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.
# File lib/rbvmomi/utils/admission_control.rb, line 46 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 @logger = opts[:logger] end
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 136 def computers if !@computers @computers = @computer_names.map do |name| computer = datacenter.find_compute_resource(name) [computer, computer.stats] end end @computers end
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 102 def datacenter if !@datacenter @datacenter = @root_folder.traverse(@datacenter_path, VIM::Datacenter) if !@datacenter fail "datacenter #{@datacenter_path} not found" end end @datacenter end
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 334 def datastore placementHint = nil if @datastore return @datastore end 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
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 116 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
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 218 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
# File lib/rbvmomi/utils/admission_control.rb, line 69 def log x if @logger @logger.info x else puts "#{Time.now}: #{x}" end end
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 367 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' => %w(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
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 304 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
Returns all candidate datastores for a given pod. @return [Array] List of VIM::Datastore
# File lib/rbvmomi/utils/admission_control.rb, line 210 def pod_datastores pod pod.first.datastore & self.datastores end
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 169 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: %w(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
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 149 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
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 81 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