allow ldap user search connection pool creation to be retried if it fails on startup

Today, if a LDAP server is down and the LDAP realm uses the user search mechanism this will prevent the
node from starting up. This is not ideal because users can still authenticate with another realm if it is
configured. This change tries to create the connection pool on initialization but if it fails, creation will retried
on each attempted authentication until the server is available again.

Closes elastic/elasticsearch#107

Original commit: elastic/x-pack-elasticsearch@f2ccf858ff

shield/src/main/java/org/elasticsearch/shield/authc/ldap/LdapUserSearchSessionFactory.java

@@ -8,6 +8,7 @@ package org.elasticsearch.shield.authc.ldap;
 import com.google.common.primitives.Ints;
 import com.unboundid.ldap.sdk.*;
 import org.elasticsearch.common.Strings;
+import org.elasticsearch.common.logging.ESLogger;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.unit.TimeValue;
 import org.elasticsearch.shield.ShieldSettingsFilter;
@@ -36,15 +37,17 @@ public class LdapUserSearchSessionFactory extends SessionFactory {
     static final TimeValue DEFAULT_HEALTH_CHECK_INTERVAL = TimeValue.timeValueSeconds(60L);
 
     private final GroupsResolver groupResolver;
-    private final LDAPConnectionPool connectionPool;
     private final String userSearchBaseDn;
     private final LdapSearchScope scope;
     private final String userAttribute;
     private final ServerSet serverSet;
+    private final Settings settings;
 
-    public LdapUserSearchSessionFactory(RealmConfig config, ClientSSLService sslService) throws IOException {
+    private LDAPConnectionPool connectionPool;
+
+    public LdapUserSearchSessionFactory(RealmConfig config, ClientSSLService sslService) {
         super(config);
-        Settings settings = config.settings();
+        settings = config.settings();
         userSearchBaseDn = settings.get("user_search.base_dn");
         if (userSearchBaseDn == null) {
             throw new IllegalArgumentException("user_search base_dn must be specified");
@@ -52,17 +55,29 @@ public class LdapUserSearchSessionFactory extends SessionFactory {
         scope = LdapSearchScope.resolve(settings.get("user_search.scope"), LdapSearchScope.SUB_TREE);
         userAttribute = settings.get("user_search.attribute", DEFAULT_USERNAME_ATTRIBUTE);
         serverSet = serverSet(settings, sslService);
-        connectionPool = connectionPool(config.settings(), serverSet, timeout);
+        connectionPool = createConnectionPool(settings, serverSet, timeout, logger);
         groupResolver = groupResolver(settings);
     }
 
+    private synchronized LDAPConnectionPool connectionPool() throws IOException {
+        if (connectionPool == null) {
+            connectionPool = createConnectionPool(settings, serverSet, timeout, logger);
+            // if it is still null throw an exception
+            if (connectionPool == null) {
+                throw new IOException("failed to create a connection pool as no LDAP servers are available");
+            }
+        }
+
+        return connectionPool;
+    }
+
     static void filterOutSensitiveSettings(String realmName, ShieldSettingsFilter filter) {
         filter.filterOut("shield.authc.realms." + realmName + ".bind_dn");
         filter.filterOut("shield.authc.realms." + realmName + ".bind_password");
         filter.filterOut("shield.authc.realms." + realmName + "." + HOSTNAME_VERIFICATION_SETTING);
     }
 
-    static LDAPConnectionPool connectionPool(Settings settings, ServerSet serverSet, TimeValue timeout) throws IOException {
+    static LDAPConnectionPool createConnectionPool(Settings settings, ServerSet serverSet, TimeValue timeout, ESLogger logger) {
         SimpleBindRequest bindRequest = bindRequest(settings);
         int initialSize = settings.getAsInt("user_search.pool.initial_size", DEFAULT_CONNECTION_POOL_INITIAL_SIZE);
         int size = settings.getAsInt("user_search.pool.size", DEFAULT_CONNECTION_POOL_SIZE);
@@ -85,8 +100,13 @@ public class LdapUserSearchSessionFactory extends SessionFactory {
             }
             return pool;
         } catch (LDAPException e) {
-            throw new IOException("unable to connect to any LDAP servers", e);
+            if (logger.isDebugEnabled()) {
+                logger.debug("unable to create connection pool", e);
+            } else {
+                logger.error("unable to create connection pool: {}", e.getMessage());
+            }
         }
+        return null;
     }
 
