Give useful error message if log config is missing

Today when starting Elasticsearch without a Log4j 2 configuration file,
we end up throwing an array index out of bounds exception. This is
because we are passing no configuration files to Log4j. Instead, we
should throw a useful error message to the user. This commit modifies
the Log4j configuration setup to throw a user exception if no Log4j
configuration files are present in the config directory.

Relates #20493

core/src/main/java/org/elasticsearch/bootstrap/Bootstrap.java

@@ -28,6 +28,7 @@ import org.apache.lucene.util.StringHelper;
 import org.elasticsearch.ElasticsearchException;
 import org.elasticsearch.Version;
 import org.elasticsearch.cli.Terminal;
+import org.elasticsearch.cli.UserException;
 import org.elasticsearch.common.PidFile;
 import org.elasticsearch.common.SuppressForbidden;
 import org.elasticsearch.common.inject.CreationException;
@@ -233,7 +234,7 @@ final class Bootstrap {
             final boolean foreground,
             final Path pidFile,
             final boolean quiet,
-            final Map<String, String> esSettings) throws BootstrapException, NodeValidationException {
+            final Map<String, String> esSettings) throws BootstrapException, NodeValidationException, UserException {
         // Set the system property before anything has a chance to trigger its use
         initLoggerPrefix();
 

core/src/main/java/org/elasticsearch/bootstrap/Elasticsearch.java

@@ -107,7 +107,7 @@ class Elasticsearch extends SettingCommand {
     }
 
     void init(final boolean daemonize, final Path pidFile, final boolean quiet, final Map<String, String> esSettings)
-            throws  NodeValidationException {
+        throws NodeValidationException, UserException {
         try {
             Bootstrap.init(!daemonize, pidFile, quiet, esSettings);
         } catch (BootstrapException | RuntimeException e) {

core/src/main/java/org/elasticsearch/common/logging/LogConfigurator.java

@@ -30,6 +30,8 @@ import org.apache.logging.log4j.core.config.builder.impl.BuiltConfiguration;
 import org.apache.logging.log4j.core.config.composite.CompositeConfiguration;
 import org.apache.logging.log4j.core.config.properties.PropertiesConfiguration;
 import org.apache.logging.log4j.core.config.properties.PropertiesConfigurationFactory;
+import org.elasticsearch.cli.ExitCodes;
+import org.elasticsearch.cli.UserException;
 import org.elasticsearch.cluster.ClusterName;
 import org.elasticsearch.common.SuppressForbidden;
 import org.elasticsearch.common.settings.Settings;
@@ -50,7 +52,7 @@ import java.util.Set;
 
 public class LogConfigurator {
 
-    public static void configure(final Environment environment, final boolean resolveConfig) throws IOException {
+    public static void configure(final Environment environment, final boolean resolveConfig) throws IOException, UserException {
         final Settings settings = environment.settings();
 
         setLogConfigurationSystemProperty(environment, settings);
@@ -75,6 +77,13 @@ public class LogConfigurator {
                     return FileVisitResult.CONTINUE;
                 }
             });
+
+            if (configurations.isEmpty()) {
+                throw new UserException(
+                    ExitCodes.CONFIG,
+                    "no log4j2.properties found; tried [" + environment.configFile() + "] and its subdirectories");
+            }
+
             context.start(new CompositeConfiguration(configurations));
         }
 

qa/evil-tests/src/test/java/org/elasticsearch/common/logging/EvilLoggerConfigurationTests.java

@@ -27,6 +27,7 @@ import org.apache.logging.log4j.core.LoggerContext;
 import org.apache.logging.log4j.core.config.Configuration;
 import org.apache.logging.log4j.core.config.Configurator;
 import org.apache.logging.log4j.core.config.LoggerConfig;
+import org.elasticsearch.cli.UserException;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.env.Environment;
 import org.elasticsearch.test.ESTestCase;
@@ -34,7 +35,9 @@ import org.elasticsearch.test.ESTestCase;
 import java.io.IOException;
 import java.nio.file.Path;
 
