File-based discovery plugin (#20394)

This commit introduces a new plugin for file-based unicast hosts
discovery. This allows specifying the unicast hosts participating
in discovery through a `unicast_hosts.txt` file located in the
`config/discovery-file` directory. The plugin will use the hosts 
specified in this file as the set of hosts to ping during discovery.

The format of the `unicast_hosts.txt` file is to have one host/port
entry per line. The hosts file is read and parsed every time
discovery makes ping requests, thus a new version of the file that
is published to the config directory will automatically be picked
up.

Closes #20323

core/src/main/java/org/elasticsearch/discovery/zen/ping/unicast/UnicastZenPing.java

@@ -160,18 +160,10 @@ public class UnicastZenPing extends AbstractLifecycleComponent implements ZenPin
         }
 
         logger.debug("using initial hosts {}, with concurrent_connects [{}]", hosts, concurrentConnects);
-
         List<DiscoveryNode> configuredTargetNodes = new ArrayList<>();
-        for (String host : hosts) {
-            try {
-                TransportAddress[] addresses = transportService.addressesFromString(host, limitPortCounts);
-                for (TransportAddress address : addresses) {
-                    configuredTargetNodes.add(new DiscoveryNode(UNICAST_NODE_PREFIX + unicastNodeIdGenerator.incrementAndGet() + "#",
-                            address, emptyMap(), emptySet(), getVersion().minimumCompatibilityVersion()));
-                }
-            } catch (Exception e) {
-                throw new IllegalArgumentException("Failed to resolve address for [" + host + "]", e);
-            }
+        for (final String host : hosts) {
+            configuredTargetNodes.addAll(resolveDiscoveryNodes(host, limitPortCounts, transportService,
+                () -> UNICAST_NODE_PREFIX + unicastNodeIdGenerator.incrementAndGet() + "#"));
         }
         this.configuredTargetNodes = configuredTargetNodes.toArray(new DiscoveryNode[configuredTargetNodes.size()]);
 
@@ -183,6 +175,32 @@ public class UnicastZenPing extends AbstractLifecycleComponent implements ZenPin
                 threadFactory, threadPool.getThreadContext());
     }
 
+    /**
+     * Resolves a host to a list of discovery nodes.  The host is resolved into a transport
+     * address (or a collection of addresses if the number of ports is greater than one) and
+     * the transport addresses are used to created discovery nodes.
+     *
+     * @param host the host to resolve
+     * @param limitPortCounts the number of ports to resolve (should be 1 for non-local transport)
+     * @param transportService the transport service
+     * @param idGenerator the generator to supply unique ids for each discovery node
+     * @return a list of discovery nodes with resolved transport addresses
+     */
+    public static List<DiscoveryNode> resolveDiscoveryNodes(final String host, final int limitPortCounts,
+                                                            final TransportService transportService, final Supplier<String> idGenerator) {
+        List<DiscoveryNode> discoveryNodes = new ArrayList<>();
+        try {
+            TransportAddress[] addresses = transportService.addressesFromString(host, limitPortCounts);
+            for (TransportAddress address : addresses) {
+                discoveryNodes.add(new DiscoveryNode(idGenerator.get(), address, emptyMap(), emptySet(),
+                                                        Version.CURRENT.minimumCompatibilityVersion()));
+            }
+        } catch (Exception e) {
+            throw new IllegalArgumentException("Failed to resolve address for [" + host + "]", e);
+        }
+        return discoveryNodes;
+    }
+
     @Override
     protected void doStart() {
     }

dev-tools/smoke_test_rc.py

@@ -65,6 +65,7 @@ DEFAULT_PLUGINS = ["analysis-icu",
                    "analysis-stempel",
                    "discovery-azure-classic",
                    "discovery-ec2",
+                   "discovery-file",
                    "discovery-gce",
                    "ingest-attachment",
                    "ingest-geoip",

