Ban

Definition

Signature

ban(vs : set<VM>, ns : set<server>)

• vs : an non-empty set of VMs for a meaningful constraint. VMs not in the Running state are ignored.

• ns : an non-empty set of servers for a meaningful constraint. Servers not in the Online state are ignored.

The ban constraint disallows each running VM in vs to be hosted on any of the online servers in ns.

Classification

• Primary users: datacenter administrator
• Manipulated elements: VM placement
• Concerns: Maintenance, Partitioning, VM-to-server placement

Usage

This constraint may be use by the datacenter administrator to prepare servers for a software maintenance. In this situation, the administrator must first be sure that the servers do not host any running VMs to prevent a misconfiguration from altering them. Every running VM on these servers must then be relocated elsewhere while the other VMs should not be relocated on the servers to put into maintenance. A datacenter administrator may rely on a ban constraint to achieve that purpose. In this setting, all the VMs in the datacenter are given in parameters in addition to the servers to put into maintenance. At the end of the reconfiguration, no VMs will be running on the servers. Once the maintenance operation is terminated, the constraint may be removed to put the servers back into the hosting pool.

For partitioning reasons, some VMs may be disallowed to be running on some servers. As an example, servers may be dedicated to run service VMs. In this setting, the client VMs must not be allowed to run on the servers dedicated to run service VMs. Ban constraints may then be used by the datacenter administrator for that purpose.

Example

Figure 2 depicts a sample reconfiguration between a source and a destination configuration. In this example, the following ban constraints were considered:

N1: VM1 VM2

N2: VM4 VM3

N3:

N1: VM1

N2: (VM3)

N3: VM2 VM4

Figure 2: A reconfiguration motivated by ban constraints.

• ban({VM1, VM2, VM4}, {N2}). This constraint was not satisfied in the source configuration as VM4 was running on N2. The reconfiguration fixed this violation by relocating VM4 to N3.

• ban({VM3}, {N2}). This constraint was not satisfied in the source configuration. However it is satisfied in the destination configuration as VM3 is no longer running.

• ban({VM1, VM2}, {N2}). This constraint was satisfied in the source configuration. It is still satisfied in the destination configuration as the relocation of VM2 is compatible with this constraint.

See also

Related Constraints

• fence: the opposite constraint of ban. One ban constraint can be emulated using a fence constraint by specifying to the fence constraint, the absolute complement of the set of servers specified in the ban constraint.

• quarantine. The quarantine constraint may also be used to prepare a software maintenance on servers when relocation is not possible. In this setting, the given servers will be ready for the maintenance once their VMs are terminated.

Reformulation(s)

• Using fence: ban(vs1, ns1) ↔ fence(vs1,ns1)

• Using among: ban(vs1, ns1) ↔ among(vs1,{ns1})

Specialization(s)

• To fence: ban(vs1,ns1) ↔ fence(vs1, ns1)