Merge pull request #1916 from weaveworks/issues/1734-fixed-ip

Support requesting a specific IP from the plugin

ipam/claim.go

@@ -75,6 +75,9 @@ func (c *claim) Try(alloc *Allocator) bool {
 	case "":
 		if err := alloc.space.Claim(c.addr); err == nil {
 			alloc.debugln("Claimed", c.addr, "for", c.ident)
+			if c.ident == "_" { // Special "I don't have a unique ID" identifier
+				c.ident = c.addr.String()
+			}
 			alloc.addOwned(c.ident, c.addr)
 			c.sendResult(nil)
 		} else {
@@ -84,6 +87,9 @@ func (c *claim) Try(alloc *Allocator) bool {
 		// same identifier is claiming same address; that's OK
 		alloc.debugln("Re-Claimed", c.addr, "for", c.ident)
 		c.sendResult(nil)
+	case c.addr.String():
+		// Address already allocated via "_" name
+		c.sendResult(fmt.Errorf("address %s already in use", c.addr))
 	default:
 		// Addr already owned by container on this machine
 		c.sendResult(fmt.Errorf("address %s is already owned by %s", c.addr.String(), existingIdent))