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// Copyright Verizon Media. 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.ClusterSpec;
import com.yahoo.config.provision.NodeResources;
import com.yahoo.vespa.hosted.provision.Node;
import com.yahoo.vespa.hosted.provision.NodeRepository;
import com.yahoo.vespa.hosted.provision.applications.Cluster;
import java.time.Duration;
import java.time.Instant;
import java.util.List;
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 factor is worth a reallocation? */
private static final double costDifferenceWorthReallocation = 0.1;
/** What difference factor for a resource is worth a reallocation? */
private static final double resourceDifferenceWorthReallocation = 0.1;
private final MetricsDb metricsDb;
private final NodeRepository nodeRepository;
private final AllocationOptimizer allocationOptimizer;
public Autoscaler(MetricsDb metricsDb, NodeRepository nodeRepository) {
this.metricsDb = metricsDb;
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(Cluster cluster, List<Node> clusterNodes) {
return autoscale(cluster, clusterNodes, Limits.empty(), cluster.exclusive());
}
/**
* 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(Cluster cluster, List<Node> clusterNodes) {
if (cluster.minResources().equals(cluster.maxResources())) return Advice.none("Autoscaling is disabled"); // Shortcut
return autoscale(cluster, clusterNodes, Limits.of(cluster), cluster.exclusive());
}
private Advice autoscale(Cluster cluster, List<Node> clusterNodes, Limits limits, boolean exclusive) {
ClusterSpec clusterSpec = clusterNodes.get(0).allocation().get().membership().cluster();
if ( ! stable(clusterNodes, nodeRepository))
return Advice.none("Cluster change in progress");
AllocatableClusterResources currentAllocation =
new AllocatableClusterResources(clusterNodes, nodeRepository, cluster.exclusive());
ClusterTimeseries clusterTimeseries = new ClusterTimeseries(cluster, clusterNodes, metricsDb, nodeRepository);
int measurementsPerNode = clusterTimeseries.measurementsPerNode();
if (measurementsPerNode < minimumMeasurementsPerNode(clusterSpec))
return Advice.none("Collecting more data before making new scaling decisions" +
": Has " + measurementsPerNode + " data points per node" +
" (all: " + clusterTimeseries.measurementCount +
", without stale: " + clusterTimeseries.measurementCountWithoutStale +
", without out of service: " + clusterTimeseries.measurementCountWithoutStaleOutOfService +
", without unstable: " + clusterTimeseries.measurementCountWithoutStaleOutOfServiceUnstable + ")");
int nodesMeasured = clusterTimeseries.nodesMeasured();
if (nodesMeasured != clusterNodes.size())
return Advice.none("Collecting more data before making new scaling decisions" +
": Has measurements from " + nodesMeasured + " but need from " + clusterNodes.size());
double cpuLoad = clusterTimeseries.averageLoad(Resource.cpu);
double memoryLoad = clusterTimeseries.averageLoad(Resource.memory);
double diskLoad = clusterTimeseries.averageLoad(Resource.disk);
var target = ResourceTarget.idealLoad(cpuLoad, memoryLoad, diskLoad, currentAllocation);
Optional<AllocatableClusterResources> bestAllocation =
allocationOptimizer.findBestAllocation(target, currentAllocation, limits, exclusive);
if (bestAllocation.isEmpty())
return Advice.dontScale("No allocation changes are possible within configured limits");
if (similar(bestAllocation.get(), currentAllocation))
return Advice.dontScale("Cluster is ideally scaled (within configured limits)");
if (isDownscaling(bestAllocation.get(), currentAllocation) && recentlyScaled(cluster, clusterNodes))
return Advice.dontScale("Waiting a while before scaling down");
return Advice.scaleTo(bestAllocation.get().toAdvertisedClusterResources());
}
/** Returns true if both total real resources and total cost are similar */
private boolean similar(AllocatableClusterResources a, AllocatableClusterResources b) {
return similar(a.cost(), b.cost(), costDifferenceWorthReallocation) &&
similar(a.realResources().vcpu() * a.nodes(),
b.realResources().vcpu() * b.nodes(), resourceDifferenceWorthReallocation) &&
similar(a.realResources().memoryGb() * a.nodes(),
b.realResources().memoryGb() * b.nodes(), resourceDifferenceWorthReallocation) &&
similar(a.realResources().diskGb() * a.nodes(),
b.realResources().diskGb() * b.nodes(), resourceDifferenceWorthReallocation);
}
private 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.toAdvertisedClusterResources().totalResources();
NodeResources currentTotal = current.toAdvertisedClusterResources().totalResources();
return ! targetTotal.justNumbers().satisfies(currentTotal.justNumbers());
}
private boolean recentlyScaled(Cluster cluster, List<Node> clusterNodes) {
Duration downscalingDelay = downscalingDelay(clusterNodes.get(0).allocation().get().membership().cluster());
return cluster.lastScalingEvent().map(event -> event.at()).orElse(Instant.MIN)
.isAfter(nodeRepository.clock().instant().minus(downscalingDelay));
}
/** The duration of the window we need to consider to make a scaling decision. See also minimumMeasurementsPerNode */
static Duration scalingWindow(ClusterSpec cluster) {
if (cluster.isStateful()) return Duration.ofHours(12);
return Duration.ofMinutes(30);
}
static Duration maxScalingWindow() {
return Duration.ofHours(12);
}
/** Measurements are currently taken once a minute. See also scalingWindow */
static int minimumMeasurementsPerNode(ClusterSpec cluster) {
if (cluster.isStateful()) return 60;
return 7;
}
/**
* We should wait a while before scaling down after a scaling event as a peak in usage
* indicates more peaks may arrive in the near future.
*/
static Duration downscalingDelay(ClusterSpec cluster) {
if (cluster.isStateful()) return Duration.ofHours(12);
return Duration.ofHours(1);
}
public static boolean stable(List<Node> nodes, NodeRepository nodeRepository) {
// The cluster is processing recent changes
if (nodes.stream().anyMatch(node -> node.status().wantToRetire() ||
node.allocation().get().membership().retired() ||
node.allocation().get().isRemovable()))
return false;
// A deployment is ongoing
if (nodeRepository.getNodes(nodes.get(0).allocation().get().owner(), Node.State.reserved).size() > 0)
return false;
return true;
}
public static class Advice {
private final boolean present;
private final Optional<ClusterResources> target;
private final String reason;
private Advice(Optional<ClusterResources> target, boolean present, String 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 String reason() { return reason; }
private static Advice none(String reason) { return new Advice(Optional.empty(), false, reason); }
private static Advice dontScale(String reason) { return new Advice(Optional.empty(), true, reason); }
private static Advice scaleTo(ClusterResources target) {
return new Advice(Optional.of(target), true, "Scaling 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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