Parameterize host-ip to pass to tracker.py (#2831)

jvm-packages/xgboost4j/src/main/java/ml/dmlc/xgboost4j/java/RabitTracker.java

@@ -27,6 +27,7 @@ public class RabitTracker implements IRabitTracker {
   private static final Log logger = LogFactory.getLog(RabitTracker.class);
   // tracker python file.
   private static String tracker_py = null;
+  private static TrackerProperties trackerProperties = TrackerProperties.getInstance();
   // environment variable to be pased.
   private Map<String, String> envs = new HashMap<String, String>();
   // number of workers to be submitted.
@@ -129,8 +130,10 @@ public class RabitTracker implements IRabitTracker {
 
   private boolean startTrackerProcess() {
     try {
-      trackerProcess.set(Runtime.getRuntime().exec("python " + tracker_py +
+      String trackerExecString = this.addTrackerProperties("python " + tracker_py +
-              " --log-level=DEBUG --num-workers=" + String.valueOf(numWorkers)));
+          " --log-level=DEBUG --num-workers=" + String.valueOf(numWorkers));
+
+      trackerProcess.set(Runtime.getRuntime().exec(trackerExecString));
       loadEnvs(trackerProcess.get().getInputStream());
       return true;
     } catch (IOException ioe) {
@@ -139,6 +142,18 @@ public class RabitTracker implements IRabitTracker {
     }
   }
 
+  private String addTrackerProperties(String trackerExecString) {
+    StringBuilder sb = new StringBuilder(trackerExecString);
+    String hostIp = trackerProperties.getHostIp();
+
+    if(hostIp != null && !hostIp.isEmpty()){
+      logger.debug("Using provided host-ip: " + hostIp);
+      sb.append(" --host-ip=").append(hostIp);
+    }
+
+    return sb.toString();
+  }
+
   public void stop() {
     if (trackerProcess.get() != null) {
       trackerProcess.get().destroy();

jvm-packages/xgboost4j/src/main/java/ml/dmlc/xgboost4j/java/TrackerProperties.java

@@ -0,0 +1,56 @@
+package ml.dmlc.xgboost4j.java;
+
+import java.io.*;
+import java.net.URL;
+import java.util.Properties;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+
+public class TrackerProperties {
+  private static String PROPERTIES_FILENAME = "xgboost-tracker.properties";
+  private static String HOST_IP = "host-ip";
+
+  private static final Log logger = LogFactory.getLog(TrackerProperties.class);
+  private static TrackerProperties instance = new TrackerProperties();
+
+  private Properties properties;
+
+  private TrackerProperties() {
+    this.properties = new Properties();
+
+    InputStream inputStream = null;
+
+    try {
+      URL propertiesFileURL =
+          Thread.currentThread().getContextClassLoader().getResource(PROPERTIES_FILENAME);
+      if (propertiesFileURL != null){
+        inputStream = propertiesFileURL.openStream();
+      }
+    } catch (IOException e) {
+      logger.warn("Could not load " + PROPERTIES_FILENAME + " file. ", e);
+    }
+
+    if(inputStream != null){
+      try {
+        properties.load(inputStream);
+        logger.debug("Loaded properties from external source");
+      } catch (IOException e) {
+        logger.error("Error loading tracker properties file. Skipping and using defaults. ", e);
+      }
+      try {
+        inputStream.close();
+      } catch (IOException e) {
+        // ignore exception
+      }
+    }
+  }
+
+  public static TrackerProperties getInstance() {
+    return instance;
+  }
+
+  public String getHostIp(){
+    return this.properties.getProperty(HOST_IP);
+  }
+}