RATIS-1446. Avoid leader election for invalid conf

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

@@ -43,15 +43,16 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Optional;
 import java.util.concurrent.Callable;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.ExecutorCompletionService;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.Future;
 import java.util.concurrent.atomic.AtomicInteger;
-import java.util.HashSet;
 import java.util.Set;
+import java.util.stream.Collectors;
 
 import static org.apache.ratis.util.LifeCycle.State.NEW;
 import static org.apache.ratis.util.LifeCycle.State.RUNNING;
@@ -104,7 +105,7 @@ enum Phase {
     ELECTION
   }
 
-  enum Result {PASSED, REJECTED, TIMEOUT, DISCOVERED_A_NEW_TERM, SHUTDOWN}
+  enum Result {PASSED, REJECTED, TIMEOUT, DISCOVERED_A_NEW_TERM, SHUTDOWN, NOT_IN_CONF}
 
   private static class ResultAndTerm {
     private final Result result;
@@ -271,6 +272,9 @@ private boolean shouldRun(long electionTerm) {
 
   private ResultAndTerm submitRequestAndWaitResult(Phase phase, RaftConfigurationImpl conf, long electionTerm)
       throws InterruptedException {
+    if (!conf.containsInConf(server.getId())) {
+      return new ResultAndTerm(Result.NOT_IN_CONF, electionTerm);
+    }
     final ResultAndTerm r;
     final Collection<RaftPeer> others = conf.getOtherPeers(server.getId());
     if (others.isEmpty()) {
@@ -315,6 +319,7 @@ private boolean askForVotes(Phase phase) throws InterruptedException, IOExceptio
         switch (r.getResult()) {
           case PASSED:
             return true;
+          case NOT_IN_CONF:
           case SHUTDOWN:
             server.getRaftServer().close();
             return false;
@@ -345,18 +350,12 @@ private int submitRequests(Phase phase, long electionTerm, TermIndex lastEntry,
   }
 
   private Set<RaftPeerId> getHigherPriorityPeers(RaftConfiguration conf) {
-    Set<RaftPeerId> higherPriorityPeers = new HashSet<>();
-
-    int currPriority = conf.getPeer(server.getId()).getPriority();
-    final Collection<RaftPeer> peers = conf.getAllPeers();
-
-    for (RaftPeer peer : peers) {
-      if (peer.getPriority() > currPriority) {
-        higherPriorityPeers.add(peer.getId());
-      }
-    }
-
-    return higherPriorityPeers;
+    final Optional<Integer> priority = Optional.ofNullable(conf.getPeer(server.getId()))
+        .map(RaftPeer::getPriority);
+    return conf.getAllPeers().stream()
+        .filter(peer -> priority.filter(p -> peer.getPriority() > p).isPresent())
+        .map(RaftPeer::getId)
+        .collect(Collectors.toSet());
   }
 
   private ResultAndTerm waitForResults(Phase phase, long electionTerm, int submitted,

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

@@ -912,17 +912,25 @@ private void yieldLeaderToHigherPriorityPeer() {
     }
 
     final RaftConfigurationImpl conf = server.getRaftConf();
-    int leaderPriority = conf.getPeer(server.getId()).getPriority();
+    final RaftPeer leader = conf.getPeer(server.getId());
+    if (leader == null) {
+      LOG.error("{} the leader {} is not in the conf {}", this, server.getId(), conf);
+      return;
+    }
+    int leaderPriority = leader.getPriority();
 
     for (LogAppender logAppender : senders.getSenders()) {
-      FollowerInfo followerInfo = logAppender.getFollower();
-      RaftPeerId followerID = followerInfo.getPeer().getId();
-      int followerPriority = conf.getPeer(followerID).getPriority();
-
+      final FollowerInfo followerInfo = logAppender.getFollower();
+      final RaftPeerId followerID = followerInfo.getPeer().getId();
+      final RaftPeer follower = conf.getPeer(followerID);
+      if (follower == null) {
+        LOG.error("{} the follower {} is not in the conf {}", this, server.getId(), conf);
+        continue;
+      }
+      final int followerPriority = follower.getPriority();
       if (followerPriority <= leaderPriority) {
         continue;
       }
-
       final TermIndex leaderLastEntry = server.getState().getLastEntry();
       if (leaderLastEntry == null) {
         LOG.info("{} send StartLeaderElectionRequest to follower:{} on term:{} because follower's priority:{} " +

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

@@ -144,7 +144,11 @@ boolean decideVote(RaftPeer candidate, TermIndex candidateLastEntry) {
     }
 
     // Check priority
-    final int priority = impl.getRaftConf().getPeer(impl.getId()).getPriority();
+    final RaftPeer peer = conf.getPeer(impl.getId());
+    if (peer == null) {
+      return reject("our server " + impl.getId() + " is not in the conf " + conf);
+    }
+    final int priority = peer.getPriority();
     if (priority <= candidate.getPriority()) {
       return log(true, "our priority " + priority + " <= candidate's priority " + candidate.getPriority());
     } else {