DOC: Key Concepts and Objects

Experiment: A sequence of CBTOOL directives (with start times and duration for each execution), processed and executed sequentially.

An experiment is composed by a set of Experiment Objects. Experiment objects are defined within CBTOOL, and used by it to control the effective deployment and execution of benchmark applications.

Objects are of three classes.

• The configuration objects are used by CBTOOL for environment configuration and experiment execution customization. The parameters of these objects control several aspects of the CBTOOL execution (e.g., the IP address of the node that executes the Metric Store, what is the default polling interval for provisioning operations, the location of the ssh private keys used to connect to the VMs). These objects are also know internally as global objects, since all other objects ( concrete and abstract have parameters derived from "templates" on configuration objects.
• The concrete objects are managed and tracked by both CBTOOL and the cloud manager.
• The abstract objects are the ones whose meaning and state are tracked only by CBTOOL, representing a logical aggregation of the multiple instances of concrete objects. Abstract objects can represent either a single Virtual Application deployed on a cloud, or a group of inter-related VApps. It is through the specification of abstract objects that an experiment assumes a truly dynamic behavior.

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Concrete Objects are of four flavors: Clouds, Virtual Machine Containers (VMCs), Hosts (exposed by some Clouds) and Virtual Machines (VMs).

Cloud: The Cloud object represents the cloud manager, and includes in its description all information required to establish a connection to it, including access and authentication credentials.

• By having a whole cloud as an object, CloudBench allows one direct an individual experiment plan at multiple clouds to compare them against each other.

Virtual Machine Container (VMC): The smallest point of access or "place" where a VM is instantiated.

• Each VMC has a cloud-wide unique identifier
• While the meaning of VMC is invariant, its scope is very specific to each particular cloud. It can range from a single host (in a virtualized environment with the libvirt/KVM duo) to a whole geographic region with multiple “availability zones” (in the case of Amazon’s Elastic Compute Cloud).
• The definition of the VMC as a distinct object is useful, allowing CBTOOL to exploit intra-cloud parallelism (e.g., in a geographically distributed cloud)

Host: Individual Hypervisors where VMs are effectively deployed.

• Not all clouds allow Hosts to be discovered/monitored (e.g., Amazon EC2)

Virtual Machine (VM): Individual Virtual Machine instances are the only element whose state (i.e., created, running, destroyed) are effectively know by a given cloud.

• VMs are instantiated and terminated (the latter only in case of an VAppS, with a variable number of instances) by the submission of the appropriate commands/operations/requests to the cloud by CBTOOL.
• In order to be properly created, a VM with a given role needs to be fully identified within the cloud, with some cloud-specific information, like image id, instance size and/or class. This is designated a VM template.

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Abstract Objects are of two flavors: Virtual Applications and Virtual Application Submitters

Virtual Application Submitter (VAppS): A collection of Application Instances of a given Application Type.

• Due to "historical" reasons, this abstraction is also called Application Instance Deployment Request Submitter (AIDRS).
• Every Virtual Application instance has an inter-arrival time, and a lifetime, governed by two AS-wide random distributions.
• Every Virtual Application instance on an VAppS has an individual time-varying load intensity and duration attributed to it, according to two AS-wide random distributions.

Virtual Application (VApp): A collection of VMs that run cooperatively to effectively execute a given application type.

• Due to "historical" reasons, this abstraction is also called Application Instance (AI)
• Every VM has a “role” within the VApp.
• One of the VMs has to have the roles load manager and metrics aggregator. This VM will: (1) manage the load applied to the rest of the AI and (2) collect performance data from the VApp.
• Each VApp has an “ Virtual Application template ”, containing a list of VM roles and its topology.