Retry all servers on RPC call failure

client/serverlist.go

@@ -0,0 +1,111 @@
+package client
+
+import (
+	"math/rand"
+	"net"
+	"sort"
+	"strings"
+	"sync"
+)
+
+// serverlist is a prioritized randomized list of nomad servers. Users should
+// call all() to retrieve the full list, followed by failed(e) on each endpoint
+// that's failed and good(e) when a valid endpoint is found.
+type serverlist struct {
+	e  endpoints
+	mu sync.RWMutex
+}
+
+func newServerList() *serverlist {
+	return &serverlist{}
+}
+
+// set the server list to a new list. The new list will be shuffled and sorted
+// by priority.
+func (s *serverlist) set(in endpoints) {
+	s.mu.Lock()
+	s.e = in
+	s.mu.Unlock()
+}
+
+// all returns a copy of the full server list, shuffled and then sorted by
+// priority
+func (s *serverlist) all() endpoints {
+	s.mu.RLock()
+	out := make(endpoints, len(s.e))
+	copy(out, s.e)
+	s.mu.RUnlock()
+
+	// Randomize the order
+	for i, j := range rand.Perm(len(out)) {
+		out[i], out[j] = out[j], out[i]
+	}
+
+	// Sort by priority
+	sort.Sort(out)
+	return out
+}
+
+// failed endpoint will be deprioritized if its still in the list.
+func (s *serverlist) failed(e *endpoint) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	for _, cur := range s.e {
+		if cur.equal(e) {
+			cur.priority++
+			return
+		}
+	}
+}
+
+// good endpoint will get promoted to the highest priority if it's still in the
+// list.
+func (s *serverlist) good(e *endpoint) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	for _, cur := range s.e {
+		if cur.equal(e) {
+			cur.priority = 0
+			return
+		}
+	}
+}
+
+func (e endpoints) Len() int {
+	return len(e)
+}
+
+func (e endpoints) Less(i int, j int) bool {
+	// Sort only by priority as endpoints should be shuffled and ordered
+	// only by priority
+	return e[i].priority < e[j].priority
+}
+
+func (e endpoints) Swap(i int, j int) {
+	e[i], e[j] = e[j], e[i]
+}
+
+type endpoints []*endpoint
+
+func (e endpoints) String() string {
+	names := make([]string, 0, len(e))
+	for _, endpoint := range e {
+		names = append(names, endpoint.name)
+	}
+	return strings.Join(names, ",")
+}
+
+type endpoint struct {
+	name string
+	addr net.Addr
+
+	// 0 being the highest priority
+	priority int
+}
+
+// equal returns true if the name and addr match between two endpoints.
+// Priority is ignored because the same endpoint may be added by discovery and
+// heartbeating with different priorities.
+func (e *endpoint) equal(o *endpoint) bool {
+	return e.name == o.name && e.addr == o.addr
+}

client/serverlist_test.go

@@ -0,0 +1,117 @@
+package client
+
+import (
+	"log"
+	"os"
+	"strings"
+	"testing"
+)
+
+func TestServerList(t *testing.T) {
+	s := newServerList()
+
+	// New lists should be empty
+	if e := s.all(); len(e) != 0 {
+		t.Fatalf("expected empty list to return an empty list, but received: %+q", e)
+	}
+
+	mklist := func() endpoints {
+		return endpoints{
+			&endpoint{"b", nil, 1},
+			&endpoint{"c", nil, 1},
+			&endpoint{"g", nil, 2},
+			&endpoint{"d", nil, 1},
+			&endpoint{"e", nil, 1},
+			&endpoint{"f", nil, 1},
+			&endpoint{"h", nil, 2},
+			&endpoint{"a", nil, 0},
+		}
+	}
+	s.set(mklist())
+
+	orig := mklist()
+	all := s.all()
+	if len(all) != len(orig) {
+		t.Fatalf("expected %d endpoints but only have %d", len(orig), len(all))
+	}
+
+	// Assert list is properly randomized+sorted
+	for i, pri := range []int{0, 1, 1, 1, 1, 1, 2, 2} {
+		if all[i].priority != pri {
+			t.Errorf("expected endpoint %d (%+q) to be priority %d", i, all[i], pri)
+		}
+	}
+
+	// Subsequent sets should reshuffle (try multiple times as they may
+	// shuffle in the same order)
+	tries := 0
+	max := 3
+	for ; tries < max; tries++ {
+		if s.all().String() == s.all().String() {
+			// eek, matched; try again in case we just got unlucky
+			continue
+		}
+		break
+	}
+	if tries == max {
+		t.Fatalf("after %d attempts servers were still not random reshuffled", tries)
+	}
+
+	// Mark an endpoint as failed enough that it should be at the end of the list
+	sa := &endpoint{"a", nil, 0}
+	s.failed(sa)
+	s.failed(sa)
+	s.failed(sa)
+	all2 := s.all()
+	if len(all2) != len(orig) {
+		t.Fatalf("marking should not have changed list length")
+	}
+	if all2[len(all)-1].name != sa.name {
+		t.Fatalf("failed endpoint should be at end of list: %+q", all2)
+	}
+
+	// But if the bad endpoint succeeds even once it should be bumped to the top group
+	s.good(sa)
+	found := false
+	for _, e := range s.all() {
+		if e.name == sa.name {
+			if e.priority != 0 {
+				t.Fatalf("server newly marked good should have highest priority")
+			}
+			found = true
+		}
+	}
+	if !found {
+		t.Fatalf("what happened to endpoint A?!")
+	}
+}
+
+// TestClient_ServerList tests client methods that interact with the internal
+// nomad server list.
+func TestClient_ServerList(t *testing.T) {
+	// manually create a mostly empty client to avoid spinning up a ton of
+	// goroutines that complicate testing
+	client := Client{servers: newServerList(), logger: log.New(os.Stderr, "", log.Ltime|log.Lshortfile)}
+
+	if s := client.GetServers(); len(s) != 0 {
+		t.Fatalf("expected server lit to be empty but found: %+q", s)
+	}
+	if err := client.SetServers(nil); err != noServersErr {
+		t.Fatalf("expected setting an empty list to return a 'no servers' error but received %v", err)
+	}
+	if err := client.SetServers([]string{"not-a-real-domain.fake"}); err == nil {
+		t.Fatalf("expected setting a bad server to return an error")
+	}
+	if err := client.SetServers([]string{"bad.fake", "127.0.0.1:1234", "127.0.0.1"}); err != nil {
+		t.Fatalf("expected setting at least one good server to succeed but received: %v", err)
+	}
+	s := client.GetServers()
+	if len(s) != 2 {
+		t.Fatalf("expected 2 servers but received: %+q", s)
+	}
+	for _, host := range s {
+		if !strings.HasPrefix(host, "127.0.0.1:") {
+			t.Errorf("expected both servers to be localhost and include port but found: %s", host)
+		}
+	}
+}