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本文主要研究一下elasticsearch的SeedHostsProvider

SeedHostsProvider

elasticsearch-7.0.0/server/src/main/java/org/elasticsearch/discovery/SeedHostsProvider.java

/**
 * A pluggable provider of the list of seed hosts to use for discovery.
 */
public interface SeedHostsProvider {

    /**
     * Returns a list of seed hosts to use for discovery. Called repeatedly while discovery is active (i.e. while there is no master)
     * so that this list may be dynamic.
     */
    List<TransportAddress> getSeedAddresses(HostsResolver hostsResolver);

    /**
     * Helper object that allows to resolve a list of hosts to a list of transport addresses.
     * Each host is resolved into a transport address (or a collection of addresses if the
     * number of ports is greater than one)
     */
    interface HostsResolver {
        List<TransportAddress> resolveHosts(List<String> hosts, int limitPortCounts);
    }
}

• SeedHostsProvider接口定义了getSeedAddresses方法，该方法参数类型为HostsResolver；HostsResolver接口定义了resolveHosts方法；它有几个实现类，分别是SettingsBasedSeedHostsProvider、FileBasedSeedHostsProvider、GceSeedHostsProvider、AwsEc2SeedHostsProvider、AzureSeedHostsProvider

SettingsBasedSeedHostsProvider

elasticsearch-7.0.0/server/src/main/java/org/elasticsearch/discovery/SettingsBasedSeedHostsProvider.java

public class SettingsBasedSeedHostsProvider implements SeedHostsProvider {

    private static final Logger logger = LogManager.getLogger(SettingsBasedSeedHostsProvider.class);

    public static final Setting<List<String>> LEGACY_DISCOVERY_ZEN_PING_UNICAST_HOSTS_SETTING =
        Setting.listSetting("discovery.zen.ping.unicast.hosts", emptyList(), Function.identity(), Property.NodeScope, Property.Deprecated);

    public static final Setting<List<String>> DISCOVERY_SEED_HOSTS_SETTING =
        Setting.listSetting("discovery.seed_hosts", emptyList(), Function.identity(), Property.NodeScope);

    // these limits are per-address
    private static final int LIMIT_FOREIGN_PORTS_COUNT = 1;
    private static final int LIMIT_LOCAL_PORTS_COUNT = 5;

    private final List<String> configuredHosts;
    private final int limitPortCounts;

    public SettingsBasedSeedHostsProvider(Settings settings, TransportService transportService) {
        if (LEGACY_DISCOVERY_ZEN_PING_UNICAST_HOSTS_SETTING.exists(settings)) {
            if (DISCOVERY_SEED_HOSTS_SETTING.exists(settings)) {
                throw new IllegalArgumentException("it is forbidden to set both ["
                    + DISCOVERY_SEED_HOSTS_SETTING.getKey() + "] and ["
                    + LEGACY_DISCOVERY_ZEN_PING_UNICAST_HOSTS_SETTING.getKey() + "]");
            }
            configuredHosts = LEGACY_DISCOVERY_ZEN_PING_UNICAST_HOSTS_SETTING.get(settings);
            // we only limit to 1 address, makes no sense to ping 100 ports
            limitPortCounts = LIMIT_FOREIGN_PORTS_COUNT;
        } else if (DISCOVERY_SEED_HOSTS_SETTING.exists(settings)) {
            configuredHosts = DISCOVERY_SEED_HOSTS_SETTING.get(settings);
            // we only limit to 1 address, makes no sense to ping 100 ports
            limitPortCounts = LIMIT_FOREIGN_PORTS_COUNT;
        } else {
            // if unicast hosts are not specified, fill with simple defaults on the local machine
            configuredHosts = transportService.getLocalAddresses();
            limitPortCounts = LIMIT_LOCAL_PORTS_COUNT;
        }

        logger.debug("using initial hosts {}", configuredHosts);
    }

    @Override
    public List<TransportAddress> getSeedAddresses(HostsResolver hostsResolver) {
        return hostsResolver.resolveHosts(configuredHosts, limitPortCounts);
    }
}

• SettingsBasedSeedHostsProvider主要是读取discovery.seed_hosts或discovery.zen.ping.unicast.hosts配置

FileBasedSeedHostsProvider

elasticsearch-7.0.0/server/src/main/java/org/elasticsearch/discovery/FileBasedSeedHostsProvider.java

public class FileBasedSeedHostsProvider implements SeedHostsProvider {

    private static final Logger logger = LogManager.getLogger(FileBasedSeedHostsProvider.class);

    public static final String UNICAST_HOSTS_FILE = "unicast_hosts.txt";

    private final Path unicastHostsFilePath;

    public FileBasedSeedHostsProvider(Path configFile) {
        this.unicastHostsFilePath = configFile.resolve(UNICAST_HOSTS_FILE);
    }

    private List<String> getHostsList() {
        if (Files.exists(unicastHostsFilePath)) {
            try (Stream<String> lines = Files.lines(unicastHostsFilePath)) {
                return lines.filter(line -> line.startsWith("#") == false) // lines starting with `#` are comments
                    .collect(Collectors.toList());
            } catch (IOException e) {
                logger.warn(() -> new ParameterizedMessage("failed to read file [{}]", unicastHostsFilePath), e);
                return Collections.emptyList();
            }
        }

        logger.warn("expected, but did not find, a dynamic hosts list at [{}]", unicastHostsFilePath);

        return Collections.emptyList();
    }

    @Override
    public List<TransportAddress> getSeedAddresses(HostsResolver hostsResolver) {
        final List<TransportAddress> transportAddresses = hostsResolver.resolveHosts(getHostsList(), 1);
        logger.debug("seed addresses: {}", transportAddresses);
        return transportAddresses;
    }
}

