agent/local: support local alias checks

agent/local/state.go

@@ -170,8 +170,9 @@ type State struct {
 	// Services tracks the local services
 	services map[string]*ServiceState
 
-	// Checks tracks the local checks
+	// Checks tracks the local checks. checkAliases are aliased checks.
-	checks map[types.CheckID]*CheckState
+	checks       map[types.CheckID]*CheckState
+	checkAliases map[string]map[types.CheckID]chan<- struct{}
 
 	// metadata tracks the node metadata fields
 	metadata map[string]string
@@ -205,6 +206,7 @@ func NewState(c Config, lg *log.Logger, tokens *token.Store) *State {
 		logger:               lg,
 		services:             make(map[string]*ServiceState),
 		checks:               make(map[types.CheckID]*CheckState),
+		checkAliases:         make(map[string]map[types.CheckID]chan<- struct{}),
 		metadata:             make(map[string]string),
 		tokens:               tokens,
 		managedProxies:       make(map[string]*ManagedProxy),
@@ -406,6 +408,40 @@ func (l *State) AddCheck(check *structs.HealthCheck, token string) error {
 	return nil
 }
 
+// AddAliasCheck creates an alias check. When any check for the srcServiceID
+// is changed, checkID will reflect that using the same semantics as
+// checks.CheckAlias.
+//
+// This is a local optimization so that the Alias check doesn't need to
+// use blocking queries against the remote server for check updates for
+// local services.
+func (l *State) AddAliasCheck(checkID types.CheckID, srcServiceID string, notifyCh chan<- struct{}) error {
+	l.Lock()
+	defer l.Unlock()
+
+	m, ok := l.checkAliases[srcServiceID]
+	if !ok {
+		m = make(map[types.CheckID]chan<- struct{})
+		l.checkAliases[srcServiceID] = m
+	}
+	m[checkID] = notifyCh
+
+	return nil
+}
+
+// RemoveAliasCheck removes the mapping for the alias check.
+func (l *State) RemoveAliasCheck(checkID types.CheckID, srcServiceID string) {
+	l.Lock()
+	defer l.Unlock()
+
+	if m, ok := l.checkAliases[srcServiceID]; ok {
+		delete(m, checkID)
+		if len(m) == 0 {
+			delete(l.checkAliases, srcServiceID)
+		}
+	}
+}
+
 // RemoveCheck is used to remove a health check from the local state.
 // The agent will make a best effort to ensure it is deregistered
 // todo(fs): RemoveService returns an error for a non-existant service. RemoveCheck should as well.
@@ -486,6 +522,20 @@ func (l *State) UpdateCheck(id types.CheckID, status, output string) {
 		return
 	}
 
+	// If this is a check for an aliased service, then notify the waiters.
+	if aliases, ok := l.checkAliases[c.Check.ServiceID]; ok && len(aliases) > 0 {
+		for _, notifyCh := range aliases {
+			// Do not block. All notify channels should be buffered to at
+			// least 1 in which case not-blocking does not result in loss
+			// of data because a failed send means a notification is
+			// already queued.
+			select {
+			case notifyCh <- struct{}{}:
+			default:
+			}
+		}
+	}
+
 	// Update status and mark out of sync
 	c.Check.Status = status
 	c.Check.Output = output

agent/local/state_test.go

@@ -11,8 +11,6 @@ import (
 
 	"github.com/hashicorp/go-memdb"
 
-	"github.com/stretchr/testify/require"
-
 	"github.com/hashicorp/consul/agent"
 	"github.com/hashicorp/consul/agent/config"
 	"github.com/hashicorp/consul/agent/local"
@@ -23,6 +21,7 @@ import (
 	"github.com/hashicorp/consul/types"
 	"github.com/pascaldekloe/goe/verify"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestAgentAntiEntropy_Services(t *testing.T) {
@@ -1606,6 +1605,59 @@ func TestAgent_AddCheckFailure(t *testing.T) {
 	}
 }
 
+func TestAgent_AliasCheck(t *testing.T) {
+	t.Parallel()
+
+	require := require.New(t)
+	cfg := config.DefaultRuntimeConfig(`bind_addr = "127.0.0.1" data_dir = "dummy"`)
+	l := local.NewState(agent.LocalConfig(cfg), nil, new(token.Store))
+	l.TriggerSyncChanges = func() {}
+
+	// Add checks
+	require.NoError(l.AddService(&structs.NodeService{Service: "s1"}, ""))
+	require.NoError(l.AddService(&structs.NodeService{Service: "s2"}, ""))
+	require.NoError(l.AddCheck(&structs.HealthCheck{CheckID: types.CheckID("c1"), ServiceID: "s1"}, ""))
+	require.NoError(l.AddCheck(&structs.HealthCheck{CheckID: types.CheckID("c2"), ServiceID: "s2"}, ""))
+
+	// Add an alias
+	notifyCh := make(chan struct{}, 1)
+	require.NoError(l.AddAliasCheck(types.CheckID("a1"), "s1", notifyCh))
+
+	// Update and verify we get notified
+	l.UpdateCheck(types.CheckID("c1"), api.HealthCritical, "")
+	select {
+	case <-notifyCh:
+	case <-time.After(100 * time.Millisecond):
+		t.Fatal("notify not received")
+	}
+
+	// Update again and verify we do not get notified
+	l.UpdateCheck(types.CheckID("c1"), api.HealthCritical, "")
+	select {
+	case <-notifyCh:
+		t.Fatal("notify received")
+
+	case <-time.After(50 * time.Millisecond):
+	}
+
+	// Update other check and verify we do not get notified
+	l.UpdateCheck(types.CheckID("c2"), api.HealthCritical, "")
+	select {
+	case <-notifyCh:
+		t.Fatal("notify received")
+
+	case <-time.After(50 * time.Millisecond):
+	}
+
+	// Update change and verify we get notified
+	l.UpdateCheck(types.CheckID("c1"), api.HealthPassing, "")
+	select {
+	case <-notifyCh:
+	case <-time.After(100 * time.Millisecond):
+		t.Fatal("notify not received")
+	}
+}
+
 func TestAgent_sendCoordinate(t *testing.T) {
 	t.Parallel()
 	a := agent.NewTestAgent(t.Name(), `