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/*
* ============LICENSE_START=======================================================
* feature-server-pool
* ================================================================================
* Copyright (C) 2020 AT&T Intellectual Property. All rights reserved.
* ================================================================================
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
* ============LICENSE_END=========================================================
*/
package org.onap.policy.drools.serverpool;
import static org.onap.policy.drools.serverpool.ServerPoolProperties.DEFAULT_LEADER_STABLE_IDLE_CYCLES;
import static org.onap.policy.drools.serverpool.ServerPoolProperties.DEFAULT_LEADER_STABLE_VOTING_CYCLES;
import static org.onap.policy.drools.serverpool.ServerPoolProperties.LEADER_STABLE_IDLE_CYCLES;
import static org.onap.policy.drools.serverpool.ServerPoolProperties.LEADER_STABLE_VOTING_CYCLES;
import static org.onap.policy.drools.serverpool.ServerPoolProperties.getProperty;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.PrintStream;
import java.nio.charset.StandardCharsets;
import java.util.Base64;
import java.util.HashSet;
import java.util.TreeMap;
import java.util.TreeSet;
import java.util.UUID;
import javax.ws.rs.client.Entity;
import javax.ws.rs.core.MediaType;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* This class handles the election of the lead server. The lead server
* handles bucket assignments, and also is the server running the
* 'Discovery' procedure long-term (other servers do run the procedure
* until a leader is elected).
* Note that everything in this class is run under the 'MainLoop' thread,
* with the exception of the invocation and first two statements of the
* 'voteData' method.
*/
class Leader {
private static Logger logger = LoggerFactory.getLogger(Leader.class);
// Listener class to handle state changes that may lead to a new election
private static EventHandler eventHandler = new EventHandler();
static {
Events.register(eventHandler);
}
// Server currently in the leader roll
private static Server leader = null;
// Vote state machine -- it is null, unless a vote is in progress
private static VoteCycle voteCycle = null;
private static UUID emptyUUID = new UUID(0L, 0L);
/*==================================================*/
/* Some properties extracted at initialization time */
/*==================================================*/
// how many cycles of stability before voting starts
private static int stableIdleCycles;
// how may cycles of stability before declaring a winner
private static int stableVotingCycles;
/**
* Hide implicit public constructor.
*/
private Leader() {
// everything here is static -- no instances of this class are created
}
/**
* Invoked at startup, or after some events -- immediately start a new vote.
*/
static void startup() {
// fetch some static properties
stableIdleCycles = getProperty(LEADER_STABLE_IDLE_CYCLES,
DEFAULT_LEADER_STABLE_IDLE_CYCLES);
stableVotingCycles = getProperty(LEADER_STABLE_VOTING_CYCLES,
DEFAULT_LEADER_STABLE_VOTING_CYCLES);
startVoting();
}
/**
* start, or restart voting.
*/
private static void startVoting() {
if (voteCycle == null) {
voteCycle = new VoteCycle();
MainLoop.addBackgroundWork(voteCycle);
} else {
voteCycle.serverChanged();
}
}
/**
* Return the current leader.
*
* @return the current leader ('null' if none has been selected)
*/
public static Server getLeader() {
return leader;
}
/**
* Handle an incoming /vote REST message.
*
* @param data base64-encoded data, containing vote data
*/
static void voteData(byte[] data) {
// decode base64 data
final byte[] packet = Base64.getDecoder().decode(data);
MainLoop.queueWork(() -> {
// This runs within the 'MainLoop' thread --
// create the 'VoteCycle' state machine, if needed
if (voteCycle == null) {
voteCycle = new VoteCycle();
MainLoop.addBackgroundWork(voteCycle);
}
try {
// pass data to 'VoteCycle' state machine
voteCycle.packetReceived(packet);
} catch (IOException e) {
logger.error("Exception in 'Leader.voteData", e);
}
});
}
/* ============================================================ */
/**
* There is a single instance of this class (Leader.eventHandler), which
* is registered to listen for notifications of state transitions. Note
* that all of these methods are running within the 'MainLoop' thread.
*/
private static class EventHandler implements Events {
/**
* {@inheritDoc}
*/
@Override
public void newServer(Server server) {
// a new server has joined -- start/restart the VoteCycle state machine
startVoting();
}
/**
* {@inheritDoc}
*/
@Override
public void serverFailed(Server server) {
if (server == leader) {
// the lead server has failed --
// start/restart the VoteCycle state machine
leader = null;
startVoting();
// send out a notification that the lead server has failed
for (Events listener : Events.getListeners()) {
listener.leaderFailed(server);
}
} else if (voteCycle != null) {
// a vote is in progress -- restart the state machine
// (don't do anything if there is no vote in progress)
voteCycle.serverChanged();
}
}
}
/* ============================================================ */
/**
* This is the 'VoteCycle' state machine -- it runs as background work
* on the 'MainLoop' thread, and goes away when a leader is elected.