• FileBasedSeedHostsProvider主要是从指定位置读取unicast_hosts.txt文件解析hostsList

SeedHostsProvider.HostsResolver

UnicastZenPing.createHostsResolver

elasticsearch-7.0.0/server/src/main/java/org/elasticsearch/discovery/zen/UnicastZenPing.java

    private SeedHostsProvider.HostsResolver createHostsResolver() {
        return (hosts, limitPortCounts) -> SeedHostsResolver.resolveHostsLists(unicastZenPingExecutorService, logger, hosts,
            limitPortCounts, transportService, resolveTimeout);
    }

• UnicastZenPing的createHostsResolver方法创建了一个匿名的SeedHostsProvider.HostsResolver类，其实现是委托为SeedHostsResolver.resolveHostsLists方法

SeedHostsResolver

elasticsearch-7.0.0/server/src/main/java/org/elasticsearch/discovery/SeedHostsResolver.java

public class SeedHostsResolver extends AbstractLifecycleComponent implements ConfiguredHostsResolver {

    //......

    public static List<TransportAddress> resolveHostsLists(
        final ExecutorService executorService,
        final Logger logger,
        final List<String> hosts,
        final int limitPortCounts,
        final TransportService transportService,
        final TimeValue resolveTimeout) {
        Objects.requireNonNull(executorService);
        Objects.requireNonNull(logger);
        Objects.requireNonNull(hosts);
        Objects.requireNonNull(transportService);
        Objects.requireNonNull(resolveTimeout);
        if (resolveTimeout.nanos() < 0) {
            throw new IllegalArgumentException("resolve timeout must be non-negative but was [" + resolveTimeout + "]");
        }
        // create tasks to submit to the executor service; we will wait up to resolveTimeout for these tasks to complete
        final List<Callable<TransportAddress[]>> callables =
            hosts
                .stream()
                .map(hn -> (Callable<TransportAddress[]>) () -> transportService.addressesFromString(hn, limitPortCounts))
                .collect(Collectors.toList());
        final List<Future<TransportAddress[]>> futures;
        try {
            futures = executorService.invokeAll(callables, resolveTimeout.nanos(), TimeUnit.NANOSECONDS);
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
            return Collections.emptyList();
        }
        final List<TransportAddress> transportAddresses = new ArrayList<>();
        final Set<TransportAddress> localAddresses = new HashSet<>();
        localAddresses.add(transportService.boundAddress().publishAddress());
        localAddresses.addAll(Arrays.asList(transportService.boundAddress().boundAddresses()));
        // ExecutorService#invokeAll guarantees that the futures are returned in the iteration order of the tasks so we can associate the
        // hostname with the corresponding task by iterating together
        final Iterator<String> it = hosts.iterator();
        for (final Future<TransportAddress[]> future : futures) {
            final String hostname = it.next();
            if (!future.isCancelled()) {
                assert future.isDone();
                try {
                    final TransportAddress[] addresses = future.get();
                    logger.trace("resolved host [{}] to {}", hostname, addresses);
                    for (int addressId = 0; addressId < addresses.length; addressId++) {
                        final TransportAddress address = addresses[addressId];
                        // no point in pinging ourselves
                        if (localAddresses.contains(address) == false) {
                            transportAddresses.add(address);
                        }
                    }
                } catch (final ExecutionException e) {
                    assert e.getCause() != null;
                    final String message = "failed to resolve host [" + hostname + "]";
                    logger.warn(message, e.getCause());
                } catch (InterruptedException e) {
                    Thread.currentThread().interrupt();
                    // ignore
                }
            } else {
                logger.warn("timed out after [{}] resolving host [{}]", resolveTimeout, hostname);
            }
        }
        return Collections.unmodifiableList(transportAddresses);
    }

    //......
}

• SeedHostsResolver的resolveHostsLists静态方法主要是利用多线程并行执行transportService.addressesFromString方法

小结

• SeedHostsProvider接口定义了getSeedAddresses方法，该方法参数类型为HostsResolver；HostsResolver接口定义了resolveHosts方法；它有几个实现类，分别是SettingsBasedSeedHostsProvider、FileBasedSeedHostsProvider、GceSeedHostsProvider、AwsEc2SeedHostsProvider、AzureSeedHostsProvider
• SettingsBasedSeedHostsProvider主要是读取discovery.seed_hosts或discovery.zen.ping.unicast.hosts配置；FileBasedSeedHostsProvider主要是从指定位置读取unicast_hosts.txt文件解析hostsList
• UnicastZenPing的createHostsResolver方法创建了一个匿名的SeedHostsProvider.HostsResolver类，其实现是委托为SeedHostsResolver.resolveHostsLists方法；SeedHostsResolver的resolveHostsLists静态方法主要是利用多线程并行执行transportService.addressesFromString方法

doc

• SeedHostsProvider