Merge pull request #2150 from weaveworks/issues/2139-zero-quorum

Don't try to form IPAM ring with a bogus quorum size

Fixes #2139.

ipam/allocator.go

@@ -86,7 +86,7 @@ func NewAllocator(config Config) *Allocator {
 	if config.IsObserver {
 		participant = paxos.NewObserver()
 	} else {
-		participant = paxos.NewNode(config.OurName, config.OurUID, 1)
+		participant = paxos.NewNode(config.OurName, config.OurUID, 0)
 	}
 	return &Allocator{
 		ourName:     config.OurName,

ipam/allocator_test.go

@@ -117,6 +117,7 @@ func TestBootstrap(t *testing.T) {
 
 	CheckAllExpectedMessagesSent(alloc1, alloc2)
 
+	// Check that tryPendingOps doesn't cause anything to happen here
 	alloc1.actionChan <- func() { alloc1.tryPendingOps() }
 	AssertNothingSent(t, done)
 
@@ -129,14 +130,24 @@ func TestBootstrap(t *testing.T) {
 	ExpectBroadcastMessage(alloc1, nil)
 	alloc1.OnGossipBroadcast(alloc2.ourName, alloc2.Encode())
 
-	// both nodes will get consensus now so initialize the ring
-	ExpectBroadcastMessage(alloc2, nil)
+	CheckAllExpectedMessagesSent(alloc1, alloc2)
+
+	// at this point, both nodes have seen each other, but don't have a valid proposal
+	// so there is another exchange of messages
 	ExpectBroadcastMessage(alloc2, nil)
 	alloc2.OnGossipBroadcast(alloc1.ourName, alloc1.Encode())
 
+	// we have consensus now so alloc1 will initialize the ring
+	ExpectBroadcastMessage(alloc1, nil)
+	alloc1.OnGossipBroadcast(alloc2.ourName, alloc2.Encode())
+
+	CheckAllExpectedMessagesSent(alloc1, alloc2)
+
+	// alloc2 receives the ring and does not reply
+	alloc2.OnGossipBroadcast(alloc1.ourName, alloc1.Encode())
+
 	CheckAllExpectedMessagesSent(alloc1, alloc2)
 
-	alloc1.OnGossipBroadcast(alloc2.ourName, alloc2.Encode())
 	// now alloc1 should have space
 
 	AssertSent(t, done)

ipam/paxos/paxos.go

@@ -241,6 +241,9 @@ func (node *Node) pickValue() Value {
 
 // Has a consensus been reached, based on the known claims of other nodes?
 func (node *Node) Consensus() (bool, AcceptedValue) {
+	if node.quorum == 0 {
+		return false, AcceptedValue{}
+	}
 	counts := map[ProposalID]uint{}
 
 	for _, claims := range node.knows {