+import static org.hamcrest.CoreMatchers.containsString;
 import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.Matchers.hasToString;
 import static org.hamcrest.Matchers.notNullValue;
 
 public class EvilLoggerConfigurationTests extends ESTestCase {
@@ -85,7 +88,7 @@ public class EvilLoggerConfigurationTests extends ESTestCase {
         }
     }
 
-    public void testDefaults() throws IOException {
+    public void testDefaults() throws IOException, UserException {
         final Path configDir = getDataPath("config");
         final String level = randomFrom(Level.TRACE, Level.DEBUG, Level.INFO, Level.WARN, Level.ERROR).toString();
         final Settings settings = Settings.builder()
@@ -137,4 +140,15 @@ public class EvilLoggerConfigurationTests extends ESTestCase {
         assertThat(ESLoggerFactory.getLogger("x.y").getLevel(), equalTo(level));
     }
 
+    public void testMissingConfigFile() {
+        final Path configDir = getDataPath("does_not_exist");
+        final Settings settings = Settings.builder()
+            .put(Environment.PATH_CONF_SETTING.getKey(), configDir.toAbsolutePath())
+            .put(Environment.PATH_HOME_SETTING.getKey(), createTempDir().toString())
+            .build();
+        final Environment environment = new Environment(settings);
+        UserException e = expectThrows(UserException.class, () -> LogConfigurator.configure(environment, true));
+        assertThat(e, hasToString(containsString("no log4j2.properties found; tried")));
+    }
+
 }

qa/evil-tests/src/test/java/org/elasticsearch/common/logging/EvilLoggerTests.java

@@ -28,6 +28,7 @@ import org.apache.logging.log4j.core.appender.ConsoleAppender;
 import org.apache.logging.log4j.core.appender.CountingNoOpAppender;
 import org.apache.logging.log4j.core.config.Configurator;
 import org.apache.logging.log4j.message.ParameterizedMessage;
+import org.elasticsearch.cli.UserException;
 import org.elasticsearch.common.io.PathUtils;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.env.Environment;
@@ -59,7 +60,7 @@ public class EvilLoggerTests extends ESTestCase {
         super.tearDown();
     }
 
-    public void testLocationInfoTest() throws IOException {
+    public void testLocationInfoTest() throws IOException, UserException {
         setupLogging("location_info");
 
         final Logger testLogger = ESLoggerFactory.getLogger("test");
@@ -81,7 +82,7 @@ public class EvilLoggerTests extends ESTestCase {
         assertLogLine(events.get(4), Level.TRACE, location, "This is a trace message");
     }
 
-    public void testDeprecationLogger() throws IOException {
+    public void testDeprecationLogger() throws IOException, UserException {
         setupLogging("deprecation");
 
         final DeprecationLogger deprecationLogger = new DeprecationLogger(ESLoggerFactory.getLogger("deprecation"));
@@ -97,7 +98,7 @@ public class EvilLoggerTests extends ESTestCase {
             "This is a deprecation message");
     }
 
-    public void testFindAppender() throws IOException {
+    public void testFindAppender() throws IOException, UserException {
         setupLogging("find_appender");
 
         final Logger hasConsoleAppender = ESLoggerFactory.getLogger("has_console_appender");
@@ -111,7 +112,7 @@ public class EvilLoggerTests extends ESTestCase {
         assertThat(countingNoOpAppender.getName(), equalTo("counting_no_op"));
     }
 
-    public void testPrefixLogger() throws IOException, IllegalAccessException {
+    public void testPrefixLogger() throws IOException, IllegalAccessException, UserException {
         setupLogging("prefix");
 
         final String prefix = randomBoolean() ? null : randomAsciiOfLength(16);
@@ -179,7 +180,7 @@ public class EvilLoggerTests extends ESTestCase {
         }
     }
 
-    private void setupLogging(final String config) throws IOException {
+    private void setupLogging(final String config) throws IOException, UserException {
         final Path configDir = getDataPath(config);
         // need to set custom path.conf so we can use a custom log4j2.properties file for the test
         final Settings settings = Settings.builder()