plugins/discovery-file/build.gradle

@@ -0,0 +1,29 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you 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.
+ */
+
+esplugin {
+    description 'Discovery file plugin enables unicast discovery from hosts stored in a file.'
+    classname 'org.elasticsearch.discovery.file.FileBasedDiscoveryPlugin'
+}
+
+bundlePlugin {
+    from('config/discovery-file') {
+        into 'config'
+    }
+}

plugins/discovery-file/config/discovery-file/unicast_hosts.txt

@@ -0,0 +1,20 @@
+# The unicast_hosts.txt file contains the list of unicast hosts to connect to
+# for pinging during the discovery process, when using the file-based discovery
+# mechanism.  This file should contain one entry per line, where an entry is a
+# host/port combination.  The host and port should be separated by a `:`.  If
+# the port is left off, a default port of 9300 is assumed.  For example, if the
+# cluster has three nodes that participate in the discovery process:
+# (1) 66.77.88.99 running on port 9300 (2) 66.77.88.100 running on port 9305
+# and (3) 66.77.88.99 running on port 10005, then this file should contain the
+# following text:
+#
+#10.10.10.5
+#10.10.10.6:9305
+#10.10.10.5:10005
+#
+# For IPv6 addresses, make sure to put a bracket around the host part of the address,
+# for example: [2001:cdba:0000:0000:0000:0000:3257:9652]:9301 (where 9301 is the port).
+#
+# NOTE: all lines starting with a `#` are comments, and comments must exist
+# on lines of their own (i.e. comments cannot begin in the middle of a line)
+#

plugins/discovery-file/src/main/java/org/elasticsearch/discovery/file/FileBasedDiscoveryPlugin.java

@@ -0,0 +1,51 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you 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.elasticsearch.discovery.file;
+
+import org.apache.logging.log4j.Logger;
+import org.elasticsearch.common.logging.Loggers;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.discovery.DiscoveryModule;
+import org.elasticsearch.env.Environment;
+import org.elasticsearch.plugins.DiscoveryPlugin;
+import org.elasticsearch.plugins.Plugin;
+
+/**
+ * Plugin for providing file-based unicast hosts discovery. The list of unicast hosts
+ * is obtained by reading the {@link FileBasedUnicastHostsProvider#UNICAST_HOSTS_FILE} in
+ * the {@link Environment#configFile()}/discovery-file directory.
+ */
+public class FileBasedDiscoveryPlugin extends Plugin implements DiscoveryPlugin {
+
+    private static final Logger logger = Loggers.getLogger(FileBasedDiscoveryPlugin.class);
+
+    private final Settings settings;
+
+    public FileBasedDiscoveryPlugin(Settings settings) {
+        this.settings = settings;
+        logger.trace("starting file-based discovery plugin...");
+    }
+
+    public void onModule(DiscoveryModule discoveryModule) {
+        logger.trace("registering file-based unicast hosts provider");
+        // using zen discovery for the discovery type and we're just adding a unicast host provider for it
+        discoveryModule.addUnicastHostProvider("zen", FileBasedUnicastHostsProvider.class);
+    }
+}

plugins/discovery-file/src/main/java/org/elasticsearch/discovery/file/FileBasedUnicastHostsProvider.java

