[Figure] Online/Offline Sequence of Dependent Resources When Starting or Terminating a Group

Dependency Configuration

To define this dependency among resources, configure this link in the ‘Resource Dependency’ view from detailed information panel of MCCS console.

[Figure] Dependency relationship

You can simply configure the dependency link of these resources in a tree form.You can see the dependency among resources intuitively from the view above.
The IP address resource as a parent depends on the NIC resource as its child. The application resource as a parent depends on the IP address resource as its child.
Therefore, some resources as like IP address of above example can be both child and parent relatively.
As described before, When a single resource is failed MCCS failover all of the resources in a group. 
Therefore, when these are linked to one another as dependency rule and tied up together as a group, they can provide proper application service.
When you configure parent-child dependency link between two resources, there are 2 levels and the maximum level can be checked on value of  'MaxDependencyLevel' of group attribute.

Link

[Figure] Setting Link

The above screen shows how to set the dependency link between the process resource (parent) and the IP address resource (child). The process resource (parent) depends on the IP address resource (parent).

1. In the Group tab of the configuration tree of MCCS console, select the "Group" –> the "Resource dependency" tab from detailed information panel.
2. On the right palette screen, select "Create Dependency".
3. Select the parent resource (e.g. App) first and then select the child resource (e.g. IP address), then dependency link will be set.

Unlink

[Figure] Setting Unlink

1. When you unlink the dependency, select "Select" icon from the "Palette".
2. Select a dependency link to delete.
3. On the selected link, right click with your mouse button and select the "Unlink" button from pop up menu and click the "OK" button.

Dependency Attribute

[Figure] Edit DependancyType

You can review and edit a dependency attribute when you select a dependency among resources.
There are "OnlineDependency" and "OfflineDependency" in the dependency attribute.
This is applied when you bring online and take offline a resource within "Restartlimit"(For more details about Restartlimit, Please refer to "Chapter 7. Resource" in this manual.)

Basic Dependency Cases among resources

Following are the general cases of dependency.

Network Interface card(NIC) Resource, IP address Resource

A NIC must be online first to assign an IP address. It is impossible to assign an IP address without a NIC.  Accordingly, these two resources are dependent on each other with the network interface card being the child and the IP being the parent. 

When dependency is configured between both resources, MCCS checks NIC resource is online state before it bring online an IP address resource.

Disk Resource, IP address Resource, Application Resource (ex: DB)

Most applications may stores their data on the disks(storage). Accordingly, applications are dependent on disks.

For an instance, database service like MS-SQL or Oracle is not running properly without disk which contains data records.   

Therefore, both resources are dependent on each other with the database service being the parent and the disk becoming the child resource.

If a client needs an IP address for accessing database, both resources are dependent on each other with the database service being the parent and the IP address being the child.

On the basis of the dependency rule, MCCS will  bring online the database service after checking whether the IP address and disk resources were brought online properly when the group is brought online.

Accordingly, database service must depend on both IP address and disk resources at the same time to provide proper service.

If dependency is configured according to the relationship explained above, following diagram can be obtained.

[Figure] Dependency of database application

[Figure] Resource State Information Charts

Action by dependency attribute

• OnlineDependency

[Figure] Example of bring online of resource r1

OnlineDependency attribute of D1 between r1 and r2 is STRONG, OnlineDependency attribute of D2 between r1 and r3 is WEAK. 

1. MCCS check the Online Dependency attribute linked to r1.
2. Child resources, r4 -> r2 -> r1, are brought online in order to hierarchy when initiate resource online of r1 due to attribute of D1 is STRONG.
   (r3 isn't brought online due to attribute of D2 is WEAK.)

• OfflineDependency
  

[Figure] Example of take offline of resource r4

D1의 OfflineDependency attribute of D1 between r2 and r4 is STRONG, OfflineDependency attribute of D2 between r3 and r4 is WEAK. 

1. MCCS checks OfflineDependency attribute linked to r4.
2. Parents resources, r1 -> r2 -> r4, are taken offline in order to hierarchy when initiate resource offline of r4 due to attribute of D1 is D1 STRONG.
   (r3 isn't taken offline due to attribute of D2 is WEAK.)

Resource Critical Attributes

• Failure occurs from a resource on which critical resource depend.
  
  

[Figure] Example of Failure Occur 1

1. As a failure is occurred at resource r2, resource r1 will be taken offline(Since resource r1 depends on resource r2 which is failed, resource r1 may cannot be online properly).
2. Since resource r2 has critical attribute, resource r3 and a4 will be taken offline in order to failover the group.
3. As a result, resource r2 is considered as failure and all resources in the group will be taken offline

• Non-critical Resources
  
  

[Figure] Example of Failure Occur 2

1. Resource r2 which is not critical is online status.
2. When resource r2 get failed, resource r1 will be taken offline because it dependent on resource r2.
3. As r2 resource is not critical, group failover will be not performed. Therefore, the group will be partial online status.

RestartLimit Attribute

RestartLimit is an attribute of the resource type. This value determines how many times the recovery will be attempted until it is finally confirmed that it is failure. 
(Please refer to "Chapter 7. Resource" for more details.)

[Figure] Example of Failure Occur 3

1. On the assumption that the value of RestartLimit is 1 for resource r2, the first failure has occurred.
2. 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.
3. resource r2 restart.
4. resource r1 online.
5. When another failure occurs on resource r2, all of the resource will be taken offline from resource r1 to r3 by order.
6. Resource r3 will be taken offline.
7. As a result, resource r2 is considered as failure and all resources in the group is offline status in the node.