Rework runtime manager updates to block the coordinator less

internal/pkg/agent/application/coordinator/coordinator.go

@@ -100,10 +100,7 @@ type RuntimeManager interface {
 	Runner
 
 	// Update updates the current components model.
-	Update(model component.Model) error
-
-	// State returns the current components model state.
-	State() []runtime.ComponentComponentState
+	Update(model component.Model)
 
 	// PerformAction executes an action on a unit.
 	PerformAction(ctx context.Context, comp component.Component, unit component.Unit, name string, params map[string]interface{}) (map[string]interface{}, error)
@@ -241,17 +238,19 @@ type Coordinator struct {
 	// into the reported state before broadcasting -- State() will report
 	// agentclient.Failed if one of these is set, even if the underlying
 	// coordinator state is agentclient.Healthy.
-	runtimeMgrErr error // Currently unused
-	configMgrErr  error
-	actionsErr    error
-	varsMgrErr    error
+	// Errors from the runtime manager report policy update failures and are
+	// stored in runtimeUpdateErr below.
+	configMgrErr error
+	actionsErr   error
+	varsMgrErr   error
 
 	// Errors resulting from different possible failure modes when setting a
 	// new policy. Right now there are three different stages where a policy
 	// update can fail:
 	// - in generateAST, converting the policy to an AST
 	// - in process, converting the AST and vars into a full component model
-	// - while sending the final component model to the runtime manager
+	// - while applying the final component model in the runtime manager
+	//   (reported asynchronously via the runtime manager error channel)
 	//
 	// The plan is to improve our preprocessing so we can always detect
 	// failures immediately https://github.com/elastic/elastic-agent/issues/2887.
@@ -920,7 +919,13 @@ func (c *Coordinator) runLoopIteration(ctx context.Context) {
 		return
 
 	case runtimeErr := <-c.managerChans.runtimeManagerError:
-		c.setRuntimeManagerError(runtimeErr)
+		// runtime manager errors report the result of a policy update.
+		// Coordinator transitions from starting to healthy when a policy update
+		// is successful.
+		c.setRuntimeUpdateError(runtimeErr)
+		if runtimeErr == nil {
+			c.setCoordinatorState(agentclient.Healthy, "Running")
+		}
 
 	case configErr := <-c.managerChans.configManagerError:
 		if c.isManaged {
@@ -1153,12 +1158,7 @@ func (c *Coordinator) refreshComponentModel(ctx context.Context) (err error) {
 
 	c.logger.Info("Updating running component model")
 	c.logger.With("components", model.Components).Debug("Updating running component model")
-	err = c.runtimeMgr.Update(model)
-	c.setRuntimeUpdateError(err)
-	if err != nil {
-		return fmt.Errorf("updating runtime: %w", err)
-	}
-	c.setCoordinatorState(agentclient.Healthy, "Running")
+	c.runtimeMgr.Update(model)
 	return nil
 }
 

internal/pkg/agent/application/coordinator/coordinator_state.go

@@ -63,10 +63,10 @@ func (c *Coordinator) SetUpgradeDetails(upgradeDetails *details.Details) {
 	c.upgradeDetailsChan <- upgradeDetails
 }
 
-// setRuntimeManagerError updates the error state for the runtime manager.
+// setRuntimeUpdateError reports a failed policy update in the runtime manager.
 // Called on the main Coordinator goroutine.
-func (c *Coordinator) setRuntimeManagerError(err error) {
-	c.runtimeMgrErr = err
+func (c *Coordinator) setRuntimeUpdateError(err error) {
+	c.runtimeUpdateErr = err
 	c.stateNeedsRefresh = true
 }
 
@@ -107,14 +107,6 @@ func (c *Coordinator) setComponentGenError(err error) {
 	c.stateNeedsRefresh = true
 }
 
-// setRuntimeUpdateError updates the error state for sending a component model
-// update to the runtime manager.
-// Called on the main Coordinator goroutine.
-func (c *Coordinator) setRuntimeUpdateError(err error) {
-	c.runtimeUpdateErr = err
-	c.stateNeedsRefresh = true
-}
-
 // setOverrideState is the internal helper to set the override state and
 // set stateNeedsRefresh.
 // Must be called on the main Coordinator goroutine.
@@ -201,9 +193,6 @@ func (c *Coordinator) generateReportableState() (s State) {
 	} else if c.runtimeUpdateErr != nil {
 		s.State = agentclient.Failed
 		s.Message = fmt.Sprintf("Runtime update failed: %s", c.runtimeUpdateErr.Error())
-	} else if c.runtimeMgrErr != nil {
-		s.State = agentclient.Failed
-		s.Message = fmt.Sprintf("Runtime manager: %s", c.runtimeMgrErr.Error())
 	} else if c.configMgrErr != nil {
 		s.State = agentclient.Failed
 		s.Message = fmt.Sprintf("Config manager: %s", c.configMgrErr.Error())

