diff --git a/doc/Pacemaker_Explained/en-US/Ch-Advanced-Options.txt b/doc/Pacemaker_Explained/en-US/Ch-Advanced-Options.txt index fa039cf0f1..56847977d3 100644 --- a/doc/Pacemaker_Explained/en-US/Ch-Advanced-Options.txt +++ b/doc/Pacemaker_Explained/en-US/Ch-Advanced-Options.txt @@ -1,889 +1,820 @@ = Advanced Configuration = [[s-remote-connection]] == Connecting from a Remote Machine == indexterm:[Cluster,Remote connection] indexterm:[Cluster,Remote administration] Provided Pacemaker is installed on a machine, it is possible to connect to the cluster even if the machine itself is not in the same cluster. To do this, one simply sets up a number of environment variables and runs the same commands as when working on a cluster node. .Environment Variables Used to Connect to Remote Instances of the CIB [width="95%",cols="1m,1,3<",options="header",align="center"] |========================================================= |Environment Variable |Default |Description |CIB_user |$USER |The user to connect as. Needs to be part of the +haclient+ group on the target host. indexterm:[Environment Variable,CIB_user] |CIB_passwd | |The user's password. Read from the command line if unset. indexterm:[Environment Variable,CIB_passwd] |CIB_server |localhost |The host to contact indexterm:[Environment Variable,CIB_server] |CIB_port | |The port on which to contact the server; required. indexterm:[Environment Variable,CIB_port] |CIB_encrypted |TRUE |Whether to encrypt network traffic indexterm:[Environment Variable,CIB_encrypted] |========================================================= So, if *c001n01* is an active cluster node and is listening on port 1234 for connections, and *someuser* is a member of the *haclient* group, then the following would prompt for *someuser*'s password and return the cluster's current configuration: ---- # export CIB_port=1234; export CIB_server=c001n01; export CIB_user=someuser; # cibadmin -Q ---- For security reasons, the cluster does not listen for remote connections by default. If you wish to allow remote access, you need to set the +remote-tls-port+ (encrypted) or +remote-clear-port+ (unencrypted) CIB properties (i.e., those kept in the +cib+ tag, like +num_updates+ and +epoch+). .Extra top-level CIB properties for remote access [width="95%",cols="1m,1,3<",options="header",align="center"] |========================================================= |Field |Default |Description |remote-tls-port |_none_ |Listen for encrypted remote connections on this port. indexterm:[remote-tls-port,Remote Connection Option] indexterm:[Remote Connection,Option,remote-tls-port] |remote-clear-port |_none_ |Listen for plaintext remote connections on this port. indexterm:[remote-clear-port,Remote Connection Option] indexterm:[Remote Connection,Option,remote-clear-port] |========================================================= [[s-recurring-start]] == Specifying When Recurring Actions are Performed == By default, recurring actions are scheduled relative to when the resource started. So if your resource was last started at 14:32 and you have a backup set to be performed every 24 hours, then the backup will always run in the middle of the business day -- hardly desirable. To specify a date and time that the operation should be relative to, set the operation's +interval-origin+. The cluster uses this point to calculate the correct +start-delay+ such that the operation will occur at _origin + (interval * N)_. So, if the operation's interval is 24h, its interval-origin is set to 02:00 and it is currently 14:32, then the cluster would initiate the operation with a start delay of 11 hours and 28 minutes. If the resource is moved to another node before 2am, then the operation is cancelled. The value specified for +interval+ and +interval-origin+ can be any date/time conforming to the http://en.wikipedia.org/wiki/ISO_8601[ISO8601 standard]. By way of example, to specify an operation that would run on the first Monday of 2009 and every Monday after that, you would add: .Specifying a Base for Recurring Action Intervals ===== [source,XML] ===== [[s-failure-handling]] == Handling Resource Failure == By default, Pacemaker will attempt to recover failed resources by restarting them. However, failure recovery is highly configurable. === Failure Counts === Pacemaker tracks resource failures for each combination of node, resource, and operation (start, stop, monitor, etc.). You can query the fail count for a particular node, resource, and/or operation using the `crm_failcount` command. For example, to see how many times the 10-second monitor for +myrsc+ has failed on +node1+, run: ---- # crm_failcount --query -r myrsc -N node1 -n monitor -I 10s ---- If you omit the node, `crm_failcount` will use the local node. If you omit the operation and interval, `crm_failcount` will display the sum of the fail counts for all operations on the resource. You can use `crm_resource --cleanup` or `crm_failcount --delete` to clear fail counts. For example, to clear the above monitor failures, run: ---- # crm_resource --cleanup -r myrsc -N node1 -n monitor -I 10s ---- If you omit the resource, `crm_resource --cleanup` will clear failures for all resources. If you omit the node, it will clear failures on all nodes. If you omit the