Retry IP allocator claims

It may be that we cannot talk to a peer straight away, so allow claims
to be retried a few times before giving up.

ipam/claim.go

@@ -12,6 +12,7 @@ import (
 
 type claim struct {
 	resultChan       chan<- error
+	tryCount         int
 	ident            string       // a container ID, something like "weave:expose", or api.NoContainerID
 	cidr             address.CIDR // single address being claimed
 	isContainer      bool         // true if ident is a container ID
@@ -19,6 +20,8 @@ type claim struct {
 	hasBeenCancelled func() bool
 }
 
+const maxTryCount = 5
+
 // Send an error (or nil for success) back to caller listening on resultChan
 func (c *claim) sendResult(result error) {
 	// Make sure we only send a result once, since listener stops listening after that
@@ -40,6 +43,8 @@ func (c *claim) Try(alloc *Allocator) bool {
 		return true
 	}
 
+	c.tryCount++
+
 	addOwned := func() {
 		if c.ident == api.NoContainerID {
 			alloc.addOwned(c.cidr.Addr.String(), c.cidr, c.isContainer)
@@ -90,8 +95,10 @@ func (c *claim) Try(alloc *Allocator) bool {
 			if c.noErrorOnUnknown {
 				alloc.infof("Claim %s for %s: %s; will try later.", c.cidr, c.ident, err)
 				c.sendResult(nil)
-			} else { // just tell the user they can't do this.
-				c.deniedBy(alloc, owner)
+			} else if c.tryCount > maxTryCount {
+				// give up, tell the user they can't do this
+				c.deniedBy(alloc, owner, err)
+				return true
 			}
 		}
 		return false