*/
private static class VoteCycle implements Runnable {
enum State {
// server just started up -- 5 second grace period
STARTUP,
// voting in progress -- changes have occurred in the last cycle
VOTING,
}
// maps UUID voted for into the associated data
private final TreeMap<UUID, VoteData> uuidToVoteData =
new TreeMap<>(Util.uuidComparator);
// maps voter UUID into the associated data
private final TreeMap<UUID, VoterData> uuidToVoterData =
new TreeMap<>(Util.uuidComparator);
// sorted list of 'VoteData' (most preferable to least)
private final TreeSet<VoteData> voteData = new TreeSet<>();
// data to send out next cycle
private final HashSet<VoterData> updatedVotes = new HashSet<>();
private State state = State.STARTUP;
private int cycleCount = stableIdleCycles;
/**
* Constructor - if there is no leader, or this server is the leader,
* start the 'Discovery' thread.
*/
VoteCycle() {
if (leader == null || leader == Server.getThisServer()) {
Discovery.startDiscovery();
}
}
/**
* A state change has occurred that invalidates any vote in progress --
* restart the VoteCycle state machine.
*/
void serverChanged() {
// clear all of the tables
uuidToVoteData.clear();
uuidToVoterData.clear();
voteData.clear();
updatedVotes.clear();
// wait for things to stabilize before continuing
state = State.STARTUP;
cycleCount = stableIdleCycles;
}
/**
* {@inheritDoc}
*/
@Override
public void run() {
switch (state) {
case STARTUP:
startupState();
break;
case VOTING:
votingState();
break;
default:
logger.error("Unknown state: {}", state);
break;
}
}
private void startupState() {
// 5-second grace period -- wait for things to stablize before
// starting the vote
cycleCount -= 1;
if (cycleCount <= 0) {
logger.info("VoteCycle: {} seconds have passed",
stableIdleCycles);
updateMyVote();
sendOutUpdates();
state = State.VOTING;
cycleCount = stableVotingCycles;
}
}
private void votingState() {
// need to be in the VOTING state without any vote changes
// for 5 seconds -- once this happens, the leader is chosen
if (sendOutUpdates()) {
// changes have occurred -- set the grace period to 5 seconds
cycleCount = stableVotingCycles;
return;
}
cycleCount -= 1;
if (cycleCount > 0) {
return;
}
// 5 second grace period has passed -- the leader is one with
// the most votes, which is the first entry in 'voteData'
Server oldLeader = leader;
leader = Server.getServer(voteData.first().uuid);
if (leader != oldLeader) {
// the leader has changed -- send out notifications
for (Events listener : Events.getListeners()) {
listener.newLeader(leader);
}
} else {
// the election is over, and the leader has been confirmed
for (Events listener : Events.getListeners()) {
listener.leaderConfirmed(leader);
}
}
if (leader == Server.getThisServer()) {
// this is the lead server --
// make sure the 'Discovery' threads are running
Discovery.startDiscovery();
} else {
// this is not the lead server -- stop 'Discovery' threads
Discovery.stopDiscovery();
}
// we are done with voting -- clean up, and report results
MainLoop.removeBackgroundWork(this);
voteCycle = null;
ByteArrayOutputStream bos = new ByteArrayOutputStream();
PrintStream out = new PrintStream(bos);
out.println("Voting results:");
// x(36) xxxxx x(36)
// UUID Votes Voter
String format = "%-36s %5s %-36s\n";
out.format(format, "UUID", "Votes", "Voter(s)");
out.format(format, "----", "-----", "--------");
for (VoteData vote : voteData) {
if (vote.voters.isEmpty()) {
out.format(format, vote.uuid, 0, "");
continue;
}
boolean headerNeeded = true;
for (VoterData voter : vote.voters) {
if (headerNeeded) {
out.format(format, vote.uuid,
vote.voters.size(), voter.uuid);
headerNeeded = false;
} else {
out.format(format, "", "", voter.uuid);
}
}
}
logger.info(bos.toString());
}
/**
* Process an incoming /vote REST message.
*
* @param packet vote data, containing one or more votes
*/
private void packetReceived(byte[] packet) throws IOException {
DataInputStream dis =
new DataInputStream(new ByteArrayInputStream(packet));
while (dis.available() != 0) {
// message is a series of:
// 16-bytes voter UUID
// 16-bytes vote UUID
// 8-bytes timestamp
long tmp = dis.readLong(); // most significant bits
UUID voter = new UUID(tmp, dis.readLong());
tmp = dis.readLong();
UUID vote = new UUID(tmp, dis.readLong());
long timestamp = dis.readLong();
// process the single vote
processVote(voter, vote, timestamp);
}
}
/**
* Process a single incoming vote.
