adding sequential policy to forward plugin (#1704)

* adding sequential policy to forward plugin

* making sequential an alias to first in proxy plugin

man/coredns-forward.7

@@ -56,7 +56,7 @@ forward FROM TO\.\.\. {
     max_fails INTEGER
     tls CERT KEY CA
     tls_servername NAME
-    policy random|round_robin
+    policy random|round_robin|sequential
     health_check DURATION
 }
 .

plugin/forward/README.md

@@ -47,7 +47,7 @@ forward FROM TO... {
     max_fails INTEGER
     tls CERT KEY CA
     tls_servername NAME
-    policy random|round_robin
+    policy random|round_robin|sequential
     health_check DURATION
 }
 ~~~

plugin/forward/forward.go

@@ -193,6 +193,7 @@ type policy int
 const (
 	randomPolicy policy = iota
 	roundRobinPolicy
+	sequentialPolicy
 )
 
 const defaultTimeout = 5 * time.Second

plugin/forward/policy.go

@@ -53,3 +53,13 @@ func (r *roundRobin) List(p []*Proxy) []*Proxy {
 
 	return robin
 }
+
+// sequential is a policy that selects hosts based on sequential ordering.
+type sequential struct {}
+
+func (r *sequential) String() string { return "sequential" }
+
+func (r *sequential) List(p []*Proxy) []*Proxy {
+	return p
+}
+

plugin/forward/setup.go

@@ -225,6 +225,8 @@ func parseBlock(c *caddy.Controller, f *Forward) error {
 			f.p = &random{}
 		case "round_robin":
 			f.p = &roundRobin{}
+		case "sequential":
+			f.p = &sequential{}
 		default:
 			return c.Errf("unknown policy '%s'", x)
 		}

plugin/forward/setup_policy_test.go

@@ -17,6 +17,7 @@ func TestSetupPolicy(t *testing.T) {
 		// positive
 		{"forward . 127.0.0.1 {\npolicy random\n}\n", false, "random", ""},
 		{"forward . 127.0.0.1 {\npolicy round_robin\n}\n", false, "round_robin", ""},
+		{"forward . 127.0.0.1 {\npolicy sequential\n}\n", false, "sequential", ""},
 		// negative
 		{"forward . 127.0.0.1 {\npolicy random2\n}\n", true, "random", "unknown policy"},
 	}

plugin/pkg/healthcheck/policy.go

@@ -29,6 +29,9 @@ func init() {
 	RegisterPolicy("least_conn", func() Policy { return &LeastConn{} })
 	RegisterPolicy("round_robin", func() Policy { return &RoundRobin{} })
 	RegisterPolicy("first", func() Policy { return &First{} })
+        // 'sequential' is an alias to 'first' to maintain consistency with the forward plugin
+        // should probably remove 'first' in a future release
+	RegisterPolicy("sequential", func() Policy { return &First{} })
 }
 
 // Random is a policy that selects up hosts from a pool at random.

plugin/proxy/README.md

@@ -25,7 +25,7 @@ However, advanced features including load balancing can be utilized with an expa
 
 ~~~
 proxy FROM TO... {
-    policy random|least_conn|round_robin|first
+    policy random|least_conn|round_robin|sequential
     fail_timeout DURATION
     max_fails INTEGER
     health_check PATH:PORT [DURATION]
@@ -39,7 +39,7 @@ proxy FROM TO... {
 * **TO** is the destination endpoint to proxy to. At least one is required, but multiple may be
   specified. **TO** may be an IP:Port pair, or may reference a file in resolv.conf format
 * `policy` is the load balancing policy to use; applies only with multiple backends. May be one of
-  random, least_conn, round_robin or first. Default is random.
+  random, least_conn, round_robin or sequential. Default is random. 
 * `fail_timeout` specifies how long to consider a backend as down after it has failed. While it is
   down, requests will not be routed to that backend. A backend is "down" if CoreDNS fails to
   communicate with it. The default value is 2 seconds ("2s").
@@ -64,7 +64,8 @@ There are four load-balancing policies available:
 * `random` (default) - Randomly select a backend
 * `least_conn` - Select the backend with the fewest active connections
 * `round_robin` - Select the backend in round-robin fashion
-* `first` - Select the first available backend looking by order of declaration from left to right
+* `sequential` - Select the first available backend looking by order of declaration from left to right
+* `first` - Deprecated.  Use sequential instead
 
 
 All polices implement randomly spraying packets to backend hosts when *no healthy* hosts are