RATIS-1865. Add leader lease bound ratio configuration

ratis-common/src/main/java/org/apache/ratis/conf/ConfUtils.java

@@ -76,6 +76,15 @@ static BiConsumer<String, Integer> requireMax(int max) {
     };
   }
 
+  static BiConsumer<String, Double> requireMin(double min) {
+    return (key, value) -> {
+      if (value < min) {
+        throw new IllegalArgumentException(
+            key + " = " + value + " < min = " + min);
+      }
+    };
+  }
+
   static BiConsumer<String, Double> requireMax(double max) {
     return (key, value) -> {
       if (value > max) {

ratis-docs/src/site/markdown/configurations.md

@@ -185,6 +185,13 @@ treat the peer as caught-up. Increase this number when write throughput is high.
 
 --------------------------------------------------------------------------------
 
+| **Property**    | `raft.server.read.leader.lease.timeout.ratio` |
+|:----------------|:----------------------------------------------|
+| **Description** | maximum timeout ratio of leader lease         |
+| **Type**        | double, ranging from (0.0,1.0)                |
+| **Default**     | 0.9                                           |
+
+
 ### Write - Configurations related to write requests.
 
 * Limits on pending write requests

ratis-server-api/src/main/java/org/apache/ratis/server/RaftServerConfigKeys.java

@@ -191,6 +191,18 @@ static Option option(RaftProperties properties) {
     static void setOption(RaftProperties properties, Option option) {
       set(properties::setEnum, OPTION_KEY, option);
     }
+
+    String LEADER_LEASE_TIMEOUT_RATIO_KEY = PREFIX + ".leader.lease.timeout.ratio";
+    double LEADER_LEASE_TIMEOUT_RATIO_DEFAULT = 0.9;
+    static double leaderLeaseTimeoutRatio(RaftProperties properties) {
+      return getDouble(properties::getDouble, LEADER_LEASE_TIMEOUT_RATIO_KEY,
+          LEADER_LEASE_TIMEOUT_RATIO_DEFAULT, getDefaultLog(),
+          requireMin(0.0), requireMax(1.0));
+    }
+
+    static void setLeaderLeaseTimeoutRatio(RaftProperties properties, double ratio) {
+      setDouble(properties::setDouble, LEADER_LEASE_TIMEOUT_RATIO_KEY, ratio);
+    }
   }
 
   interface Write {

ratis-server/src/main/java/org/apache/ratis/server/impl/DivisionPropertiesImpl.java

@@ -28,13 +28,19 @@ class DivisionPropertiesImpl implements DivisionProperties {
   private final TimeDuration rpcTimeoutMax;
   private final TimeDuration rpcSleepTime;
   private final TimeDuration rpcSlownessTimeout;
+  private final TimeDuration leaderLeaseTimeout;
 
   DivisionPropertiesImpl(RaftProperties properties) {
     this.rpcTimeoutMin = RaftServerConfigKeys.Rpc.timeoutMin(properties);
     this.rpcTimeoutMax = RaftServerConfigKeys.Rpc.timeoutMax(properties);
     Preconditions.assertTrue(rpcTimeoutMax.compareTo(rpcTimeoutMin) >= 0,
         "rpcTimeoutMax = %s < rpcTimeoutMin = %s", rpcTimeoutMax, rpcTimeoutMin);
 
+    final double leaderLeaseTimeoutRatio = RaftServerConfigKeys.Read.leaderLeaseTimeoutRatio(properties);
+    this.leaderLeaseTimeout = this.rpcTimeoutMin.multiply(leaderLeaseTimeoutRatio);
+    Preconditions.assertTrue(rpcTimeoutMin.compareTo(leaderLeaseTimeout) >= 0,
+        "rpcTimeoutMin = %s < leaderLeaseTimeout = %s", rpcTimeoutMin, leaderLeaseTimeout);
+
     this.rpcSleepTime = RaftServerConfigKeys.Rpc.sleepTime(properties);
     this.rpcSlownessTimeout = RaftServerConfigKeys.Rpc.slownessTimeout(properties);
   }
@@ -49,6 +55,11 @@ public TimeDuration maxRpcTimeout() {
     return rpcTimeoutMax;
   }
 
+  /** @return the ratio of leader lease timeout */
+  public TimeDuration leaderLeaseTimeout() {
+    return leaderLeaseTimeout;
+  }
+
   @Override
   public TimeDuration rpcSleepTime() {
     return rpcSleepTime;