operation and interval, it will clear the failures for all operations on the resource. [NOTE] ==== Even when cleaning up only a single operation, all failed operations will disappear from the status display. This allows us to trigger a re-check of the resource's current status. ==== Higher-level tools may provide other commands for querying and clearing fail counts. The `crm_mon` tool shows the current cluster status, including any failed operations. To see the current fail counts for any failed resources, call `crm_mon` with the `--failcounts` option. This shows the fail counts per resource (that is, the sum of any operation fail counts for the resource). === Failure Response === Normally, if a running resource fails, pacemaker will try to stop it and start it again. Pacemaker will choose the best location to start it each time, which may be the same node that it failed on. However, if a resource fails repeatedly, it is possible that there is an underlying problem on that node, and you might desire trying a different node in such a case. Pacemaker allows you to set your preference via the +migration-threshold+ resource meta-attribute. footnote:[ The naming of this option was perhaps unfortunate as it is easily confused with live migration, the process of moving a resource from one node to another without stopping it. Xen virtual guests are the most common example of resources that can be migrated in this manner. ] If you define +migration-threshold=pass:[N]+ for a resource, it will be banned from the original node after 'N' failures. [NOTE] ==== The +migration-threshold+ is per 'resource', even though fail counts are tracked per 'operation'. The operation fail counts are added together to compare against the +migration-threshold+. ==== By default, fail counts remain until manually cleared by an administrator using `crm_resource --cleanup` or `crm_failcount --delete` (hopefully after first fixing the failure's cause). It is possible to have fail counts expire automatically by setting the +failure-timeout+ resource meta-attribute. [IMPORTANT] ==== A successful operation does not clear past failures. If a recurring monitor operation fails once, succeeds many times, then fails again days later, its fail count is 2. Fail counts are cleared only by manual intervention or falure timeout. ==== For example, a setting of +migration-threshold=2+ and +failure-timeout=60s+ would cause the resource to move to a new node after 2 failures, and allow it to move back (depending on stickiness and constraint scores) after one minute. [NOTE] ==== +failure-timeout+ is measured since the most recent failure. That is, older failures do not individually time out and lower the fail count. Instead, all failures are timed out simultaneously (and the fail count is reset to 0) if there is no new failure for the timeout period. ==== There are two exceptions to the migration threshold concept: when a resource either fails to start or fails to stop. If the cluster property +start-failure-is-fatal+ is set to +true+ (which is the default), start failures cause the fail count to be set to +INFINITY+ and thus always cause the resource to move immediately. Stop failures are slightly different and crucial. If a resource fails to stop and STONITH is enabled, then the cluster will fence the node in order to be able to start the resource elsewhere. If STONITH is not enabled, then the cluster has no way to continue and will not try to start the resource elsewhere, but will try to stop it again after the failure timeout. [IMPORTANT] Please read <> to understand how timeouts work before configuring a +failure-timeout+. == Moving Resources == indexterm:[Moving,Resources] indexterm:[Resource,Moving] === Moving Resources Manually === There are primarily two occasions when you would want to move a resource from its current location: when the whole node is under maintenance, and when a single resource needs to be moved. ==== Standby Mode ==== Since everything eventually comes down to a score, you could create constraints for every resource to prevent them from running on one node. While pacemaker configuration can seem convoluted at times, not even we would require this of administrators. Instead, one can set a special node attribute which tells the cluster "don't let anything run here". There is even a helpful tool to help query and set it, called `crm_standby`. To check the standby status of the current machine, run: ---- # crm_standby -G ---- A value of +on+ indicates that the node is _not_ able to host any resources, while a value of +off+ says that it _can_. You can also check the status of other nodes in the cluster by specifying the `--node` option: ---- # crm_standby -G --node sles-2 ---- To change the current node's standby status, use `-v` instead of `-G`: ---- # crm_standby -v on ---- Again, you can change another host's value by supplying a hostname with `--node`. ==== Moving One Resource ==== When only one resource is required to move, we could do this by creating location constraints. However, once again we provide a user-friendly shortcut as part of the `crm_resource` command, which creates and modifies the extra constraints for you. If +Email+ were running on +sles-1+ and you wanted it moved to a specific location, the