     static SimpleBindRequest bindRequest(Settings settings) {
@@ -126,6 +146,7 @@ public class LdapUserSearchSessionFactory extends SessionFactory {
     public LdapSession session(String user, SecuredString password) throws Exception {
         SearchRequest request = new SearchRequest(userSearchBaseDn, scope.scope(), createEqualityFilter(userAttribute, encodeValue(user)), Strings.EMPTY_ARRAY);
         request.setTimeLimitSeconds(Ints.checkedCast(timeout.seconds()));
+        LDAPConnectionPool connectionPool = connectionPool();
         try {
             SearchResultEntry entry = searchForEntry(connectionPool, request, logger);
             if (entry == null) {
@@ -160,7 +181,9 @@ public class LdapUserSearchSessionFactory extends SessionFactory {
      * This method is used to cleanup the connections for tests
      */
     void shutdown() {
-        connectionPool.close();
+        if (connectionPool != null) {
+            connectionPool.close();
+        }
     }
 
     static GroupsResolver groupResolver(Settings settings) {

shield/src/test/java/org/elasticsearch/shield/authc/ldap/LdapUserSearchSessionFactoryTests.java

@@ -5,12 +5,18 @@
  */
 package org.elasticsearch.shield.authc.ldap;
 
+import com.carrotsearch.randomizedtesting.ThreadFilter;
+import com.carrotsearch.randomizedtesting.annotations.ThreadLeakFilters;
 import com.unboundid.ldap.sdk.*;
 import org.elasticsearch.ElasticsearchSecurityException;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.unit.TimeValue;
 import org.elasticsearch.env.Environment;
+import org.elasticsearch.license.plugin.LicensePlugin;
+import org.elasticsearch.node.Node;
+import org.elasticsearch.node.NodeBuilder;
+import org.elasticsearch.shield.ShieldPlugin;
 import org.elasticsearch.shield.authc.RealmConfig;
 import org.elasticsearch.shield.authc.activedirectory.ActiveDirectorySessionFactoryTests;
 import org.elasticsearch.shield.authc.ldap.support.LdapSearchScope;
@@ -19,6 +25,7 @@ import org.elasticsearch.shield.authc.ldap.support.LdapTest;
 import org.elasticsearch.shield.authc.support.SecuredString;
 import org.elasticsearch.shield.authc.support.SecuredStringTests;
 import org.elasticsearch.shield.ssl.ClientSSLService;
+import org.elasticsearch.shield.support.NoOpLogger;
 import org.elasticsearch.test.junit.annotations.Network;
 import org.junit.Before;
 import org.junit.Test;
@@ -27,11 +34,17 @@ import java.nio.file.Path;
 import java.text.MessageFormat;
 import java.util.List;
 import java.util.Locale;
+import java.util.Map;
 
 import static org.elasticsearch.common.settings.Settings.settingsBuilder;
 import static org.elasticsearch.test.ShieldTestsUtils.assertAuthenticationException;
 import static org.hamcrest.Matchers.*;
 
+// thread leak filter for UnboundID's background connect threads. The background connect threads do not always respect the
+// timeout and linger. Will be fixed in a new version of the library, see http://sourceforge.net/p/ldap-sdk/discussion/1001257/thread/154e3b71/
+@ThreadLeakFilters(filters = {
+        LdapUserSearchSessionFactoryTests.BackgroundConnectThreadLeakFilter.class
+})
 public class LdapUserSearchSessionFactoryTests extends LdapTest {
 
     private ClientSSLService clientSSLService;
@@ -306,7 +319,7 @@ public class LdapUserSearchSessionFactoryTests extends LdapTest {
                 .put("bind_password", "pass")
                 .build(), globalSettings);
 
