This pull request (PR) implements a Distributed Resource Scheduler (DRS) for a CloudStack cluster. The primary objective of this feature is to enable automatic resource optimization and workload balancing within the cluster by live migrating the VMs as per configuration.
Administrators can also execute DRS manually for a cluster, using the UI or the API.
Adds support for two algorithms - condensed & balanced. Algorithms are pluggable allowing ACS Administrators to have customized control over scheduling.
Implementation
There are three top level components:
Scheduler
A timer task which:
Generate DRS plan for clusters
Process DRS plan
Remove old DRS plan records
DRS Execution
We go through each VM in the cluster and use the specified algorithm to check if DRS is required and to calculate cost, benefit & improvement of migrating that VM to another host in the cluster. On the basis of cost, benefit & improvement, the best migration is selected for the current iteration and the VM is migrated. The maximum number of iterations (live migrations) possible on the cluster is defined by drs.iterations which is defined as a percentage (as a value between 0 and 1) of total number of workloads.
Algorithm
Every algorithms implements two methods:
needsDrs - to check if drs is required for cluster
getMetrics - to calculate cost, benefit & improvement of a migrating a VM to another host.
Algorithms
Condensed - Packs all the VMs on minimum number of hosts in the cluster.
Balanced - Distributes the VMs evenly across hosts in the cluster.
Algorithms use drs.level to decide the amount of imbalance to allow in the cluster.
APIs Added
listClusterDrsPlan
id - ID of the DRS plan to list
clusterid - to list plans for a cluster id
generateClusterDrsPlan
id - cluster id
iterations - The maximum number of iterations in a DRS job defined as a percentage (as a value between 0 and 1) of total number of workloads. Defaults to value of cluster's drs.iterations setting.
executeClusterDrsPlan
id - ID of the cluster for which DRS plan is to be executed.
migrateto - This parameter specifies the mapping between a vm and a host to migrate that VM. Format of this parameter: migrateto[vm-index].vm=<uuid>&migrateto[vm-index].host=<uuid>.
Config Keys Added
ClusterDrsPlanExpireInterval
Key drs.plan.expire.interval
Scope Global
Default Value 30 days
Description The interval in days after which old DRS records will be cleaned up.
ClusterDrsEnabled
Key drs.automatic.enable
Scope Cluster
Default Value false
Description Enable/disable automatic DRS on a cluster.
ClusterDrsInterval
Key drs.automatic.interval
Scope Cluster
Default Value 60 minutes
Description The interval in minutes after which a periodic background thread will schedule DRS for a cluster.
ClusterDrsIterations
Key drs.max.migrations
Scope Cluster
Default Value 50
Description Maximum number of live migrations in a DRS execution.
ClusterDrsAlgorithm
Key drs.algorithm
Scope Cluster
Default Value condensed
Description DRS algorithm to execute on the cluster. This PR implements two algorithms - balanced & condensed.
ClusterDrsLevel
Key drs.imbalance
Scope Cluster
Default Value 0.5
Description Percentage (as a value between 0.0 and 1.0) of imbalance allowed in the cluster. 1.0 means no imbalance
is allowed and 0.0 means imbalance is allowed.
ClusterDrsMetric
Key drs.imbalance.metric
Scope Cluster
Default Value memory
Description The cluster imbalance metric to use when checking the drs.imbalance.threshold. Possible values are memory and cpu.
