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Easy Redis Java client and Real-Time Data Platform. Valkey compatible. Sync/Async/RxJava3/Reactive API. Client side caching. Over 50 Redis based Java objects and services: JCache API, Apache Tomcat, Hibernate, Spring, Set, Multimap, SortedSet, Map, List, Queue, Deque, Semaphore, Lock, AtomicLong, Map Reduce, Bloom filter, Scheduler, RPC
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/**
 * Copyright (c) 2013-2021 Nikita Koksharov
 *
 * 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.
 */
package org.redisson.connection;

import io.netty.resolver.AddressResolver;
import io.netty.resolver.AddressResolverGroup;
import io.netty.util.concurrent.Future;
import io.netty.util.concurrent.FutureListener;
import io.netty.util.concurrent.ScheduledFuture;
import org.redisson.client.RedisClient;
import org.redisson.connection.ClientConnectionsEntry.FreezeReason;
import org.redisson.misc.AsyncCountDownLatch;
import org.redisson.misc.RedisURI;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.net.InetSocketAddress;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.TimeUnit;

/**
 * DNS changes monitor.
 * 
 * @author Nikita Koksharov
 *
 */
public class DNSMonitor {
    
    private static final Logger log = LoggerFactory.getLogger(DNSMonitor.class);

    private final AddressResolver resolver;
    private final ConnectionManager connectionManager;
    private final Map masters = new HashMap<>();
    private final Map slaves = new HashMap<>();
    
    private ScheduledFuture dnsMonitorFuture;
    private long dnsMonitoringInterval;

    public DNSMonitor(ConnectionManager connectionManager, RedisClient masterHost, Collection slaveHosts, long dnsMonitoringInterval, AddressResolverGroup resolverGroup) {
        this.resolver = resolverGroup.getResolver(connectionManager.getGroup().next());
        
        masterHost.resolveAddr().join();
        masters.put(masterHost.getConfig().getAddress(), masterHost.getAddr());
        
        for (RedisURI host : slaveHosts) {
            Future resolveFuture = resolver.resolve(InetSocketAddress.createUnresolved(host.getHost(), host.getPort()));
            resolveFuture.syncUninterruptibly();
            slaves.put(host, resolveFuture.getNow());
        }
        this.connectionManager = connectionManager;
        this.dnsMonitoringInterval = dnsMonitoringInterval;
    }
    
    public void start() {
        monitorDnsChange();
        log.debug("DNS monitoring enabled; Current masters: {}, slaves: {}", masters, slaves);
    }
    
    public void stop() {
        if (dnsMonitorFuture != null) {
            dnsMonitorFuture.cancel(true);
        }
    }
    
    private void monitorDnsChange() {
        dnsMonitorFuture = connectionManager.getGroup().schedule(new Runnable() {
            @Override
            public void run() {
                if (connectionManager.isShuttingDown()) {
                    return;
                }

                AsyncCountDownLatch latch = new AsyncCountDownLatch();
                latch.latch(() -> {
                    monitorDnsChange();
                }, masters.size() + slaves.size());
                monitorMasters(latch);
                monitorSlaves(latch);
            }

        }, dnsMonitoringInterval, TimeUnit.MILLISECONDS);
    }

    private void monitorMasters(AsyncCountDownLatch latch) {
        for (Entry entry : masters.entrySet()) {
            log.debug("Request sent to resolve ip address for master host: {}", entry.getKey().getHost());

            Future resolveFuture = resolver.resolve(InetSocketAddress.createUnresolved(entry.getKey().getHost(), entry.getKey().getPort()));
            resolveFuture.addListener((FutureListener) future -> {
                if (!future.isSuccess()) {
                    log.error("Unable to resolve " + entry.getKey().getHost(), future.cause());
                    latch.countDown();
                    return;
                }

                log.debug("Resolved ip: {} for master host: {}", future.getNow().getAddress(), entry.getKey().getHost());

                InetSocketAddress currentMasterAddr = entry.getValue();
                InetSocketAddress newMasterAddr = future.getNow();
                if (!newMasterAddr.getAddress().equals(currentMasterAddr.getAddress())) {
                    log.info("Detected DNS change. Master {} has changed ip from {} to {}",
                            entry.getKey(), currentMasterAddr.getAddress().getHostAddress(),
                            newMasterAddr.getAddress().getHostAddress());

                    MasterSlaveEntry masterSlaveEntry = connectionManager.getEntry(currentMasterAddr);
                    if (masterSlaveEntry == null) {
                        log.error("Unable to find entry for current master {}", currentMasterAddr);
                        latch.countDown();
                        return;
                    }

                    CompletableFuture changeFuture = masterSlaveEntry.changeMaster(newMasterAddr, entry.getKey());
                    changeFuture.whenComplete((r, e) -> {
                        latch.countDown();

                        if (e == null) {
                            masters.put(entry.getKey(), newMasterAddr);
                        }
                    });
                } else {
                    latch.countDown();
                }
            });
        }
    }

    private void monitorSlaves(AsyncCountDownLatch latch) {
        for (Entry entry : slaves.entrySet()) {
            log.debug("Request sent to resolve ip address for slave host: {}", entry.getKey().getHost());

            Future resolveFuture = resolver.resolve(InetSocketAddress.createUnresolved(entry.getKey().getHost(), entry.getKey().getPort()));
            resolveFuture.addListener((FutureListener) future -> {
                if (!future.isSuccess()) {
                    log.error("Unable to resolve " + entry.getKey().getHost(), future.cause());
                    latch.countDown();
                    return;
                }

                log.debug("Resolved ip: {} for slave host: {}", future.getNow().getAddress(), entry.getKey().getHost());

                InetSocketAddress currentSlaveAddr = entry.getValue();
                InetSocketAddress newSlaveAddr = future.getNow();
                if (!newSlaveAddr.getAddress().equals(currentSlaveAddr.getAddress())) {
                    log.info("Detected DNS change. Slave {} has changed ip from {} to {}",
                            entry.getKey().getHost(), currentSlaveAddr.getAddress().getHostAddress(), newSlaveAddr.getAddress().getHostAddress());
                    boolean slaveFound = false;
                    for (MasterSlaveEntry masterSlaveEntry : connectionManager.getEntrySet()) {
                        if (!masterSlaveEntry.hasSlave(currentSlaveAddr)) {
                            continue;
                        }

                        slaveFound = true;
                        if (masterSlaveEntry.hasSlave(newSlaveAddr)) {
                            masterSlaveEntry.slaveUp(newSlaveAddr, FreezeReason.MANAGER);
                            masterSlaveEntry.slaveDown(currentSlaveAddr, FreezeReason.MANAGER);
                            slaves.put(entry.getKey(), newSlaveAddr);
                            latch.countDown();
                        } else {
                            CompletableFuture addFuture = masterSlaveEntry.addSlave(newSlaveAddr, entry.getKey());
                            addFuture.whenComplete((res, e) -> {
                                latch.countDown();

                                if (e != null) {
                                    log.error("Can't add slave: " + newSlaveAddr, e);
                                    return;
                                }

                                masterSlaveEntry.slaveDown(currentSlaveAddr, FreezeReason.MANAGER);
                                slaves.put(entry.getKey(), newSlaveAddr);
                            });
                        }
                        break;
                    }
                    if (!slaveFound) {
                        latch.countDown();
                    }
                } else {
                    latch.countDown();
                }
            });
        }
    }

    
}