Improve Java logging (#8640)

java/runtime/src/main/resources/log4j.properties

@@ -1,17 +0,0 @@
-ray.logging.level=info
-
-ray.logging.stdout=org.apache.log4j.ConsoleAppender
-ray.logging.file=org.apache.log4j.varia.NullAppender
-
-log4j.rootLogger=${ray.logging.level}, stdout, file
-
-log4j.appender.stdout=${ray.logging.stdout}
-log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
-log4j.appender.stdout.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss,SSS} %p %c{1} [%t]: %m%n
-
-# Set the file appender to null by default. If `ray.redirect-output` config is set to true,
-# this appender will be set to a real file appender.
-log4j.appender.file=${ray.logging.file}
-log4j.appender.file.File=${ray.logging.file.path}
-log4j.appender.file.layout=org.apache.log4j.PatternLayout
-log4j.appender.file.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss,SSS} %p %c{1} [%t]: %m%n

java/runtime/src/main/resources/ray.default.conf

@@ -31,13 +31,20 @@ ray {
     resource-path: ""
   }
 
-  // Root dir of log files.
-  // If this is not set, the default log-dir will be `${temp-dir}/session_xxx/logs`.
-  log-dir: ""
-
-  // If true, output of worker processes will be redirected to log files.
-  // Otherwise, output will be printed to console.
-  redirect-output: true
+  // Configurations about logging.
+  logging {
+    // Level of logging for Java workers.
+    level: INFO
+    // Pattern of log messages.
+    pattern: "%d{yyyy-MM-dd HH:mm:ss,SSS} %p %c{1} [%t]: %m%n"
+    // Root directory of the log files.
+    // If this is not set, the default one will be `${temp-dir}/session_xxx/logs`.
+    dir: ""
+    // Maximum size that a log file is allowed to reach before being rolled over to backup files.
+    max-file-size: 500MB
+    // Maximum number of backup files to keep around.
+    max-backup-files: 10
+  }
 
   // Custom worker jvm parameters.
   worker.jvm-parameters: []