@@ -0,0 +1,109 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you 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.elasticsearch.discovery.file;
+
+import org.apache.logging.log4j.message.ParameterizedMessage;
+import org.apache.logging.log4j.util.Supplier;
+import org.elasticsearch.cluster.node.DiscoveryNode;
+import org.elasticsearch.common.component.AbstractComponent;
+import org.elasticsearch.common.inject.Inject;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.discovery.zen.ping.unicast.UnicastHostsProvider;
+import org.elasticsearch.env.Environment;
+import org.elasticsearch.transport.TransportService;
+
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.NoSuchFileException;
+import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import static org.elasticsearch.discovery.zen.ping.unicast.UnicastZenPing.resolveDiscoveryNodes;
+
+/**
+ * An implementation of {@link UnicastHostsProvider} that reads hosts/ports
+ * from {@link #UNICAST_HOSTS_FILE}.
+ *
+ * Each unicast host/port that is part of the discovery process must be listed on
+ * a separate line.  If the port is left off an entry, a default port of 9300 is
+ * assumed.  An example unicast hosts file could read:
+ *
+ * 67.81.244.10
+ * 67.81.244.11:9305
+ * 67.81.244.15:9400
+ */
+public class FileBasedUnicastHostsProvider extends AbstractComponent implements UnicastHostsProvider {
+
+    static final String UNICAST_HOSTS_FILE = "unicast_hosts.txt";
+    static final String UNICAST_HOST_PREFIX = "#zen_file_unicast_host_";
+
+    private final TransportService transportService;
+
+    private final Path unicastHostsFilePath;
+
+    private final AtomicLong nodeIdGenerator = new AtomicLong(); // generates unique ids for the node
+
+    @Inject
+    public FileBasedUnicastHostsProvider(Settings settings, TransportService transportService) {
+        super(settings);
+        this.transportService = transportService;
+        this.unicastHostsFilePath = new Environment(settings).configFile().resolve("discovery-file").resolve(UNICAST_HOSTS_FILE);
+    }
+
+    @Override
+    public List<DiscoveryNode> buildDynamicNodes() {
+        List<String> hostsList;
+        try (Stream<String> lines = Files.lines(unicastHostsFilePath)) {
+            hostsList = lines.filter(line -> line.startsWith("#") == false) // lines starting with `#` are comments
+                             .collect(Collectors.toList());
+        } catch (FileNotFoundException | NoSuchFileException e) {
+            logger.warn((Supplier<?>) () -> new ParameterizedMessage("[discovery-file] Failed to find unicast hosts file [{}]",
+                                                                        unicastHostsFilePath), e);
+            hostsList = Collections.emptyList();
+        } catch (IOException e) {
+            logger.warn((Supplier<?>) () -> new ParameterizedMessage("[discovery-file] Error reading unicast hosts file [{}]",
+                                                                        unicastHostsFilePath), e);
+            hostsList = Collections.emptyList();
+        }
+
+        final List<DiscoveryNode> discoNodes = new ArrayList<>();
+        for (final String host : hostsList) {
+            try {
+                discoNodes.addAll(resolveDiscoveryNodes(host, 1, transportService,
+                    () -> UNICAST_HOST_PREFIX + nodeIdGenerator.incrementAndGet() + "#"));
+            } catch (IllegalArgumentException e) {
+                logger.warn((Supplier<?>) () -> new ParameterizedMessage("[discovery-file] Failed to parse transport address from [{}]",
+                                                                            host), e);
+                continue;
+            }
+        }
+
+        logger.debug("[discovery-file] Using dynamic discovery nodes {}", discoNodes);
+
+        return discoNodes;
+    }
+
+}

plugins/discovery-file/src/test/java/org/elasticsearch/discovery/file/FileBasedDiscoveryClientYamlTestSuiteIT.java

@@ -0,0 +1,43 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you 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.elasticsearch.discovery.file;
+
+import com.carrotsearch.randomizedtesting.annotations.Name;
+import com.carrotsearch.randomizedtesting.annotations.ParametersFactory;
+import org.elasticsearch.test.rest.yaml.ClientYamlTestCandidate;
+import org.elasticsearch.test.rest.yaml.ESClientYamlSuiteTestCase;
+import org.elasticsearch.test.rest.yaml.parser.ClientYamlTestParseException;
+
+import java.io.IOException;
+
+/**
+ * Integration tests to make sure the file-based discovery plugin works in a cluster.
+ */
+public class FileBasedDiscoveryClientYamlTestSuiteIT extends ESClientYamlSuiteTestCase {
+
+    public FileBasedDiscoveryClientYamlTestSuiteIT(@Name("yaml") ClientYamlTestCandidate testCandidate) {
+        super(testCandidate);
+    }
+
+    @ParametersFactory
+    public static Iterable<Object[]> parameters() throws IOException, ClientYamlTestParseException {
+        return ESClientYamlSuiteTestCase.createParameters(0, 1);
+    }
+}

plugins/discovery-file/src/test/java/org/elasticsearch/discovery/file/FileBasedUnicastHostsProviderTests.java

