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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.vespa.hosted.provision.autoscale;
import com.yahoo.config.provision.ClusterResources;
import com.yahoo.config.provision.NodeResources;
import com.yahoo.vespa.hosted.provision.Node;
import com.yahoo.vespa.hosted.provision.NodeList;
import com.yahoo.vespa.hosted.provision.NodeRepository;
import com.yahoo.vespa.hosted.provision.applications.Application;
import com.yahoo.vespa.hosted.provision.applications.AutoscalingStatus;
import com.yahoo.vespa.hosted.provision.applications.AutoscalingStatus.Status;
import com.yahoo.vespa.hosted.provision.applications.Cluster;
import java.time.Duration;
import java.time.Instant;
import java.util.Objects;
import java.util.Optional;
/**
* The autoscaler gives advice about what resources should be allocated to a cluster based on observed behavior.
*
* @author bratseth
*/
public class Autoscaler {
/** What cost difference is worth a reallocation? */
private static final double costDifferenceWorthReallocation = 0.1;
/** What resource difference is worth a reallocation? */
private static final double resourceDifferenceWorthReallocation = 0.03;
private final NodeRepository nodeRepository;
private final AllocationOptimizer allocationOptimizer;
public Autoscaler(NodeRepository nodeRepository) {
this.nodeRepository = nodeRepository;
this.allocationOptimizer = new AllocationOptimizer(nodeRepository);
}
/**
* Suggest a scaling of a cluster. This returns a better allocation (if found)
* without taking min and max limits into account.
*
* @param clusterNodes the list of all the active nodes in a cluster
* @return scaling advice for this cluster
*/
public Advice suggest(Application application, Cluster cluster, NodeList clusterNodes) {
return autoscale(application, cluster, clusterNodes, Limits.empty());
}
/**
* Autoscale a cluster by load. This returns a better allocation (if found) inside the min and max limits.
*
* @param clusterNodes the list of all the active nodes in a cluster
* @return scaling advice for this cluster
*/
public Advice autoscale(Application application, Cluster cluster, NodeList clusterNodes) {
if (cluster.minResources().equals(cluster.maxResources()))
return Advice.none(Status.unavailable, "Autoscaling is not enabled");
return autoscale(application, cluster, clusterNodes, Limits.of(cluster));
}
private Advice autoscale(Application application, Cluster cluster, NodeList clusterNodes, Limits limits) {
ClusterModel clusterModel = new ClusterModel(application,
clusterNodes.clusterSpec(),
cluster,
clusterNodes,
nodeRepository.metricsDb(),
nodeRepository.clock());
if ( ! clusterIsStable(clusterNodes, nodeRepository))
return Advice.none(Status.waiting, "Cluster change in progress");
if (scaledIn(clusterModel.scalingDuration(), cluster))
return Advice.dontScale(Status.waiting,
"Won't autoscale now: Less than " + clusterModel.scalingDuration() +
" since last resource change");
if (clusterModel.nodeTimeseries().measurementsPerNode() < minimumMeasurementsPerNode(clusterModel.scalingDuration()))
return Advice.none(Status.waiting,
"Collecting more data before making new scaling decisions: Need to measure for " +
clusterModel.scalingDuration() + " since the last resource change completed, " +
clusterModel.nodeTimeseries().measurementsPerNode() + " measurements per node found," +
" need at least " + minimumMeasurementsPerNode(clusterModel.scalingDuration()));
if (clusterModel.nodeTimeseries().nodesMeasured() != clusterNodes.size())
return Advice.none(Status.waiting,
"Collecting more data before making new scaling decisions:" +
" Have measurements from " + clusterModel.nodeTimeseries().nodesMeasured() +
" nodes, but require from " + clusterNodes.size());
var currentAllocation = new AllocatableClusterResources(clusterNodes.asList(), nodeRepository);
Optional<AllocatableClusterResources> bestAllocation =
allocationOptimizer.findBestAllocation(clusterModel.loadAdjustment(), currentAllocation, clusterModel, limits);
if (bestAllocation.isEmpty())
return Advice.dontScale(Status.insufficient, "No allocations are possible within configured limits");
if (! worthRescaling(currentAllocation.realResources(), bestAllocation.get().realResources())) {
if (bestAllocation.get().fulfilment() < 1)
return Advice.dontScale(Status.insufficient, "Configured limits prevents better scaling of this cluster");
else
return Advice.dontScale(Status.ideal, "Cluster is ideally scaled");
}
if (isDownscaling(bestAllocation.get(), currentAllocation) && scaledIn(clusterModel.scalingDuration().multipliedBy(3), cluster))
return Advice.dontScale(Status.waiting,
