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// Copyright Vespa.ai. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
package com.yahoo.config.application.api;
import com.yahoo.config.provision.RegionName;
import java.time.Duration;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Optional;
import java.util.Set;
import java.util.stream.Collectors;
/**
* Defines the BCP structure for an instance in a deployment spec:
* A list of region groups where each group contains a set of regions
* which will handle the traffic of a member in the group when it becomes unreachable.
*
* This is used to make bcp-aware autoscaling decisions. If no explicit BCP spec
* is provided, it is assumed that a regions traffic will be divided equally over all
* the other regions when it becomes unreachable - i.e a single BCP group is implicitly
* defined having all defined production regions as members with fraction 1.0.
*
* It is assumed that the traffic of the unreachable region is distributed
* evenly to the other members of the group.
*
* A region can be a fractional member of a group, in which case it is assumed that
* region will only handle that fraction of its share of the unreachable regions traffic,
* and symmetrically that the other members of the group will only handle that fraction
* of the fraction regions traffic if it becomes unreachable.
*
* Each production region defined in the instance must have fractional memberships in groups that sums to exactly one.
*
* If a group has one member it will not set aside any capacity for BCP.
* If a group has more than two members, the system will attempt to provision capacity
* for BCP also when a region is unreachable. That is, if there are three member regions, A, B and C,
* each handling 100 qps, then they each aim to handle 150 in case one goes down. If C goes down,
* A and B will now handle 150 each, but will each aim to handle 300 each in case the other goes down.
*
* @author bratseth
*/
public class Bcp {
private static final Bcp empty = new Bcp(List.of(), Optional.empty());
private final Optional<Duration> defaultDeadline;
private final List<Group> groups;
public Bcp(List<Group> groups, Optional<Duration> defaultDeadline) {
totalMembershipSumsToOne(groups);
this.defaultDeadline = defaultDeadline;
this.groups = List.copyOf(groups);
}
public Optional<Duration> defaultDeadline() { return defaultDeadline; }
public List<Group> groups() { return groups; }
public Bcp withGroups(List<Group> groups) {
return new Bcp(groups, defaultDeadline);
}
/** Returns the set of regions declared in the groups of this. */
public Set<RegionName> regions() {
return groups.stream().flatMap(group -> group.members().stream()).map(member -> member.region()).collect(Collectors.toSet());
}
public boolean isEmpty() { return groups.isEmpty() && defaultDeadline.isEmpty(); }
/** Returns this bcp spec, or if it is empty, the given bcp spec. */
public Bcp orElse(Bcp other) {
return this.isEmpty() ? other : this;
}
private void totalMembershipSumsToOne(List<Group> groups) {
Map<RegionName, Double> totalMembership = new HashMap<>();
for (var group : groups) {
for (var member : group.members())
totalMembership.compute(member.region(), (__, fraction) -> fraction == null ? member.fraction()
: fraction + member.fraction());
}
for (var entry : totalMembership.entrySet()) {
if (entry.getValue() != 1.0)
throw new IllegalArgumentException("Illegal BCP spec: All regions must have total membership fractions summing to 1.0, but " +
entry.getKey() + " sums to " + entry.getValue());
}
}
public static Bcp empty() { return empty; }
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Bcp bcp = (Bcp) o;
return defaultDeadline.equals(bcp.defaultDeadline) && groups.equals(bcp.groups);
}
@Override
public int hashCode() {
return Objects.hash(defaultDeadline, groups);
}
@Override
public String toString() {
if (isEmpty()) return "empty BCP";
return "BCP of " +
( groups.isEmpty() ? "no groups" : groups ) +
(defaultDeadline.isEmpty() ? "" : ", deadline: " + defaultDeadline.get());
}
public static class Group {
private final List<RegionMember> members;
private final Set<RegionName> memberRegions;
private final Duration deadline;
public Group(List<RegionMember> members, Duration deadline) {
this.members = List.copyOf(members);
this.memberRegions = members.stream().map(member -> member.region()).collect(Collectors.toSet());
this.deadline = deadline;
}
public List<RegionMember> members() { return members; }
public Set<RegionName> memberRegions() { return memberRegions; }
/**
* Returns the max time until the other regions must be able to handle the additional traffic
* when a region becomes unreachable, which by default is Duration.ZERO.
*/
public Duration deadline() { return deadline; }
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Group group = (Group) o;
return members.equals(group.members) && memberRegions.equals(group.memberRegions) && deadline.equals(group.deadline);
}
@Override
public int hashCode() {
return Objects.hash(members, memberRegions, deadline);
}
@Override
public String toString() {
return "BCP group of " + members;
}
}
public record RegionMember(RegionName region, double fraction) {
public RegionMember {
if (fraction < 0 || fraction > 1)
throw new IllegalArgumentException("Fraction must be a number between 0.0 and 1.0, but got " + fraction);
}
}
}
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