@@ -0,0 +1,139 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you 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.elasticsearch.discovery.file;
+
+import org.elasticsearch.cluster.node.DiscoveryNode;
+import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
+import org.elasticsearch.common.network.NetworkService;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.common.util.BigArrays;
+import org.elasticsearch.env.Environment;
+import org.elasticsearch.indices.breaker.NoneCircuitBreakerService;
+import org.elasticsearch.test.ESTestCase;
+import org.elasticsearch.test.transport.MockTransportService;
+import org.elasticsearch.threadpool.TestThreadPool;
+import org.elasticsearch.threadpool.ThreadPool;
+import org.elasticsearch.transport.MockTcpTransport;
+import org.junit.AfterClass;
+import org.junit.Before;
+import org.junit.BeforeClass;
+
+import java.io.BufferedWriter;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+
+import static org.elasticsearch.discovery.file.FileBasedUnicastHostsProvider.UNICAST_HOSTS_FILE;
+import static org.elasticsearch.discovery.file.FileBasedUnicastHostsProvider.UNICAST_HOST_PREFIX;
+
+/**
+ * Tests for {@link FileBasedUnicastHostsProvider}.
+ */
+public class FileBasedUnicastHostsProviderTests extends ESTestCase {
+
+    private static ThreadPool threadPool;
+    private MockTransportService transportService;
+
+    @BeforeClass
+    public static void createThreadPool() {
+        threadPool = new TestThreadPool(FileBasedUnicastHostsProviderTests.class.getName());
+    }
+
+    @AfterClass
+    public static void stopThreadPool() throws InterruptedException {
+        terminate(threadPool);
+    }
+
+    @Before
+    public void createTransportSvc() {
+        MockTcpTransport transport =
+            new MockTcpTransport(Settings.EMPTY,
+                                    threadPool,
+                                    BigArrays.NON_RECYCLING_INSTANCE,
+                                    new NoneCircuitBreakerService(),
+                                    new NamedWriteableRegistry(Collections.emptyList()),
+                                    new NetworkService(Settings.EMPTY, Collections.emptyList()));
+        transportService = new MockTransportService(Settings.EMPTY, transport, threadPool);
+    }
+
+    public void testBuildDynamicNodes() throws Exception {
+        final List<String> hostEntries = Arrays.asList("#comment, should be ignored", "192.168.0.1", "192.168.0.2:9305", "255.255.23.15");
+        final List<DiscoveryNode> nodes = setupAndRunHostProvider(hostEntries);
+        assertEquals(hostEntries.size() - 1, nodes.size()); // minus 1 because we are ignoring the first line that's a comment
+        assertEquals("192.168.0.1", nodes.get(0).getAddress().getHost());
+        assertEquals(9300, nodes.get(0).getAddress().getPort());
+        assertEquals(UNICAST_HOST_PREFIX + "1#", nodes.get(0).getId());
+        assertEquals("192.168.0.2", nodes.get(1).getAddress().getHost());
+        assertEquals(9305, nodes.get(1).getAddress().getPort());
+        assertEquals(UNICAST_HOST_PREFIX + "2#", nodes.get(1).getId());
+        assertEquals("255.255.23.15", nodes.get(2).getAddress().getHost());
+        assertEquals(9300, nodes.get(2).getAddress().getPort());
+        assertEquals(UNICAST_HOST_PREFIX + "3#", nodes.get(2).getId());
+    }
+
+    public void testEmptyUnicastHostsFile() throws Exception {
+        final List<String> hostEntries = Collections.emptyList();
+        final List<DiscoveryNode> nodes = setupAndRunHostProvider(hostEntries);
+        assertEquals(0, nodes.size());
+    }
+
+    public void testUnicastHostsDoesNotExist() throws Exception {
+        final Settings settings = Settings.builder()
+                                      .put(Environment.PATH_HOME_SETTING.getKey(), createTempDir())
+                                      .build();
+        final FileBasedUnicastHostsProvider provider = new FileBasedUnicastHostsProvider(settings, transportService);
+        final List<DiscoveryNode> nodes = provider.buildDynamicNodes();
+        assertEquals(0, nodes.size());
+    }
+
+    public void testInvalidHostEntries() throws Exception {
+        List<String> hostEntries = Arrays.asList("192.168.0.1:9300:9300");
+        List<DiscoveryNode> nodes = setupAndRunHostProvider(hostEntries);
+        assertEquals(0, nodes.size());
+    }
+
+    public void testSomeInvalidHostEntries() throws Exception {
+        List<String> hostEntries = Arrays.asList("192.168.0.1:9300:9300", "192.168.0.1:9301");
+        List<DiscoveryNode> nodes = setupAndRunHostProvider(hostEntries);
+        assertEquals(1, nodes.size()); // only one of the two is valid and will be used
+        assertEquals("192.168.0.1", nodes.get(0).getAddress().getHost());
+        assertEquals(9301, nodes.get(0).getAddress().getPort());
+    }
+
+    // sets up the config dir, writes to the unicast hosts file in the config dir,
+    // and then runs the file-based unicast host provider to get the list of discovery nodes
+    private List<DiscoveryNode> setupAndRunHostProvider(final List<String> hostEntries) throws IOException {
+        final Path homeDir = createTempDir();
+        final Settings settings = Settings.builder()
+                                      .put(Environment.PATH_HOME_SETTING.getKey(), homeDir)
+                                      .build();
+        final Path configDir = homeDir.resolve("config").resolve("discovery-file");
+        Files.createDirectories(configDir);
+        final Path unicastHostsPath = configDir.resolve(UNICAST_HOSTS_FILE);
+        try (BufferedWriter writer = Files.newBufferedWriter(unicastHostsPath)) {
+            writer.write(String.join("\n", hostEntries));
+        }
+
+        return new FileBasedUnicastHostsProvider(settings, transportService).buildDynamicNodes();
+    }
+}