"Waiting " + clusterModel.scalingDuration().multipliedBy(3) +
" since the last change before reducing resources");
return Advice.scaleTo(bestAllocation.get().advertisedResources());
}
public static boolean clusterIsStable(NodeList clusterNodes, NodeRepository nodeRepository) {
// The cluster is processing recent changes
if (clusterNodes.stream().anyMatch(node -> node.status().wantToRetire() ||
node.allocation().get().membership().retired() ||
node.allocation().get().removable()))
return false;
// A deployment is ongoing
if (nodeRepository.nodes().list(Node.State.reserved).owner(clusterNodes.first().get().allocation().get().owner()).size() > 0)
return false;
return true;
}
/** Returns true if it is worthwhile to make the given resource change, false if it is too insignificant */
public static boolean worthRescaling(ClusterResources from, ClusterResources to) {
// *Increase* if needed with no regard for cost difference to prevent running out of a resource
if (meaningfulIncrease(from.totalResources().vcpu(), to.totalResources().vcpu())) return true;
if (meaningfulIncrease(from.totalResources().memoryGb(), to.totalResources().memoryGb())) return true;
if (meaningfulIncrease(from.totalResources().diskGb(), to.totalResources().diskGb())) return true;
// Otherwise, only *decrease* if it reduces cost meaningfully
return ! similar(from.cost(), to.cost(), costDifferenceWorthReallocation);
}
private static boolean meaningfulIncrease(double from, double to) {
return from < to && ! similar(from, to, resourceDifferenceWorthReallocation);
}
private static boolean similar(double r1, double r2, double threshold) {
return Math.abs(r1 - r2) / (( r1 + r2) / 2) < threshold;
}
/** Returns true if this reduces total resources in any dimension */
private boolean isDownscaling(AllocatableClusterResources target, AllocatableClusterResources current) {
NodeResources targetTotal = target.advertisedResources().totalResources();
NodeResources currentTotal = current.advertisedResources().totalResources();
return ! targetTotal.justNumbers().satisfies(currentTotal.justNumbers());
}
private boolean scaledIn(Duration delay, Cluster cluster) {
return cluster.lastScalingEvent().map(event -> event.at()).orElse(Instant.MIN)
.isAfter(nodeRepository.clock().instant().minus(delay));
}
static Duration maxScalingWindow() {
return Duration.ofHours(48);
}
/** Returns the minimum measurements per node (average) we require to give autoscaling advice.*/
private int minimumMeasurementsPerNode(Duration scalingWindow) {
// Measurements are ideally taken every minute, but no guarantees
// (network, nodes may be down, collecting is single threaded and may take longer than 1 minute to complete).
// Since the metric window is 5 minutes, we won't really improve from measuring more often.
long minimumMeasurements = scalingWindow.toMinutes() / 5;
minimumMeasurements = Math.round(0.8 * minimumMeasurements); // Allow 20% metrics collection blackout
if (minimumMeasurements < 1) minimumMeasurements = 1;
return (int)minimumMeasurements;
}
public static class Advice {
private final boolean present;
private final Optional<ClusterResources> target;
private final AutoscalingStatus reason;
private Advice(Optional<ClusterResources> target, boolean present, AutoscalingStatus reason) {
this.target = target;
this.present = present;
this.reason = Objects.requireNonNull(reason);
}
/**
* Returns the autoscaling target that should be set by this advice.
* This is empty if the advice is to keep the current allocation.
*/
public Optional<ClusterResources> target() { return target; }
/** True if this does not provide any advice */
public boolean isEmpty() { return ! present; }
/** True if this provides advice (which may be to keep the current allocation) */
public boolean isPresent() { return present; }
/** The reason for this advice */
public AutoscalingStatus reason() { return reason; }
private static Advice none(Status status, String description) {
return new Advice(Optional.empty(), false, new AutoscalingStatus(status, description));
}
private static Advice dontScale(Status status, String description) {
return new Advice(Optional.empty(), true, new AutoscalingStatus(status, description));
}
private static Advice scaleTo(ClusterResources target) {
return new Advice(Optional.of(target), true,
new AutoscalingStatus(AutoscalingStatus.Status.rescaling,
"Rescaling initiated due to load changes"));
}
@Override
public String toString() {
return "autoscaling advice: " +
(present ? (target.isPresent() ? "Scale to " + target.get() : "Don't scale") : "None");
}
}
}
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