AdmissionControlledResourceScheduler

An admission controlled resource scheduler for large scale vSphere deployments

While DRS (Dynamic Resource Scheduler) in vSphere handles CPU and Memory allocations within a single vSphere cluster, larger deployments require another layer of scheduling to make the use of multiple clusters transparent. So this class doesn't replace DRS, but in fact works on top of it.

The scheduler in this class performs admission control to make sure clusters don't get overloaded. It does so by adding additional metrics to the already existing CPU and Memory reservation system that DRS has. After admission control it also performs very basic initial placement. Note that in-cluster placement and load-balancing is left to DRS. Also note that no cross-cluster load balancing is done.

This class uses the concept of a Pod: A set of clusters that share a set of datastores. From a datastore perspective, we are free to place a VM on any host or cluster. So admission control is done at the Pod level first. Pods are automatically dicovered based on lists of clusters and datastores.

Admission control covers the following metrics:

Host availability: If no hosts are available within a cluster or pod, admission is denied.
Minimum free space: If a datastore falls below this free space percentage, admission to it will be denied. Admission to a pod is granted as long at least one datastore passes admission control.
Maximum number of VMs: If a Pod exceeds a configured number of powered on VMs, admission is denied. This is a crude but effective catch-all metric in case users didn't set proper individual CPU or Memory reservations or if the scalability limit doesn't originate from CPU or Memory.

Placement after admission control:

Cluster selection: A load metric based on a combination of CPU and Memory load is used to always select the "least loaded" cluster. The metric is very crude and only meant to do very rough load balancing. If DRS clusters are large enough, this is good enough in most cases though.
Datastore selection: Right now NO intelligence is implemented here.

Usage: Instantiate the class, call make_placement_decision and then use the exposed computer (cluster), resource pool, vm_folder and datastore. Currently once computed, a new updated placement can't be generated.

Public Class Methods

new(vim, opts = {}) click to toggle source

# File lib/rbvmomi/utils/admission_control.rb, line 44
def initialize vim, opts = {}
  @vim = vim
  
  @datacenter = opts[:datacenter]
  @datacenter_path = opts[:datacenter_path]
  @vm_folder = opts[:vm_folder]
  @vm_folder_path = opts[:vm_folder_path]
  @rp_path = opts[:rp_path]
  @computers = opts[:computers]
  @computer_names = opts[:computer_names]
  @datastores = opts[:datastores]
  @datastore_paths = opts[:datastore_paths]
  
  @max_vms_per_pod = opts[:max_vms_per_pod]
  @min_ds_free = opts[:min_ds_free]
  @service_docs_url = opts[:service_docs_url]
  
  @pc = @vim.serviceContent.propertyCollector
  @root_folder = @vim.serviceContent.rootFolder
end

Public Instance Methods

computers() click to toggle source

Returns the candidate computers (aka clusters). If not set yet, uses the computer_names to look them up. @return [Array] List of [VIM::ClusterComputeResource, Hash] tuples, where

the Hash is a list of stats about the computer

# File lib/rbvmomi/utils/admission_control.rb, line 128
def computers
  if !@computers
    @computers = @computer_names.map do |name|
      computer = datacenter.find_compute_resource(name)
      [computer, computer.stats]
    end
  end
  @computers
end

datacenter() click to toggle source

Returns the used Datacenter. If not set yet, uses the datacenter_path to lookup the datacenter. @return [VIM::Datacenter] The datacenter

# File lib/rbvmomi/utils/admission_control.rb, line 94
def datacenter
  if !@datacenter
    @datacenter = @root_folder.traverse(@datacenter_path, VIM::Datacenter) 
    if !@datacenter 
      fail "datacenter #{@datacenter_path} not found"
    end
  end
  @datacenter
end

datastore(placementHint = nil) click to toggle source

Returns the datastore to be used for placement. If not set yet, picks a datastore without much intelligence, as long as it passes admission control. @return [VIM::Datastore] Chosen datastore

# File lib/rbvmomi/utils/admission_control.rb, line 326
def datastore placementHint = nil
  pod_datastores = pick_computer.datastore & datastores

  eligible = pod_datastores.select do |ds|
    min_ds_free = @min_ds_free
    if min_ds_free && min_ds_free > 0
      ds_sum = @datastore_props[ds]['summary']
      free_percent = ds_sum.freeSpace.to_f * 100 / ds_sum.capacity    
      free_percent > min_ds_free
    else
      true
    end
  end

  if eligible.length == 0
    fail "Couldn't find any eligible datastore. Admission control should have prevented this"
  end
  
  if placementHint && placementHint > 0
    @datastore = eligible[placementHint % eligible.length]
  else
    @datastore = eligible.first
  end  
  @datastore
end

datastores() click to toggle source

Returns the candidate datastores. If not set yet, uses the datastore_paths to lookup the datastores under the datacenter. As a side effect, also looks up properties about all the datastores @return [Array] List of VIM::Datastore

