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Fabien Hermenier edited this page Mar 20, 2013 · 95 revisions

Getting started

[Associated source code] (https://github.com/fhermeni/btrplace-solver/blob/develop/examples/src/main/java/btrplace/examples/GettingStarted.java)

Btrplace is a flexible algorithm to place Virtual Machines (VMs) on servers in a hosting platforms. Basically, it manages VMs with respect to constraints that are stated by the users. As a user of the algorithm, you only have to declare the constraints you want to have satisfied. This tutorial presents the fundaments of BtrPlace.

BtrPlace is articulated around 4 primitives:

  • The model depicts the current state of a virtualized hosting platforms. It is usually generated from monitoring data

  • A reconfiguration plan. A plan consists of a scheduled set of actions to execute. A plan allows to transit from a source model to a destination model.

  • A set of Satisfaction Oriented Constraints ( SatConstraints). A SatConstraint imposes a restriction on a model or a reconfiguration. On a model, it provides a discrete restriction. On a plan, it imposes a continuous restriction. Basically, it allows to control the state of the elements (VMs, servers), the resource allocation, the VMs placement, ...

  • A reconfiguration algorithm is an algorithm that takes a model and a set of constraints as a parameter. It checks if the model is consistent with regards to the states constraints. If not, it computes a plan to reach a model that satisfies all the constraints simultaneously.

Defining a model

A model is composed of several elements:

In this tutorial, we will reproduce the model that is depicted by the figure on the left. It represents a model composed by 4 online servers hosting 6 running VMs.

The mapping###

In Btrplace, as in many hypervisors, elements such as servers and VMs are identified by a UUID. The next snippet creates a mapping that declare the online node n1 and place VMs vm2 and vm3 on it:

Mapping m = new DefaultMapping();

UUID n1 = UUID.randomUUID();
UUID vm2 = UUID.randomUUID();
UUID vm3 = UUID.randomUUID();
//n1 is online
map.addOnlineNode(n1);

//vm3 and vm2 runs on n1
map.addRunningVM(vm3, n1);
map.addRunningVM(vm2, n1);

Describing the current resource usage with Views##

In Btrplace, a resource is defined using a special view called ShareableResource. This allows to specify the physical resource capacity of the nodes and the virtual resource usage of the VMs.

Below is the snippet to declare a resource called "cpu".For this example, itindicates the number of physical CPUs available on n1, and the number of virtual CPUs that are allocated to vm2 and vm3.

        ShareableResource rcCPU = new ShareableResource("cpu");
        //n1 has 8 physical CPUs
        rcCPU.set(n1, 8);
        
        //vm2 has 3 virtual CPUs
        rcCPU.set(vm2, 3);
        //vm3 has 3 virtual CPUs
        rcCPU.set(vm3, 4);

Building the resulting model

Model mo = new DefaultModel(map);
mo.attach(rcCPU);

Stating constraints

Constraints are independant elements that impose a restriction on a model. Typically, it may restrict the VMs placement, their state, their resource allocation, ...

The following code creates a set of 5 constraints

  Set<SatConstraint> cstrs = new HashSet<SatConstraint>();

  //We disallow CPU overbooking, so each unit of
  //virtual resource consumes one unit of physical
  //resource on every nodes
  Set<UUID> allNodes = new HashSet<UUID>(Arrays.asList(n1, n2, n3, n4));
  cstrs.add(new Overbook(allNodes, "cpu", 1));      

  //VM2 and VM3 must be running on distinct nodes
  cstrs.add(new Spread(new HashSet<UUID>(Arrays.asList(vm2, vm3))));

  //VM1 must have at least 3 virtual CPU dedicated to it
  cstrs.add(new Preserve(Collections.singleton(vm1), "cpu", 3));

  //node N4 must be offline
  cstrs.add(new Offline(Collections.singleton(n4)));

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