*
* @param UUID voter the UUID of the Server making this vote
* @param UUID vote the UUID of the Server that 'voter' voted for
* @param timestamp the time when the vote was made
*/
private void processVote(UUID voter, UUID vote, long timestamp) {
// fetch old data for this voter
VoterData voterData = uuidToVoterData.computeIfAbsent(voter,
key -> new VoterData(voter, timestamp));
if (timestamp >= voterData.timestamp) {
// this is a new vote for this voter -- update the timestamp
voterData.timestamp = timestamp;
} else {
// already processed vote, and it may even be obsolete
return;
}
// fetch the old vote, if any, for this voter
VoteData oldVoteData = voterData.vote;
VoteData newVoteData = null;
if (vote != null) {
newVoteData = uuidToVoteData.computeIfAbsent(vote, key -> new VoteData(vote));
}
if (oldVoteData != newVoteData) {
// the vote has changed -- update the 'voterData' entry,
// and include this in the next set of outgoing messages
logger.info("{} voting for {}", voter, vote);
voterData.vote = newVoteData;
updatedVotes.add(voterData);
if (oldVoteData != null) {
// remove the old vote data
voteData.remove(oldVoteData);
oldVoteData.voters.remove(voterData);
if (oldVoteData.voters.isEmpty()) {
// no voters left -- remove the entry
uuidToVoteData.remove(oldVoteData.uuid);
} else {
// reinsert in a new position
voteData.add(oldVoteData);
}
}
if (newVoteData != null) {
// update the new vote data
voteData.remove(newVoteData);
newVoteData.voters.add(voterData);
voteData.add(newVoteData);
}
}
}
/**
* If any updates have occurred, send then out to all servers on
* the "notify list".
*
* @return 'true' if one or more votes have changed, 'false' if not
*/
private boolean sendOutUpdates() {
try {
if (updatedVotes.isEmpty()) {
// no changes to send out
return false;
}
// possibly change vote based on current information
updateMyVote();
// generate message to send out
ByteArrayOutputStream bos = new ByteArrayOutputStream();
DataOutputStream dos = new DataOutputStream(bos);
// go through all of the updated votes
for (VoterData voterData : updatedVotes) {
// voter UUID
dos.writeLong(voterData.uuid.getMostSignificantBits());
dos.writeLong(voterData.uuid.getLeastSignificantBits());
// vote UUID
UUID vote =
(voterData.vote == null ? emptyUUID : voterData.vote.uuid);
dos.writeLong(vote.getMostSignificantBits());
dos.writeLong(vote.getLeastSignificantBits());
// timestamp
dos.writeLong(voterData.timestamp);
}
updatedVotes.clear();
// create an 'Entity' that can be sent out to all hosts
Entity<String> entity = Entity.entity(
new String(Base64.getEncoder().encode(bos.toByteArray()), StandardCharsets.UTF_8),
MediaType.APPLICATION_OCTET_STREAM_TYPE);
// send out to all servers on the notify list
for (Server server : Server.getNotifyList()) {
server.post("vote", entity);
}
return true;
} catch (IOException e) {
logger.error("Exception in VoteCycle.sendOutUpdates", e);
return false;
}
}
/**
* (Possibly) change this servers vote, based upon votes of other voters.
*/
private void updateMyVote() {
UUID myVote = null;
if (uuidToVoterData.size() * 2 < Server.getServerCount()) {
// fewer than half of the nodes have voted
if (leader != null) {
// choose the current leader
myVote = leader.getUuid();
} else {
// choose the first entry in the servers list
myVote = Server.getFirstServer().getUuid();
}
} else {
// choose the first entry we know about
for (VoteData vote : voteData) {
if (Server.getServer(vote.uuid) != null) {
myVote = vote.uuid;
break;
}
}
}
if (myVote != null) {
// update the vote for this host, and include it in the list
processVote(Server.getThisServer().getUuid(), myVote,
System.currentTimeMillis());
}
}
}
/* ============================================================ */
/**
* This class corresponds to a single vote recipient --
* the Server being voted for.
*/
private static class VoteData implements Comparable<VoteData> {
// uuid voted for
private UUID uuid;
// the set of all voters that voted for this server
private HashSet<VoterData> voters = new HashSet<>();
/**
* Constructor -- set the UUID.
*/
VoteData(UUID uuid) {
this.uuid = uuid;
}
/*================================*/
/* Comparable<VoteData> interface */
/*================================*/
/**
* {@inheritDoc}
*/
@Override
public int compareTo(VoteData other) {
// favor highest vote count
// in case of a tie, compare UUIDs (favor smallest)
int rval = other.voters.size() - voters.size();
if (rval == 0) {
// vote counts equal -- favor the smaller UUID
rval = Util.uuidComparator.compare(uuid, other.uuid);
}
return rval;
}
}
/* ============================================================ */
/**
* This class corresponds to the vote of a single server.
*/
private static class VoterData {
// voter UUID
private UUID uuid;
// most recently cast vote from this voter
private VoteData vote = null;
// time when the vote was cast
private long timestamp = 0;
/**
* Constructor - store the UUID and timestamp.
*/
private VoterData(UUID uuid, long timestamp) {
this.uuid = uuid;
this.timestamp = timestamp;
}
}
}
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