# File lib/rbvmomi/utils/admission_control.rb, line 108
def datastores
  if !@datastores
    @datastores = @datastore_paths.map do |path|
      ds = datacenter.datastoreFolder.traverse(path, VIM::Datastore)
      if !ds 
        fail "datastore #{path} not found"
      end
      ds
    end
  end
  if !@datastore_props
    @datastore_props = @pc.collectMultiple(@datastores, 'summary', 'name')
  end
  @datastores
end

filtered_pods() click to toggle source

Returns the list of pods that pass admission control. If not set yet, performs admission control to compute the list. If no pods passed the admission control, an exception is thrown. @return [Array] List of pods, where a pod is a list of VIM::ClusterComputeResource

# File lib/rbvmomi/utils/admission_control.rb, line 210
def filtered_pods
  # This function applies admission control and returns those pods that have
  # passed admission control. An exception is thrown if access was denied to 
  # all pods.
  if !@filtered_pods
    log "Performing admission control:"
    @filtered_pods = self.pods.select do |pod|
      # Gather some statistics about the pod ...
      on_vms = pod_vms(pod).select{|k,v| v['runtime.powerState'] == 'poweredOn'}
      num_pod_vms = on_vms.length
      pod_datastores = self.pod_datastores(pod)
      log "Pod: #{pod.map{|x| x.name}.join(', ')}"
      log "   #{num_pod_vms} VMs"
      pod_datastores.each do |ds|
        ds_sum = @datastore_props[ds]['summary']
        @datastore_props[ds]['free_percent'] = ds_sum.freeSpace.to_f * 100 / ds_sum.capacity
      end
      pod_datastores.each do |ds|
        ds_props = @datastore_props[ds]
        ds_name = ds_props['name']
        free = ds_props['free_percent']
        free_gb = ds_props['summary'].freeSpace.to_f / 1024**3
        free_str = "%.2f GB (%.2f%%)" % [free_gb, free]
        log "   Datastore #{ds_name}: #{free_str} free"
      end
      
      # Admission check: VM limit
      denied = false
      max_vms = @max_vms_per_pod
      if max_vms && max_vms > 0
        if num_pod_vms > max_vms
          err = "VM limit (#{max_vms}) exceeded on this Pod"
          denied = true
        end
      end
  
      # Admission check: Free space on datastores
      min_ds_free = @min_ds_free
      if min_ds_free && min_ds_free > 0
        # We need at least one datastore with enough free space
        low_list = pod_datastores.select do |ds|
          @datastore_props[ds]['free_percent'] <= min_ds_free
        end
        
        if low_list.length == pod_datastores.length
          dsNames = low_list.map{|ds| @datastore_props[ds]['name']}.join(", ")
          err = "Datastores #{dsNames} below minimum free disk space (#{min_ds_free}%)"
          denied = true
        end
      end
      
      # Admission check: Hosts are available
      if !denied
        hosts_available = pod.any? do |computer|
          stats = Hash[self.computers][computer]
          stats[:totalCPU] > 0 && stats[:totalMem] > 0
        end
        if !hosts_available
          err = "No hosts are current available in this pod"
          denied = true
        end
      end
  
      if denied    
        log "   Admission DENIED: #{err}"
      else
        log "   Admission granted"
      end
      
      !denied
    end
  end
  if @filtered_pods.length == 0
    log "Couldn't find any Pod with enough resources."
    if @service_docs_url
      log "Check #{@service_docs_url} to see which other Pods you may be able to use"
    end
    fail "Admission denied"
  end
  @filtered_pods
end

log(x) click to toggle source

# File lib/rbvmomi/utils/admission_control.rb, line 65
def log x
  puts "#{Time.now}: #{x}"
end

make_placement_decision(opts = {}) click to toggle source

Runs the placement algorithm and populates all the various properties as a side effect. Run this first, before using the other functions of this class.

# File lib/rbvmomi/utils/admission_control.rb, line 355
def make_placement_decision opts = {}
  self.filtered_pods
  self.pick_computer opts[:placementHint]
  log "Selected compute resource: #{@computer.name}"

  @rp = @computer.resourcePool.traverse(@rp_path)
  if !@rp 
    fail "Resource pool #{@rp_path} not found"
  end
  log "Resource pool: #{@rp.pretty_path}"

  stats = @computer.stats
  if stats[:totalMem] > 0 && stats[:totalCPU] > 0
    cpu_load = "#{(100*stats[:usedCPU])/stats[:totalCPU]}% cpu"
    mem_load = "#{(100*stats[:usedMem])/stats[:totalMem]}% mem"
    log "Cluster utilization: #{cpu_load}, #{mem_load}"
  end
      
  user_vms = vm_folder.inventory_flat('VirtualMachine' => %(name storage)).select do |k, v| 
    k.is_a?(RbVmomi::VIM::VirtualMachine)
  end
  numVms = user_vms.length
  unshared = user_vms.map do |vm, info| 
    info['storage'].perDatastoreUsage.map{|x| x.unshared}.inject(0, &:+)
  end.inject(0, &:+)
  log "User stats: #{numVms} VMs using %.2fGB of storage" % [unshared.to_f / 1024**3]
  
