consul/connect: infer task name in service if possible

Before, the service definition for a Connect Native service would always
require setting the `service.task` parameter. Now, that parameter is
automatically inferred when there is only one task in the task group.

Fixes #8274

nomad/job_endpoint_hook_connect.go

@@ -6,6 +6,7 @@ import (
 
 	"github.com/hashicorp/nomad/helper/uuid"
 	"github.com/hashicorp/nomad/nomad/structs"
+	"github.com/pkg/errors"
 )
 
 var (
@@ -97,13 +98,23 @@ func isSidecarForService(t *structs.Task, svc string) bool {
 	return t.Kind == structs.TaskKind(fmt.Sprintf("%s:%s", structs.ConnectProxyPrefix, svc))
 }
 
-func getNamedTaskForNativeService(tg *structs.TaskGroup, taskName string) *structs.Task {
+// getNamedTaskForNativeService retrieves the Task with the name specified in the
+// group service definition. If the task name is empty and there is only one task
+// in the group, infer the name from the only option.
+func getNamedTaskForNativeService(tg *structs.TaskGroup, serviceName, taskName string) (*structs.Task, error) {
+	if taskName == "" {
+		if len(tg.Tasks) == 1 {
+			return tg.Tasks[0], nil
+		}
+		return nil, errors.Errorf("task for Consul Connect Native service %s->%s is ambiguous and must be set", tg.Name, serviceName)
+	}
+
 	for _, t := range tg.Tasks {
 		if t.Name == taskName {
-			return t
+			return t, nil
 		}
 	}
-	return nil
+	return nil, errors.Errorf("task %s named by Consul Connect Native service %s->%s does not exist", taskName, tg.Name, serviceName)
 }
 
 // probably need to hack this up to look for checks on the service, and if they
@@ -155,11 +166,13 @@ func groupConnectHook(job *structs.Job, g *structs.TaskGroup) error {
 			// create a port for the sidecar task's proxy port
 			makePort(fmt.Sprintf("%s-%s", structs.ConnectProxyPrefix, service.Name))
 		} else if service.Connect.IsNative() {
+			// find the task backing this connect native service and set the kind
 			nativeTaskName := service.TaskName
-			if t := getNamedTaskForNativeService(g, nativeTaskName); t != nil {
-				t.Kind = structs.NewTaskKind(structs.ConnectNativePrefix, service.Name)
+			if t, err := getNamedTaskForNativeService(g, service.Name, nativeTaskName); err != nil {
+				return err
 			} else {
-				return fmt.Errorf("native task %s named by %s->%s does not exist", nativeTaskName, g.Name, service.Name)
+				t.Kind = structs.NewTaskKind(structs.ConnectNativePrefix, service.Name)
+				service.TaskName = t.Name // in case the task was inferred
 			}
 		}
 	}
@@ -220,16 +233,8 @@ func groupConnectSidecarValidate(g *structs.TaskGroup) error {
 func groupConnectNativeValidate(g *structs.TaskGroup, s *structs.Service) error {
 	// note that network mode is not enforced for connect native services
 
-	// a native service must have the task identified in the service definition.
-	if len(s.TaskName) == 0 {
-		return fmt.Errorf("Consul Connect Native service %q requires task name", s.Name)
+	if _, err := getNamedTaskForNativeService(g, s.Name, s.TaskName); err != nil {
+		return err
 	}
-
-	// also make sure that task actually exists
-	for _, task := range g.Tasks {
-		if s.TaskName == task.Name {
-			return nil
-		}
-	}
-	return fmt.Errorf("Consul Connect Native service %q requires undefined task %q in group %q", s.Name, s.TaskName, g.Name)
+	return nil
 }

nomad/job_endpoint_hook_connect_test.go

@@ -157,32 +157,40 @@ func TestJobEndpointConnect_groupConnectSidecarValidate(t *testing.T) {
 	})
 }
 