command would look something like: ---- # crm_resource -M -r Email -H sles-2 ---- Behind the scenes, the tool will create the following location constraint: [source,XML] It is important to note that subsequent invocations of `crm_resource -M` are not cumulative. So, if you ran these commands ---- # crm_resource -M -r Email -H sles-2 # crm_resource -M -r Email -H sles-3 ---- then it is as if you had never performed the first command. To allow the resource to move back again, use: ---- # crm_resource -U -r Email ---- Note the use of the word _allow_. The resource can move back to its original location but, depending on +resource-stickiness+, it might stay where it is. To be absolutely certain that it moves back to +sles-1+, move it there before issuing the call to `crm_resource -U`: ---- # crm_resource -M -r Email -H sles-1 # crm_resource -U -r Email ---- Alternatively, if you only care that the resource should be moved from its current location, try: ---- # crm_resource -B -r Email ---- Which will instead create a negative constraint, like [source,XML] This will achieve the desired effect, but will also have long-term consequences. As the tool will warn you, the creation of a +-INFINITY+ constraint will prevent the resource from running on that node until `crm_resource -U` is used. This includes the situation where every other cluster node is no longer available! In some cases, such as when +resource-stickiness+ is set to +INFINITY+, it is possible that you will end up with the problem described in <>. The tool can detect some of these cases and deals with them by creating both positive and negative constraints. E.g. +Email+ prefers +sles-1+ with a score of +-INFINITY+ +Email+ prefers +sles-2+ with a score of +INFINITY+ which has the same long-term consequences as discussed earlier. === Moving Resources Due to Connectivity Changes === You can configure the cluster to move resources when external connectivity is lost in two steps. ==== Tell Pacemaker to Monitor Connectivity ==== First, add an *ocf:pacemaker:ping* resource to the cluster. The *ping* resource uses the system utility of the same name to a test whether list of machines (specified by DNS hostname or IPv4/IPv6 address) are reachable and uses the results to maintain a node attribute called +pingd+ by default. footnote:[ The attribute name is customizable, in order to allow multiple ping groups to be defined. ] [NOTE] =========== Older versions of Heartbeat required users to add ping nodes to +ha.cf+, but this is no longer required. Older versions of Pacemaker used a different agent *ocf:pacemaker:pingd* which is now deprecated in favor of *ping*. If your version of Pacemaker does not contain the *ping* resource agent, download the latest version from https://github.com/ClusterLabs/pacemaker/tree/master/extra/resources/ping =========== Normally, the ping resource should run on all cluster nodes, which means that you'll need to create a clone. A template for this can be found below along with a description of the most interesting parameters. .Common Options for a 'ping' Resource [width="95%",cols="1m,4<",options="header",align="center"] |========================================================= |Field |Description |dampen |The time to wait (dampening) for further changes to occur. Use this to prevent a resource from bouncing around the cluster when cluster nodes notice the loss of connectivity at slightly different times. indexterm:[dampen,Ping Resource Option] indexterm:[Ping Resource,Option,dampen] |multiplier |The number of connected ping nodes gets multiplied by this value to get a score. Useful when there are multiple ping nodes configured. indexterm:[multiplier,Ping Resource Option] indexterm:[Ping Resource,Option,multiplier] |host_list |The machines to contact in order to determine the current connectivity status. Allowed values include resolvable DNS host names, IPv4 and IPv6 addresses. indexterm:[host_list,Ping Resource Option] indexterm:[Ping Resource,Option,host_list] |========================================================= .An example ping cluster resource that checks node connectivity once every minute ===== [source,XML] ------------ ------------ ===== [IMPORTANT] =========== You're only half done. The next section deals with telling Pacemaker how to deal with the connectivity status that +ocf:pacemaker:ping+ is recording. =========== ==== Tell Pacemaker How to Interpret the Connectivity Data ==== [IMPORTANT] ====== Before attempting the following, make sure you understand <>. ====== There are a number of ways to use the connectivity data. The most common setup is for people to have a single ping target (e.g. the service network's default gateway), to prevent the cluster from running a resource on any unconnected node. .Don't run a resource on unconnected nodes ===== [source,XML] ------- ------- ===== A more complex setup is to have a number of ping targets configured. You can require the cluster to only run resources on nodes that can connect to all (or a minimum subset) of them. .Run only on nodes connected to three or more ping targets. ===== [source,XML] ------- ... ... ... ------- ===== Alternatively, you can tell the cluster only to _prefer_ nodes with the best connectivity. Just be sure to set +multiplier+ to a value higher than that of +resource-stickiness+ (and don't set either of them to +INFINITY+). .Prefer the node with the most connected ping nodes ===== [source,XML] ------- ------- ===== It is perhaps easier to think of this in terms of the simple constraints that the cluster translates it into. For example, if *sles-1* is connected to all five ping nodes but *sles-2* is only connected to two, then it would be as if you instead had the following constraints in your configuration: .How the cluster translates the above location constraint ===== [source,XML] ------- ------- ===== The advantage is that you don't have to manually update any constraints whenever your network connectivity changes. You can also combine the concepts above into something even more complex. The example below shows how you can prefer the node with the most connected ping nodes provided they have connectivity to at least three (again assuming that +multiplier+ is set to 1000). .A more complex example of choosing a location based on connectivity ===== [source,XML] ------- ------- ===== [[s-migrating-resources]] === Migrating Resources === Normally, when the cluster needs to move a resource, it fully restarts the resource (i.e. stops the resource on the current node and starts it on the new node). However, some types of resources, such as Xen virtual guests, are able to move to another location without loss of state (often referred to as live migration or hot migration). In pacemaker, this is called resource migration. Pacemaker can be configured to migrate a resource when moving it, rather than restarting it. Not all resources are able to migrate; see the Migration Checklist below, and those that can, won't do so in all situations. Conceptually, there are two requirements from which the other prerequisites follow: * The resource must be active and healthy at the old location; and * everything required for the resource to run must be available on both the old and new locations. The cluster is able to accommodate both 'push' and 'pull' migration models by requiring the resource agent to support two special actions: +migrate_to+ (performed on the current location) and +migrate_from+ (performed on the destination). In push migration, the process on the current location transfers the resource to the new location where is it later activated. In this scenario, most of the work would be done in the +migrate_to+ action and, if anything, the activation would occur during +migrate_from+. Conversely for pull, the +migrate_to+ action is practically empty and +migrate_from+ does most of the work, extracting the relevant resource state from the old location and activating it. There is no wrong or right way for a resource agent to implement migration, as long as it works. .Migration Checklist * The resource may not be a clone. * The resource must use an OCF style agent. * The resource must not be in a failed or degraded state. * The resource agent must support +migrate_to+ and +migrate_from+ actions, and advertise them in its metadata. * The resource must have the +allow-migrate+ meta-attribute set to +true+ (which is not the default). If an otherwise migratable resource depends on another resource via an ordering constraint, there are special situations in which it will be restarted rather than migrated. For example, if the resource depends on a clone, and at the time the resource needs to be moved, the clone has instances that are stopping and instances that are starting, then the resource will be restarted. The Policy Engine is not yet able to model this situation correctly and so takes the safer (if less optimal) path. In pacemaker 1.1.11 and earlier, a migratable resource will be restarted when moving if it directly or indirectly depends on 'any' primitive or group resources. Even in newer versions, if a migratable resource depends on a non-migratable resource, and both need to be moved, the migratable resource will be restarted. [[s-node-health]] == Tracking Node Health == A node may be functioning adequately as far as cluster membership is concerned, and yet be "unhealthy" in some respect that makes it an undesirable location for resources. For example, a disk drive may be reporting SMART errors, or the CPU may be highly loaded. Pacemaker offers a way to automatically move resources off unhealthy nodes. === Node Health Attributes === Pacemaker will treat any node attribute whose name starts with +#health+ as an indicator of node health. Node health attributes may have one of the following values: .Allowed Values for Node Health Attributes [width="95%",cols="1,3<",options="header",align="center"] |========================================================= |Value |Intended significance |+red+ |This indicator is unhealthy indexterm:[Node health,red] |+yellow+ |This indicator is becoming unhealthy indexterm:[Node health,yellow] |+green+ |This indicator is healthy indexterm:[Node health,green] |'integer' |A numeric score to apply to all resources on this node (0 or positive is healthy, negative is unhealthy) indexterm:[Node health,score] |========================================================= === Node Health Strategy === Pacemaker assigns a node health score to each node, as the sum of the values of all its node health