Implement auto-config

pom.xml

@@ -30,7 +30,7 @@
 
         <jdk.version>1.8</jdk.version>
 
-        <hazelcast.version>4.0.2</hazelcast.version>
+        <hazelcast.version>4.1-SNAPSHOT</hazelcast.version>
 
         <junit.version>4.13</junit.version>
         <mockito.version>1.10.19</mockito.version>

src/main/java/com/hazelcast/azure/AzureDiscoveryStrategyFactory.java

@@ -16,11 +16,18 @@
 package com.hazelcast.azure;
 
 import com.hazelcast.config.properties.PropertyDefinition;
+import com.hazelcast.internal.nio.IOUtil;
 import com.hazelcast.logging.ILogger;
+import com.hazelcast.logging.Logger;
 import com.hazelcast.spi.discovery.DiscoveryNode;
 import com.hazelcast.spi.discovery.DiscoveryStrategy;
 import com.hazelcast.spi.discovery.DiscoveryStrategyFactory;
 
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
@@ -31,6 +38,8 @@
  */
 public class AzureDiscoveryStrategyFactory implements DiscoveryStrategyFactory {
 
+    private static final ILogger LOGGER = Logger.getLogger(AzureDiscoveryStrategyFactory.class);
+
     @Override
     public Class<? extends DiscoveryStrategy> getDiscoveryStrategyType() {
         return AzureDiscoveryStrategy.class;
@@ -50,4 +59,56 @@ public Collection<PropertyDefinition> getConfigurationProperties() {
         }
         return result;
     }
+
+    /**
+     * Checks if Hazelcast is running on Azure.
+     * <p>
+     * To check if Hazelcast is running on Azure, we first check whether "internal.cloudapp.net" is present in the file
+     * "/etc/resolv.conf". Such an approach is not officially documented but seems like a good enough heuristic to detect an
+     * Azure Compute VM Instance. Since it's not the official method, we still need to make an API call to a local, non-routable
+     * address http://169.254.169.254/metadata/instance.
+     *
+     * @return true if running on Azure Instance
+     * @see https://docs.microsoft.com/en-us/azure/virtual-machines/linux/instance-metadata-service#metadata-apis
+     */
+    @Override
+    public boolean isAutoDetectionApplicable() {
+        return azureDnsServerConfigured() && azureInstanceMetadataAvailable();
+    }
+
+    private static boolean azureDnsServerConfigured() {
+        return readFileContents("/etc/resolv.conf").contains("internal.cloudapp.net");
+    }
+
+    static String readFileContents(String fileName) {
+        InputStream is = null;
+        try {
+            File file = new File(fileName);
+            byte[] data = new byte[(int) file.length()];
+            is = new FileInputStream(file);
+            is.read(data);
+            return new String(data, StandardCharsets.UTF_8);
+        } catch (IOException e) {
+            throw new RuntimeException("Could not get " + fileName, e);
+        } finally {
+            IOUtil.closeResource(is);
+        }
+    }
+
+    private static boolean azureInstanceMetadataAvailable() {
+        return isEndpointAvailable("http://169.254.169.254/metadata/instance?api-version=2020-06-01");
+    }
+
+
+    static boolean isEndpointAvailable(String url) {
+        return !RestClient.create(url)
+                .withHeader("Metadata", "True")
+                .get()
+                .isEmpty();
+    }
+
+    @Override
+    public DiscoveryStrategyLevel discoveryStrategyLevel() {
+        return DiscoveryStrategyLevel.CLOUD_VM;
+    }
 }

src/test/java/com/hazelcast/azure/AzureDiscoveryStrategyFactoryTest.java

@@ -15,20 +15,37 @@
 
 package com.hazelcast.azure;
 
+import com.github.tomakehurst.wiremock.junit.WireMockRule;
 import com.hazelcast.config.Config;
 import com.hazelcast.config.DiscoveryConfig;
 import com.hazelcast.config.XmlConfigBuilder;
+import com.hazelcast.internal.nio.IOUtil;
 import com.hazelcast.spi.discovery.DiscoveryStrategy;
 import com.hazelcast.spi.discovery.impl.DefaultDiscoveryService;
 import com.hazelcast.spi.discovery.integration.DiscoveryServiceSettings;
+import org.junit.Rule;
 import org.junit.Test;
 
+import java.io.BufferedWriter;
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
 import java.io.InputStream;
+import java.io.OutputStreamWriter;
+import java.nio.charset.StandardCharsets;
 import java.util.Iterator;
 
+import static com.github.tomakehurst.wiremock.client.WireMock.aResponse;
+import static com.github.tomakehurst.wiremock.client.WireMock.get;
+import static com.github.tomakehurst.wiremock.client.WireMock.stubFor;
+import static com.github.tomakehurst.wiremock.client.WireMock.urlEqualTo;
+import static com.github.tomakehurst.wiremock.core.WireMockConfiguration.wireMockConfig;
+import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
 
 public class AzureDiscoveryStrategyFactoryTest {
+    @Rule
+    public WireMockRule wireMockRule = new WireMockRule(wireMockConfig().dynamicPort());
 
     @Test
     public void validConfiguration() {
@@ -51,4 +68,46 @@ private static DiscoveryStrategy createStrategy(String xmlFileName) {
         Iterator<DiscoveryStrategy> strategies = service.getDiscoveryStrategies().iterator();
         return strategies.next();
     }
+
+    @Test
+    public void isEndpointAvailable() {
+        // given
+        String endpoint = "/some-endpoint";
+        String url = String.format("http://localhost:%d%s", wireMockRule.port(), endpoint);
+        stubFor(get(urlEqualTo(endpoint)).willReturn(aResponse().withStatus(200).withBody("some-body")));
+
+        // when
+        boolean isAvailable = AzureDiscoveryStrategyFactory.isEndpointAvailable(url);
+
+        // then
+        assertTrue(isAvailable);
+    }
+
+    @Test
+    public void readFileContents()
+            throws IOException {
+        // given
+        String expectedContents = "Hello, world!\nThis is a test with Unicode ✓.";
+        String testFile = createTestFile(expectedContents);
+
+        // when
+        String actualContents = AzureDiscoveryStrategyFactory.readFileContents(testFile);
+
+        // then
+        assertEquals(expectedContents, actualContents);
+    }
+
+    private static String createTestFile(String expectedContents)
+            throws IOException {
+        File temp = File.createTempFile("test", ".tmp");
+        temp.deleteOnExit();
+        BufferedWriter bufferedWriter = null;
+        try {
+            bufferedWriter = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(temp), StandardCharsets.UTF_8));
+            bufferedWriter.write(expectedContents);
+        } finally {
+            IOUtil.closeResource(bufferedWriter);
+        }
+        return temp.getAbsolutePath();
+    }
 }