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[Figure] Dependency relationship
In MCCS, you can configure the dependency relationship of resources by using a tree.
From the above screen, we can find out about the dependency relationship among resources.
The network address resource as a parent depends on the NIC resource as its child. The application resource as a parent depends on the network address resource as its child.
MCCS performs a failover on a group basis. Thus, all the resources within a group should be connected in this dependency relationship and they need to be put into a single group before we can provide meaningful service.
If we set two resources as a parent and an child, we can see it as two vertical levels. The max level can be checked in the 'MaxDependencyLevel' value in the group attribute menu.
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Link
[Figure] Setting Link
The The above screen shows how to set the link between the process resource (parent) and the network address resource (child).
The network address resource (child) depends on the process resource (parent).
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Basic Dependency Cases among resources
Following are the general cases of dependency.
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Network Interface card(NIC) Resource, Network Address Resource
Before assigning an IP address to the network address resource, you need to first have a physical network card. Without a network card, you cannot assign an IP address. If you set the NIC resource as an child and the network address resource as a parent, it will check whether the network card is normal when the network address resources tries to go online.
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Disk Resource, Network Address Resource, Application Resource (ex: DB)
Many applications record data in a disk or storage. Thus, applications must depend on disks in the dependency relationship.
If you use the DB, you need to designate the disk to record data in. Thus, for the DB, you must set the dependency relationship where the DB as a parent depends on the disk as a child.
If a client needs an IP address to access the DB, you must set the network address as an child and the DB as a parent. Based on this dependency relationship, when a group goes online in MCCS, first check the network address resource and confirm whether the disk are unlocked properly before running the DB.
Thus the DB should be set to depend on both the network address resource and the disk resource.
We can provide the following configurations based on the dependency relationships discussed so far.
[Figure] Dependency of database application
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- On the assumption that the value of RestartLimit is 1 for resource r2, the first failure has occurred.
- MCCS will bring online resource r2 again as the value of RestartLimit.
At this time, resource r1 which depends on resource r2 will be taken offline. - resource r2 restart.
- resource r1 online.
- When another failure occurs on resource r2, all of the resource will be taken offline from resource r1 to r3 by order.
- Resource r3 will be taken offline.
- As a result, resource r2 is considered as failure and all resources in the group is offline status in the node.