attributes. This score will be used as a location constraint applied to this node for all resources. The +node-health-strategy+ cluster option controls how Pacemaker responds to changes in node health attributes, and how it translates +red+, +yellow+, and +green+ to scores. Allowed values are: .Node Health Strategies [width="95%",cols="1m,3<",options="header",align="center"] |========================================================= |Value |Effect |none |Do not track node health attributes at all. indexterm:[Node health,none] |migrate-on-red |Assign the value of +-INFINITY+ to +red+, and 0 to +yellow+ and +green+. This will cause all resources to move off the node if any attribute is +red+. indexterm:[Node health,migrate-on-red] |only-green |Assign the value of +-INFINITY+ to +red+ and +yellow+, and 0 to +green+. This will cause all resources to move off the node if any attribute is +red+ or +yellow+. indexterm:[Node health,only-green] |progressive |Assign the value of the +node-health-red+ cluster option to +red+, the value of +node-health-yellow+ to +yellow+, and the value of +node-health-green+ to +green+. Each node is additionally assigned a score of +node-health-base+ (this allows resources to start even if some attributes are +yellow+). This strategy gives the administrator finer control over how important each value is. indexterm:[Node health,progressive] |custom |Track node health attributes using the same values as +progressive+ for +red+, +yellow+, and +green+, but do not take them into account. The administrator is expected to implement a policy by defining rules (see <>) referencing node health attributes. indexterm:[Node health,custom] |========================================================= === Measuring Node Health === Since Pacemaker calculates node health based on node attributes, any method that sets node attributes may be used to measure node health. The most common ways are resource agents or separate daemons. Pacemaker provides examples that can be used directly or as a basis for custom code. The +ocf:pacemaker:HealthCPU+ and +ocf:pacemaker:HealthSMART+ resource agents set node health attributes based on CPU and disk parameters. The +ipmiservicelogd+ daemon sets node health attributes based on IPMI values (the +ocf:pacemaker:SystemHealth+ resource agent can be used to manage the daemon as a cluster resource). -[[s-reusing-config-elements]] -== Reusing Rules, Options and Sets of Operations == - -Sometimes a number of constraints need to use the same set of rules, -and resources need to set the same options and parameters. To -simplify this situation, you can refer to an existing object using an -+id-ref+ instead of an id. - -So if for one resource you have - -[source,XML] ------- - - - - - ------- - -Then instead of duplicating the rule for all your other resources, you can instead specify: - -.Referencing rules from other constraints -===== -[source,XML] -------- - - - -------- -===== - -[IMPORTANT] -=========== -The cluster will insist that the +rule+ exists somewhere. Attempting -to add a reference to a non-existing rule will cause a validation -failure, as will attempting to remove a +rule+ that is referenced -elsewhere. -=========== - -The same principle applies for +meta_attributes+ and -+instance_attributes+ as illustrated in the example below: - -.Referencing attributes, options, and operations from other resources -===== -[source,XML] -------- - - - - - - - - - - - - - - - - - - - - -------- -===== - == Reloading Services After a Definition Change == The cluster automatically detects changes to the definition of services it manages. The normal response is to stop the service (using the old definition) and start it again (with the new definition). This works well, but some services are smarter and can be told to use a new set of options without restarting. To take advantage of this capability, the resource agent must: . Accept the +reload+ operation and perform any required actions. _The actions here depend completely on your application!_ + .The DRBD agent's logic for supporting +reload+ ===== [source,Bash] ------- case $1 in start) drbd_start ;; stop) drbd_stop ;; reload) drbd_reload ;; monitor) drbd_monitor ;; *) drbd_usage exit $OCF_ERR_UNIMPLEMENTED ;; esac exit $? ------- ===== . Advertise the +reload+ operation in the +actions+ section of its metadata + .The DRBD Agent Advertising Support for the +reload+ Operation ===== [source,XML] ------- 1.1 Master/Slave OCF Resource Agent for DRBD ... ------- ===== . Advertise one or more parameters that can take effect using +reload+. + Any parameter with the +unique+ set to 0 is eligible to be used in this way. + .Parameter that can be changed using reload ===== [source,XML] ------- Full path to the drbd.conf file. Path to drbd.conf ------- ===== Once these requirements are satisfied, the cluster will automatically know to reload the resource (instead of restarting) when a non-unique field changes. [NOTE] ====== Metadata will not be re-read unless the resource needs to be started. This may mean that the resource will be restarted the first time, even though you changed a parameter with +unique=0+. ====== [NOTE] ====== If both a unique and non-unique field are changed simultaneously, the resource will still