Talk about Nacos RaftCore’s MasterElection

sequence

This article mainly studies the MasterElection of NacOS RaftCore

RaftCore

Nacos – 1.1.3 / naming/SRC/main/Java/com/alibaba/nacos/naming/consistency/persistent/raft/RaftCore Java

@Component
public class RaftCore {
	
	//......

    @PostConstruct
    public void init() throws Exception {

        Loggers.RAFT.info("initializing Raft sub-system");

        executor.submit(notifier);

        long start = System.currentTimeMillis();

        raftStore.loadDatums(notifier, datums);

        setTerm(NumberUtils.toLong(raftStore.loadMeta().getProperty("term"), 0L));

        Loggers.RAFT.info("cache loaded, datum count: {}, current term: {}", datums.size(), peers.getTerm());

        while (true) {
            if (notifier.tasks.size() <= 0) {
                break;
            }
            Thread.sleep(1000L);
        }

        initialized = true;

        Loggers.RAFT.info("finish to load data from disk, cost: {} ms.", (System.currentTimeMillis() - start));

        GlobalExecutor.registerMasterElection(new MasterElection());
        GlobalExecutor.registerHeartbeat(new HeartBeat());

        Loggers.RAFT.info("timer started: leader timeout ms: {}, heart-beat timeout ms: {}", GlobalExecutor.LEADER_TIMEOUT_MS, GlobalExecutor.HEARTBEAT_INTERVAL_MS); } / /... }Copy the code

• RaftCore init method through GlobalExecutor. RegisterMasterElection (new MasterElection ()) registered MasterElection

GlobalExecutor

Nacos – 1.1.3 / naming/SRC/main/Java/com/alibaba/nacos/naming/misc/GlobalExecutor Java

public class GlobalExecutor { //...... public static final long TICK_PERIOD_MS = TimeUnit.MILLISECONDS.toMillis(500L); public static void registerMasterElection(Runnable runnable) { executorService.scheduleAtFixedRate(runnable, 0, TICK_PERIOD_MS, TimeUnit.MILLISECONDS); } / /... }Copy the code

• The registerMasterElection method dispatches runnable every TICK_PERIOD_MS millisecond

MasterElection

Nacos – 1.1.3 / naming/SRC/main/Java/com/alibaba/nacos/naming/consistency/persistent/raft/RaftCore Java

    public class MasterElection implements Runnable {
        @Override
        public void run() {
            try {

                if(! peers.isReady()) {return;
                }

                RaftPeer local = peers.local();
                local.leaderDueMs -= GlobalExecutor.TICK_PERIOD_MS;

                if (local.leaderDueMs > 0) {
                    return;
                }

                // reset timeout
                local.resetLeaderDue();
                local.resetHeartbeatDue();

                sendVote();
            } catch (Exception e) {
                Loggers.RAFT.warn("[RAFT] error while master election {}", e);
            }

        }

        public void sendVote() {

            RaftPeer local = peers.get(NetUtils.localServer());
            Loggers.RAFT.info("leader timeout, start voting,leader: {}, term: {}",
                JSON.toJSONString(getLeader()), local.term);

            peers.reset();

            local.term.incrementAndGet();
            local.voteFor = local.ip;
            local.state = RaftPeer.State.CANDIDATE;

            Map<String, String> params = new HashMap<>(1);
            params.put("vote", JSON.toJSONString(local));
            for (final String server : peers.allServersWithoutMySelf()) {
                final String url = buildURL(server, API_VOTE);
                try {
                    HttpClient.asyncHttpPost(url, null, params, new AsyncCompletionHandler<Integer>() {
                        @Override
                        public Integer onCompleted(Response response) throws Exception {
                            if(response.getStatusCode() ! = HttpURLConnection.HTTP_OK) { Loggers.RAFT.error("NACOS-RAFT vote failed: {}, url: {}", response.getResponseBody(), url);
                                return 1;
                            }

                            RaftPeer peer = JSON.parseObject(response.getResponseBody(), RaftPeer.class);

                            Loggers.RAFT.info("received approve from peer: {}", JSON.toJSONString(peer));

                            peers.decideLeader(peer);

                            return0; }}); } catch (Exception e) { Loggers.RAFT.warn("error while sending vote to server: {}", server); }}}}Copy the code

• MasterElection implements the Runnable method, whose run method starts the election when peers are all ready and local.leaderDueMs minus TICK_PERIOD_MS is less than or equal to 0. It first resetLeaderDue and resetHeartbeatDue and then executes the sendVote method; The sendVote method first resets peers, increments term of localPeer, sets voteFor to itself, and then updates state to raftpeer-.state.candidate, The traversal peers. AllServersWithoutMySelf (), will own asynchronous post that information to the other peer; Execute peers. DecideLeader (peer) if the other peers return success and return 1, otherwise return 0

summary

RaftCore init method through GlobalExecutor. RegisterMasterElection (new MasterElection ()) registered MasterElection; The registerMasterElection method is scheduled every TICK_PERIOD_MS ms; MasterElection implements the Runnable method, whose run method starts the election when peers are all ready and local.leaderDueMs minus TICK_PERIOD_MS is less than or equal to 0. It first resetLeaderDue and resetHeartbeatDue and then executes the sendVote method

doc

• RaftCore