-        LDAPConnectionPool connectionPool = LdapUserSearchSessionFactory.connectionPool(config.settings(), new SingleServerSet("localhost", ldapServer.getListenPort()), TimeValue.timeValueSeconds(5));
+        LDAPConnectionPool connectionPool = LdapUserSearchSessionFactory.createConnectionPool(config.settings(), new SingleServerSet("localhost", ldapServer.getListenPort()), TimeValue.timeValueSeconds(5), NoOpLogger.INSTANCE);
         try {
             assertThat(connectionPool.getCurrentAvailableConnections(), is(LdapUserSearchSessionFactory.DEFAULT_CONNECTION_POOL_INITIAL_SIZE));
             assertThat(connectionPool.getMaximumAvailableConnections(), is(LdapUserSearchSessionFactory.DEFAULT_CONNECTION_POOL_SIZE));
@@ -333,7 +346,7 @@ public class LdapUserSearchSessionFactoryTests extends LdapTest {
                 .put("user_search.pool.health_check.enabled", false)
                 .build(), globalSettings);
 
-        LDAPConnectionPool connectionPool = LdapUserSearchSessionFactory.connectionPool(config.settings(), new SingleServerSet("localhost", ldapServer.getListenPort()), TimeValue.timeValueSeconds(5));
+        LDAPConnectionPool connectionPool = LdapUserSearchSessionFactory.createConnectionPool(config.settings(), new SingleServerSet("localhost", ldapServer.getListenPort()), TimeValue.timeValueSeconds(5), NoOpLogger.INSTANCE);
         try {
             assertThat(connectionPool.getCurrentAvailableConnections(), is(10));
             assertThat(connectionPool.getMaximumAvailableConnections(), is(12));
@@ -377,4 +390,41 @@ public class LdapUserSearchSessionFactoryTests extends LdapTest {
         SimpleBindRequest simpleBindRequest = (SimpleBindRequest) request;
         assertThat(simpleBindRequest.getBindDN(), is("cn=ironman"));
     }
+
+    @Test
+    public void testThatLDAPServerConnectErrorDoesNotPreventNodeFromStarting() {
+        String groupSearchBase = "DC=ad,DC=test,DC=elasticsearch,DC=com";
+        String userSearchBase = "CN=Users,DC=ad,DC=test,DC=elasticsearch,DC=com";
+        Settings ldapSettings = settingsBuilder()
+                .put(LdapTest.buildLdapSettings("ldaps://elastic.co:636", Strings.EMPTY_ARRAY, groupSearchBase, LdapSearchScope.SUB_TREE))
+                .put("user_search.base_dn", userSearchBase)
+                .put("bind_dn", "ironman@ad.test.elasticsearch.com")
+                .put("bind_password", ActiveDirectorySessionFactoryTests.PASSWORD)
+                .put("user_search.attribute", "cn")
+                .put("timeout.tcp_connect", "500ms")
+                .put("type", "ldap")
+                .build();
+
+        Settings.Builder builder = settingsBuilder();
+        for (Map.Entry<String, String> entry : ldapSettings.getAsMap().entrySet()) {
+            builder.put("shield.authc.realms.ldap1." + entry.getKey(), entry.getValue());
+        }
+        builder.put("path.home", createTempDir());
+        builder.putArray("plugin.types", ShieldPlugin.class.getName(), LicensePlugin.class.getName());
+
+        try (Node node = NodeBuilder.nodeBuilder().loadConfigSettings(false).settings(builder.build()).build()) {
+            node.start();
+        }
+    }
+
+    public static class BackgroundConnectThreadLeakFilter implements ThreadFilter {
+
+        @Override
+        public boolean reject(Thread thread) {
+            if (thread.getName().startsWith("Background connect thread for elastic.co")) {
+                return true;
+            }
+            return false;
+        }
+    }
 }