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This chapter is from the book

This chapter is from the book

Resource Reservation

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How can shared IT resources be protected from confl icts that can arise from concurrent access?

Problem

When two or more cloud service consumers attempt to instantiate the same shared IT resource, runtime confl icts can occur, including resource constraints due to lack of capacity.

Solution

A system is established whereby a portion of an IT resource (or one or more IT resources) is set aside exclusively for a given cloud service consumer.

Application

The resource management system is used to defi ne IT resource thresholds and to restrict access to reserved IT resources.

Mechanisms

Audit Monitor, Cloud Storage Device, Cloud Usage Monitor, Hypervisor, Logical Network Perimeter, Remote Administration System, Resource Management System, Resource Replication, Virtual CPU, Virtual Infrastructure Manager (VIM), Virtual RAM, Virtual Server

Problem

When applying Shared Resources (17) and Resource Pooling (99) we can give multiple cloud service consumers access to the same IT resources. Depending on how IT resources are designed for shared usage and depending on their available levels of capacity, concurrent access can lead to a runtime exception condition called resource constraint.

A resource constraint is a condition that occurs when two or more cloud consumers have been allocated to share an IT resource that does not have the capacity to accommodate the entire processing requirements of the cloud consumers. As a result, one or more of the consumers will encounter degraded performance or be rejected altogether. The cloud service itself may go down, resulting in all cloud consumers being rejected.

Other types of runtime conflicts can occur when an IT resource (especially one not specifically designed to accommodate sharing) is concurrently accessed by different cloud service consumers. For example, nested and sibling resource pools introduce the notion of resource borrowing, whereby one pool can temporarily borrow IT resources from other pools. A runtime conflict can be triggered when the borrowed IT resource is not returned due to prolonged usage by the cloud service consumer that is borrowing it. This can inevitably lead back to the occurrence of resource constraints.

Solution

An IT resource reservation system is established to protect cloud service consumers (“tenants”) sharing the same underlying IT resources from each other. This system essentially guarantees a minimum amount of an IT resource for each cloud consumer by putting it aside and making it exclusively available only to the designated cloud service consumer. Potential conflicts, such as resource constraints and resource borrowing, are avoided because the reserved IT resources are never actually shared.

Application

Creating an IT resource reservation system requires the involvement of the resource management system mechanism that can be used to define IT resource usage thresholds for individual IT resources and resource pools. Reservations are created to lock the amount of IT resources that each pool must keep. The balance of IT resources within a pool can still be shared (and borrowed).

The following steps are shown in Figures 4.4 to 4.6:

  1. A physical resource group is created.
  2. A parent resource pool is created from the physical resource group by applying Resource Pooling (99).
  3. Two smaller child pools are created from the parent resource pool, and resource limits are defined using the resource management system mechanism.
  4. Cloud consumers are provided with access to their own exclusive resource pools.
  5. There is an increase in requests from Cloud Consumer A, resulting in more IT resources being allocated.
  6. Consequently, some IT resources are borrowed from Pool 2. The amount of borrowed resources, however, is pre-determined by the resource limit defined in Step 3, which ensures that Cloud Consumer B will not face resource constraints.
  7. Cloud Consumer B now imposes more requests and usage demands and may soon need to utilize all available IT resources in the pool.
  8. The resource management system forces Pool 1 to release the IT resources and move them back to Pool 2 to become available for Cloud Consumer B.

    Figure 4.4

    Figure 4.4 A resource pool hierarchy to which an IT resource reservation system is applied (Part I).

    Figure 4.5

    Figure 4.5 A resource pool hierarchy to which an IT resource reservation system is applied (Part II).

    Figure 4.6

    Figure 4.6 A resource pool hierarchy to which an IT resource reservation system is applied (Part III).

Mechanisms

  • Audit Monitor – The audit monitor may be responsible for ensuring that the resource reservation system is acting in compliance with cloud consumer auditing, privacy, and other regulatory requirements. The audited information may also pertain to the geographical location of the reserved IT resources.
  • Cloud Storage Device – This mechanism may be an IT resource reserved by this system.
  • Cloud Usage Monitor – A cloud usage monitor may be involved with monitoring thresholds that trigger the allocation of reserved IT resources.
  • Hypervisor – The hypervisor mechanism is associated with this pattern in its commitment to applying reservations for different cloud consumers in order to ensure that they are allocated the guaranteed amounts of IT resources. In support of this, it is responsible for locking, and pre-allocating the virtual servers’ reserved computing capacity based on their configurations.
  • Logical Network Perimeter – This mechanism ensures that reserved IT resources are made exclusively available to the appropriate cloud consumers.
  • Remote Administration System – This system provides the tools necessary for custom front-ends to provide the administration controls necessary for cloud consumers to create and manage reserved IT resource allocations.
  • Resource Management System – The resource management system provides essential features for managing IT resource reservations. These features may be encapsulated by a portal produced via the remote administration system mechanism.
  • Resource Replication – The resource replication mechanism needs to stay updated on any cloud consumer IT resource consumption limitations to determine when new IT resource instances need to be replicated and provisioned.
  • Virtual CPU – This mechanism is used to define the computing capacity a virtual server needs to have reserved. When this mechanism is used, a specific amount of CPU is explicitly allocated to each virtual server and not shared with other virtual servers.
  • Virtual Infrastructure Manager (VIM) – This mechanism is used to configure the resources that are reserved for each virtual server.
  • Virtual RAM – This mechanism is used to configure the memory that virtual servers need reserved and guaranteed. The memory that is reserved for each virtual server is not allocated to or shared with other virtual servers.
  • Virtual Server – This mechanism hosts the reserved IT resources that are allocated.
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