be restarted. ====== diff --git a/doc/Pacemaker_Explained/en-US/Ch-Reusing-Configuration.txt b/doc/Pacemaker_Explained/en-US/Ch-Reusing-Configuration.txt index 1324c25d10..aaccbca406 100644 --- a/doc/Pacemaker_Explained/en-US/Ch-Reusing-Configuration.txt +++ b/doc/Pacemaker_Explained/en-US/Ch-Reusing-Configuration.txt @@ -1,238 +1,307 @@ = Reusing Parts of the Configuration = Pacemaker provides multiple ways to simplify the configuration XML by reusing parts of it in multiple places. Besides simplifying the XML, this also allows you to manipulate multiple configuration elements with a single reference. == Reusing Resource Definitions == If you want to create lots of resources with similar configurations, defining a 'resource template' simplifies the task. Once defined, it can be referenced in primitives or in certain types of constraints. === Configuring Resources with Templates === The primitives referencing the template will inherit all meta-attributes, instance attributes, utilization attributes and operations defined in the template. And you can define specific attributes and operations for any of the primitives. If any of these are defined in both the template and the primitive, the values defined in the primitive will take precedence over the ones defined in the template. Hence, resource templates help to reduce the amount of configuration work. If any changes are needed, they can be done to the template definition and will take effect globally in all resource definitions referencing that template. Resource templates have a syntax similar to that of primitives. .Resource template for a migratable Xen virtual machine ==== [source,XML] ---- ---- ==== Once you define a resource template, you can use it in primitives by specifying the +template+ property. .Xen primitive resource using a resource template ==== [source,XML] ---- ---- ==== In the example above, the new primitive +vm1+ will inherit everything from +vm-template+. For example, the equivalent of the above two examples would be: .Equivalent Xen primitive resource not using a resource template ==== [source,XML] ---- ---- ==== If you want to overwrite some attributes or operations, add them to the particular primitive's definition. .Xen resource overriding template values ==== [source,XML] ---- ---- ==== In the example above, the new primitive +vm2+ has special attribute values. Its +monitor+ operation has a longer +timeout+ and +interval+, and the primitive has an additional +stop+ operation. To see the resulting definition of a resource, run: ---- # crm_resource --query-xml --resource vm2 ---- To see the raw definition of a resource in the CIB, run: ---- # crm_resource --query-xml-raw --resource vm2 ---- === Using Templates in Constraints === A resource template can be referenced in the following types of constraints: - +order+ constraints (see <>) - +colocation+ constraints (see <>) - +rsc_ticket+ constraints (for multi-site clusters as described in <>) Resource templates referenced in constraints stand for all primitives which are derived from that template. This means, the constraint applies to all primitive resources referencing the resource template. Referencing resource templates in constraints is an alternative to resource sets and can simplify the cluster configuration considerably. For example, given the example templates earlier in this chapter: [source,XML] would colocate all VMs with +base-rsc+ and is the equivalent of the following constraint configuration: [source,XML] ---- ---- [NOTE] ====== In a colocation constraint, only one template may be referenced from either `rsc` or `with-rsc`; the other reference must be a regular resource. ====== === Using Templates in Resource Sets === Resource templates can also be referenced in resource sets. For example, given the example templates earlier in this section, then: [source,XML] ---- ---- is the equivalent of the following constraint using a sequential resource set: [source,XML] ---- ---- Or, if the resources referencing the template can run in parallel, then: [source,XML] ---- ---- is the equivalent of the following constraint configuration: [source,XML] ---- ---- + +[[s-reusing-config-elements]] +== Reusing Rules, Options and Sets of Operations == + +Sometimes a number of constraints need to use the same set of rules, +and resources need to set the same options and parameters. To +simplify this situation, you can refer to an existing object using an ++id-ref+ instead of an +id+. + +So if for one resource you have + +[source,XML] +------ + + + + + +------ + +Then instead of duplicating the rule for all your other resources, you can instead specify: + +.Referencing rules from other constraints +===== +[source,XML] +------- + + + +------- +===== + +[IMPORTANT] +=========== +The cluster will insist that the +rule+ exists somewhere. Attempting +to add a reference to a non-existing rule will cause a validation +failure, as will attempting to remove a +rule+ that is referenced +elsewhere. +=========== + +The same principle applies for +meta_attributes+ and ++instance_attributes+ as illustrated in the example below: + +.Referencing attributes, options, and operations from other resources +===== +[source,XML] +------- + + + + + + + + + + + + + + + + + + + + +------- +=====