plugins/discovery-file/src/test/resources/rest-api-spec/test/discovery_file/10_basic.yaml

@@ -0,0 +1,13 @@
+# Integration tests for file-based discovery
+#
+"Discovery File loaded":
+    - do:
+        cluster.state: {}
+
+    # Get master node id
+    - set: { master_node: master }
+
+    - do:
+        nodes.info: {}
+
+    - match:  { nodes.$master.plugins.0.name: discovery-file  }

qa/vagrant/src/test/resources/packaging/scripts/module_and_plugin_test_cases.bash

@@ -217,6 +217,10 @@ fi
     install_and_check_plugin discovery ec2 aws-java-sdk-core-*.jar
 }
 
+@test "[$GROUP] install discovery-file plugin" {
+    install_and_check_plugin discovery file
+}
+
 @test "[$GROUP] install ingest-attachment plugin" {
     # we specify the version on the poi-3.15-beta1.jar so that the test does
     # not spuriously pass if the jar is missing but the other poi jars
@@ -353,6 +357,10 @@ fi
     remove_plugin discovery-ec2
 }
 
+@test "[$GROUP] remove discovery-file plugin" {
+    remove_plugin discovery-file
+}
+
 @test "[$GROUP] remove ingest-attachment plugin" {
     remove_plugin ingest-attachment
 }

settings.gradle

@@ -38,6 +38,7 @@ List projects = [
   'plugins:analysis-stempel',
   'plugins:discovery-azure-classic',
   'plugins:discovery-ec2',
+  'plugins:discovery-file',
   'plugins:discovery-gce',
   'plugins:ingest-geoip',
   'plugins:ingest-attachment',