internal/pkg/agent/application/coordinator/coordinator_test.go

@@ -787,6 +787,8 @@ func (f *fakeVarsManager) Vars(ctx context.Context, vars []*transpiler.Vars) {
 type fakeRuntimeManager struct {
 	state          []runtime.ComponentComponentState
 	updateCallback func([]component.Component) error
+	result         error
+	errChan        chan error
 }
 
 func (r *fakeRuntimeManager) Run(ctx context.Context) error {
@@ -796,11 +798,15 @@ func (r *fakeRuntimeManager) Run(ctx context.Context) error {
 
 func (r *fakeRuntimeManager) Errors() <-chan error { return nil }
 
-func (r *fakeRuntimeManager) Update(model component.Model) error {
+func (r *fakeRuntimeManager) Update(model component.Model) {
+	r.result = nil
 	if r.updateCallback != nil {
-		return r.updateCallback(model.Components)
+		r.result = r.updateCallback(model.Components)
+	}
+	if r.errChan != nil {
+		// If a reporting channel is set, send the result to it
+		r.errChan <- r.result
 	}
-	return nil
 }
 
 // State returns the current components model state.

internal/pkg/agent/application/coordinator/coordinator_unit_test.go

@@ -754,13 +754,15 @@ func TestCoordinatorReportsRuntimeManagerUpdateFailure(t *testing.T) {
 	logger := logp.NewLogger("testing")
 
 	configChan := make(chan ConfigChange, 1)
+	updateErrChan := make(chan error, 1)
 
 	const errorStr = "update failed for testing reasons"
 	// Create a mocked runtime manager that always reports an error
 	runtimeManager := &fakeRuntimeManager{
 		updateCallback: func(comp []component.Component) error {
 			return fmt.Errorf(errorStr)
 		},
+		errChan: updateErrChan,
 	}
 
 	coord := &Coordinator{
@@ -769,6 +771,9 @@ func TestCoordinatorReportsRuntimeManagerUpdateFailure(t *testing.T) {
 		stateBroadcaster: broadcaster.New(State{}, 0, 0),
 		managerChans: managerChans{
 			configManagerUpdate: configChan,
+			// Give coordinator the same error channel we set on the runtime
+			// manager, so it receives the update result.
+			runtimeManagerError: updateErrChan,
 		},
 		runtimeMgr: runtimeManager,
 		vars:       emptyVars(t),
@@ -781,16 +786,19 @@ func TestCoordinatorReportsRuntimeManagerUpdateFailure(t *testing.T) {
 	configChan <- configChange
 	coord.runLoopIteration(ctx)
 
-	// Make sure the failure was reported to the config manager
-	assert.True(t, configChange.failed, "Config change should report failure if the runtime manager returns an error")
-	require.Error(t, configChange.err, "Config change should get an error if runtime manager update fails")
-	assert.Contains(t, configChange.err.Error(), errorStr)
+	// Make sure the config change was acknowledged to the config manager
+	// (the failure is not reported here since it happens asynchronously; it
+	// will appear in the coordinator state afterwards.)
+	assert.True(t, configChange.acked, "Config change should be acknowledged to the config manager")
+	assert.NoError(t, configChange.err, "Config change with async error should succeed")
 
-	// Make sure the error is saved in Coordinator.runtimeUpdateErr
+	// Now do another run loop iteration to let the update error propagate,
+	// and make sure it is reported correctly.
+	coord.runLoopIteration(ctx)
 	require.Error(t, coord.runtimeUpdateErr, "Runtime update failure should be saved in runtimeUpdateErr")
 	assert.Equal(t, errorStr, coord.runtimeUpdateErr.Error(), "runtimeUpdateErr should match the error reported by the runtime manager")
 
-	// Make sure the error is reported in Coordinator state.
+	// Make sure the error appears in the Coordinator state.
 	state := coord.State()
 	assert.Equal(t, agentclient.Failed, state.State, "Failed policy update should cause failed Coordinator")
 	assert.Contains(t, state.Message, errorStr, "Failed policy update should be reported in Coordinator state message")