Talk of MasterElection nacos RaftCore

sequence

In this paper, we look nacos RaftCore of MasterElection

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);
    }

	//......
}
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• RaftCore init method registered MasterElection by GlobalExecutor.registerMasterElection (new 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);
    }

    //......
}
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• registerMasterElection method of scheduling a runnable milliseconds every TICK_PERIOD_MS

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);

                            return 0;
                        }
                    });
                } catch (Exception e) {
                    Loggers.RAFT.warn("error while sending vote to server: {}", server);
                }
            }
        }
    }
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• MasterElection method implements Runnable whose run method is ready in less than peers and local.leaderDueMs minus TICK_PERIOD_MS equal to 0 will proceed to the election; it first resetLeaderDue and resetHeartbeatDue, and then perform sendVote method; sendVote method first reset peers, incremental localPeer the term, and set voteFor for yourself, and then update the state as RaftPeer.State.CANDIDATE, finally traversing peers.allServersWithoutMySelf (), the asynchronous post their vote information to other peer; if the other peer returns successfully execute peers.decideLeader (peer ) returns 1, otherwise it returns 0

summary

RaftCore init method by GlobalExecutor.registerMasterElection (new MasterElection ()) registered MasterElection; registerMasterElection method TICK_PERIOD_MS milliseconds every scheduling time; MasterElection implements Runnable method, which methods are run in ready peers and subtracting TICK_PERIOD_MS less local.leaderDueMs 0 when the elections will start; it was first resetLeaderDue and resetHeartbeatDue, then execute sendVote method

doc

• RaftCore