensure that
  15 the full set of public IP addresses assigned to services on the
  16 cluster will always be available to the clients even when some nodes
  17 have failed and become unavailable.
  18
  19 <h2>CTDB Cluster Configuration</h2>
  20
  21 These are the primary configuration files for CTDB.<p>
  22
  23 When CTDB is installed, it will install template versions of these
  24 files which you need to edit to suit your system.
  25
  26 <h3>/etc/sysconfig/ctdb</h3>
  27
  28 This file contains the startup parameters for ctdb.<p>
  29
  30 When you installed ctdb, a template config file should have been
  31 installed in /etc/sysconfig/ctdb.<p>
  32
  33 Edit this file, following the instructions in the template.<p>
  34
  35 The most important options are:
  36 <ul>
  37 <li>CTDB_NODES
  38 <li>CTDB_RECOVERY_LOCK
  39 <li>CTDB_PUBLIC_ADDRESSES
  40 </ul>
  41
  42 Please verify these parameters carefully.
  43
  44 <h4>CTDB_RECOVERY_LOCK</h4>
  45
  46 This parameter specifies the lock file that the CTDB daemons use to arbitrate
  47 which node is acting as a recovery master.<br>
  48
  49 This file MUST be held on shared storage so that all CTDB daemons in the cluster will access/lock the same file.<br><br>
  50
  51 You <strong>must</strong> specify this parameter.<br>
  52 There is no default for this parameter.
  53
  54 <h3>CTDB_NODES</h3>
  55
  56 This file needs to be created and should contain a list of the private
  57 IP addresses that the CTDB daemons will use in your cluster. One IP
  58 address for each node in the cluster.<p>
  59
  60 This should be a private non-routable subnet which is only used for
  61 internal cluster traffic. This file must be the same on all nodes in
  62 the cluster.<p>
  63
  64 Make sure that these IP addresses are automatically started when the
  65 cluster node boots and that each node can ping each other node.<p>
  66
  67 Example 4 node cluster:
  68 <pre>
  69   CTDB_NODES=/etc/ctdb/nodes
  70 </pre>
  71 Content of /etc/ctdb/nodes:
  72 <pre>
  73  10.1.1.1
  74  10.1.1.2
  75  10.1.1.3
  76  10.1.1.4
  77 </pre>
  78
  79 The default for this file is /etc/ctdb/nodes.
  80
  81
  82 <h3>CTDB_PUBLIC_ADDRESSES</h3>
  83
  84 Each node in a CTDB cluster contains a list of public addresses which that
  85 particular node can host.<p>
  86
  87 While running the CTDB cluster will assign each public address that exists in the entire cluster to one node that will host that public address.<p>
  88
  89 These are the addresses that the SMBD daemons and other services will
  90 bind to and which clients will use to connect to the cluster.<p>
  91
  92 <h3>Example 4 node cluster:</h3>
  93 <pre>
  94   CTDB_PUBLIC_ADDRESSES=/etc/ctdb/public_addresses
  95 </pre>
  96 Content of /etc/ctdb/public_addresses:
  97 <pre>
  98  192.168.1.1/24 eth0
  99  192.168.1.2/24 eth0
 100  192.168.2.1/24 eth1
 101  192.168.2.2/24 eth1
 102 </pre>
 103
 104 These are the IP addresses that you should configure in DNS for the
 105 name of the clustered samba server and are the addresses that CIFS
 106 clients will connect to.<p>
 107
 108 Configure it as one DNS A record (==name) with multiple IP addresses
 109 and let round-robin DNS distribute the clients across the nodes of the
 110 cluster.<p>
 111
 112 The CTDB cluster utilizes IP takeover techniques to ensure that as long as at least one node in the cluster is available, all the public IP addresses will always be available to clients.<p>
 113
 114 This means that if one physical node fails, the public addresses that
 115 node was serving will be taken over by a different node in the cluster. This
 116 provides a guarantee that all ip addresses exposed to clients will
 117 always be reachable by clients as long as at least one node still remains available in the cluster with the capability to host that public address (i.e. the public address exists in that nodes public_addresses file).
 118
 119 Do not assign these addresses to any of the interfaces on the
 120 host. CTDB will add and remove these addresses automatically at
 121 runtime.<p>
 122
 123 This parameter is used when CTDB operated in takeover ip mode.<p>
 124
 125 The usual location for this file is /etc/ctdb/public_addresses.<p><p>
 126
 127 <h3>Example 2:</h3>
 128 By using different public_addresses files on different nodes it is possible to
 129 partition the cluster into subsets of nodes.
 130
 131 <pre>
 132 Node 0 : /etc/ctdb/public_addresses
 133 10.1.1.1/24 eth0
 134 10.1.2.1/24 eth1
 135 </pre>
 136
 137 <pre>
 138 Node 1 : /etc/ctdb/public_addresses
 139 10.1.2.1/24 eth1
 140 10.1.3.1/24 eth2
 141 </pre>
 142
 143 <pre>
 144 Node 2 : /etc/ctdb/public_addresses
 145 10.1.3.2/24 eth2
 146 </pre>
 147
 148 In this example we have three nodes but a total of 4 public addresses.<p>
 149
 150 10.1.2.1 can be hosted by either node 0 or node 1 and will be available to clients as long as at least one of these nodes are available. Only if both nodes 0 and 1 fails will this public address become unavailable to clients.<p>
 151
 152 All other public addresses can only be served by one single node respectively and will therefore only be avialable if the respective node is also available.
 153
 154
 155 <h2>Event scripts</h2>
 156
 157 CTDB comes with a number of application specific event scripts that
 158 are used to do service specific tasks when the cluster has been
 159 reconfigured. These scripts are stored in /etc/ctdb/events.d/<p>
 160
 161 You do not need to modify these scripts if you just want to use
 162 clustered Samba or NFS but they serve as examples in case you want to
 163 add clustering support for other application servers we do not yet
 164 proivide event scripts for.<p>
 165
 166 Please see the service scripts that installed by ctdb in
 167 /etc/ctdb/events.d for examples of how to configure other services to
 168 be aware of the HA features of CTDB.<p>
 169
 170 Also see /etc/ctdb/events.d/README for additional documentation on how to
 171 create and manage event scripts.
 172
 173 <h2>TCP port to use for CTDB</h2>
 174
 175 CTDB defaults to use TCP port 4379 for its traffic.<p>
 176
 177 Configuring a different port to use for CTDB traffic is done by adding
 178 a ctdb entry to the /etc/services file.<p>
 179
 180 Example: for change CTDB to use port 9999 add the following line to /etc/services
 181 <pre>
 182  ctdb  9999/tcp
 183 </pre>
 184
 185 Note: all nodes in the cluster MUST use the same port or else CTDB
 186 will not start correctly.
 187
 188 <h2>Name resolution</h2>
 189
 190 You need to setup some method for your Windows and NFS clients to find
 191 the nodes of the cluster, and automatically balance the load between
 192 the nodes.<p>
 193
 194 We recommend that you use public ip addresses using
 195 CTDB_PUBLIC_INTERFACE/CTDB_PUBLIC_ADDRESSES and that you setup a
 196 round-robin DNS entry for your cluster, listing all the public IP
 197 addresses that CTDB will be managing as a single DNS A record.<p>
 198
 199 You may also wish to setup a static WINS server entry listing all of
 200 your cluster nodes IP addresses.
 201
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