-func TestJobEndpointConnect_groupConnectNativeValidate(t *testing.T) {
-	t.Run("no task in service", func(t *testing.T) {
-		require.EqualError(t, groupConnectNativeValidate(&structs.TaskGroup{
-			Name: "g1",
-		}, &structs.Service{
-			Name:     "s1",
-			TaskName: "",
-		}), `Consul Connect Native service "s1" requires task name`)
+func TestJobEndpointConnect_getNamedTaskForNativeService(t *testing.T) {
+	t.Run("named exists", func(t *testing.T) {
+		task, err := getNamedTaskForNativeService(&structs.TaskGroup{
+			Name:  "g1",
+			Tasks: []*structs.Task{{Name: "t1"}, {Name: "t2"}},
+		}, "s1", "t2")
+		require.NoError(t, err)
+		require.Equal(t, "t2", task.Name)
 	})
 
-	t.Run("no task for service", func(t *testing.T) {
-		require.EqualError(t, groupConnectNativeValidate(&structs.TaskGroup{
-			Name: "g2",
-		}, &structs.Service{
-			Name:     "s2",
-			TaskName: "t1",
-		}), `Consul Connect Native service "s2" requires undefined task "t1" in group "g2"`)
+	t.Run("infer exists", func(t *testing.T) {
+		task, err := getNamedTaskForNativeService(&structs.TaskGroup{
+			Name:  "g1",
+			Tasks: []*structs.Task{{Name: "t2"}},
+		}, "s1", "")
+		require.NoError(t, err)
+		require.Equal(t, "t2", task.Name)
 	})
 
-	t.Run("native okay", func(t *testing.T) {
-		require.NoError(t, groupConnectNativeValidate(&structs.TaskGroup{
-			Name:  "g2",
-			Tasks: []*structs.Task{{Name: "t0"}, {Name: "t1"}, {Name: "t3"}},
-		}, &structs.Service{
-			Name:     "s2",
-			TaskName: "t1",
-		}))
+	t.Run("infer ambiguous", func(t *testing.T) {
+		task, err := getNamedTaskForNativeService(&structs.TaskGroup{
+			Name:  "g1",
+			Tasks: []*structs.Task{{Name: "t1"}, {Name: "t2"}},
+		}, "s1", "")
+		require.EqualError(t, err, "task for Consul Connect Native service g1->s1 is ambiguous and must be set")
+		require.Nil(t, task)
+	})
+
+	t.Run("named absent", func(t *testing.T) {
+		task, err := getNamedTaskForNativeService(&structs.TaskGroup{
+			Name:  "g1",
+			Tasks: []*structs.Task{{Name: "t1"}, {Name: "t2"}},
+		}, "s1", "t3")
+		require.EqualError(t, err, "task t3 named by Consul Connect Native service g1->s1 does not exist")
+		require.Nil(t, task)
 	})
 }

nomad/structs/services.go

@@ -481,7 +481,8 @@ func (s *Service) Validate() error {
 			mErr.Errors = append(mErr.Errors, err)
 		}
 
-		// if service is connect native, service task must be set
+		// if service is connect native, service task must be set (which may
+		// happen implicitly in a job mutation if there is only one task)
 		if s.Connect.IsNative() && len(s.TaskName) == 0 {
 			mErr.Errors = append(mErr.Errors, fmt.Errorf("Service %s is Connect Native and requires setting the task", s.Name))
 		}

website/pages/docs/job-specification/service.mdx

@@ -149,8 +149,8 @@ Connect][connect] integration.
 
 - `task` `(string: "")` - Specifies the name of the Nomad Task associated with
   this service definition. Only available on group services. Must be set if this
-  service definition represents a Consul Connect Native service. The Nomad Task
-  must exist in the same Task Group.
+  service definition represents a Consul Connect Native service and there is more
+  than one task in the task group.
 
 - `meta` <code>([Meta][]: nil)</code> - Specifies a key-value map that annotates
   the Consul service with user-defined metadata.