  @placement_hint = opts[:placement_hint] || (rand(100) + 1)
  datastore = self.datastore @placement_hint
  log "Datastore: #{datastore.name}"
end

pick_computer(placementhint = nil) click to toggle source

Returns the computer (aka cluster) to be used for placement. If not set yet, computs the least loaded cluster (using a metric that combines CPU and Memory load) that passes admission control. @return [VIM::ClusterComputeResource] Chosen computer (aka cluster)

# File lib/rbvmomi/utils/admission_control.rb, line 296
def pick_computer placementhint = nil
  if !@computer
    # Out of the pods to which we have been granted access, pick the cluster
    # (aka computer) with the lowest CPU/Mem utilization for load balancing
    available = self.filtered_pods.flatten
    eligible = self.computers.select do |computer,stats|
      available.member?(computer) && stats[:totalCPU] > 0 and stats[:totalMem] > 0
    end
    computer = nil
    if placementhint
      if eligible.length > 0
        computer = eligible.map{|x| x[0]}[placementhint % eligible.length]
      end
    else
      computer, = eligible.min_by do |computer,stats|
        2**(stats[:usedCPU].to_f/stats[:totalCPU]) + (stats[:usedMem].to_f/stats[:totalMem])
      end
    end
  
    if !computer 
      fail "No clusters available, should have been prevented by admission control"
    end
    @computer = computer
  end
  @computer
end

pod_datastores(pod) click to toggle source

Returns all candidate datastores for a given pod. @return [Array] List of VIM::Datastore

# File lib/rbvmomi/utils/admission_control.rb, line 202
def pod_datastores pod
  pod.first.datastore & self.datastores
end

pod_vms(pod) click to toggle source

Returns all VMs residing with a pod. Doesn't account for templates. Does so very efficiently using a single API query. @return [Hash] Hash of VMs as keys and their properties as values.

# File lib/rbvmomi/utils/admission_control.rb, line 161
def pod_vms pod
  # This function retrieves all VMs residing inside a pod
  filterSpec = VIM.PropertyFilterSpec(
    objectSet: pod.map do |computer, stats|
      {
        obj: computer.resourcePool,
        selectSet: [
          VIM.TraversalSpec(
            name: 'tsFolder',
            type: 'ResourcePool',
            path: 'resourcePool',
            skip: false,
            selectSet: [
              VIM.SelectionSpec(name: 'tsFolder'),
              VIM.SelectionSpec(name: 'tsVM'),
            ]
          ),
          VIM.TraversalSpec(
            name: 'tsVM',
            type: 'ResourcePool',
            path: 'vm',
            skip: false,
            selectSet: [],
          )
        ]
      }
    end,
    propSet: [
      { type: 'ResourcePool', pathSet: ['name'] },
      { type: 'VirtualMachine', pathSet: %(runtime.powerState) }
    ]
  )

  result = @vim.propertyCollector.RetrieveProperties(specSet: [filterSpec])

  out = result.map { |x| [x.obj, Hash[x.propSet.map { |y| [y.name, y.val] }]] }
  out.select{|obj, props| obj.is_a?(VIM::VirtualMachine)}
end

pods() click to toggle source

Returns the candidate pods. If not set, automatically computes the pods based on the list of computers (aka clusters) and datastores. @return [Array] List of pods, where a pod is a list of VIM::ClusterComputeResource

# File lib/rbvmomi/utils/admission_control.rb, line 141
def pods
  if !@pods
    # A pod is defined as a set of clusters (aka computers) that share the same
    # datastore accessibility. Computing pods is done automatically using simple
    # set theory math.
    computersProps = @pc.collectMultiple(computers.map{|x| x[0]}, 'datastore')
    @pods = computers.map do |computer, stats|
      computersProps[computer]['datastore'] & self.datastores
    end.uniq.map do |ds_list|
      computers.map{|x| x[0]}.select do |computer|
        (computer.datastore & self.datastores) == ds_list
      end
    end
  end
  @pods  
end

vm_folder() click to toggle source

Returns the used VM folder. If not set yet, uses the vm_folder_path to lookup the folder. If it doesn't exist, it is created. Collisions between multiple clients concurrently creating the same folder are handled. @return [VIM::Folder] The VM folder

# File lib/rbvmomi/utils/admission_control.rb, line 73
def vm_folder 
  retries = 1
  begin
    @vm_folder ||= datacenter.vmFolder.traverse!(@vm_folder_path, VIM::Folder)
    if !@vm_folder 
      fail "VM folder #{@vm_folder_path} not found"
    end
  rescue RbVmomi::Fault => fault
    if !fault.fault.is_a?(RbVmomi::VIM::DuplicateName)
      raise
    else
      retries -= 1
      retry if retries >= 0 
    end 
  end
  @vm_folder    
end

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