[8.10](backport #3383) Implement basic version negotiation with Fleet Server

.mockery.yaml

@@ -2,8 +2,4 @@ inpackage: False
 testonly: False
 with-expecter: True
 keeptree: True
-case: underscore
-note: |
-  Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
-  // or more contributor license agreements. Licensed under the Elastic License;
-  // you may not use this file except in compliance with the Elastic License.
+case: underscore

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

@@ -855,8 +855,12 @@ func (c *Coordinator) runLoopIteration(ctx context.Context) {
 
 	case configErr := <-c.managerChans.configManagerError:
 		if c.isManaged {
+			var wErr *WarningError
 			if configErr == nil {
 				c.setFleetState(agentclient.Healthy, "Connected")
+			} else if errors.As(configErr, &wErr) {
+				// we received a warning from Fleet, set state to degraded and the warning as state string
+				c.setFleetState(agentclient.Degraded, wErr.Error())
 			} else {
 				c.setFleetState(agentclient.Failed, configErr.Error())
 			}

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

@@ -222,6 +222,20 @@ func TestCoordinator_State_ConfigError_Managed(t *testing.T) {
 		return state.State == agentclient.Healthy && state.Message == "Running" && state.FleetState == agentclient.Healthy && state.FleetMessage == "Connected"
 	}, 3*time.Second, 10*time.Millisecond)
 
+	// report a warning
+	cfgMgr.ReportError(ctx, NewWarningError("some msg from Fleet"))
+	assert.Eventually(t, func() bool {
+		state := coord.State()
+		return state.State == agentclient.Healthy && state.Message == "Running" && state.FleetState == agentclient.Degraded && state.FleetMessage == "some msg from Fleet"
+	}, 3*time.Second, 10*time.Millisecond)
+
+	// recover from warning error
+	cfgMgr.ReportError(ctx, nil)
+	assert.Eventually(t, func() bool {
+		state := coord.State()
+		return state.State == agentclient.Healthy && state.Message == "Running" && state.FleetState == agentclient.Healthy && state.FleetMessage == "Connected"
+	}, 3*time.Second, 10*time.Millisecond)
+
 	cancel()
 	err = <-coordCh
 	require.NoError(t, err)

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

@@ -2,7 +2,7 @@
 // or more contributor license agreements. Licensed under the Elastic License;
 // you may not use this file except in compliance with the Elastic License.
 
-package gateway
+package coordinator
 
 import (
 	"context"
@@ -28,3 +28,16 @@ type FleetGateway interface {
 	// SetClient sets the client for the gateway.
 	SetClient(client.Sender)
 }
+
+// WarningError is emitted when we receive a warning in the Fleet response
+type WarningError struct {
+	msg string
+}
+
+func (w WarningError) Error() string {
+	return w.msg
+}
+
+func NewWarningError(warningMsg string) *WarningError {
+	return &WarningError{msg: warningMsg}
+}

internal/pkg/agent/application/gateway/fleet/fleet_gateway.go

@@ -12,7 +12,6 @@ import (
 
 	eaclient "github.com/elastic/elastic-agent-client/v7/pkg/client"
 	"github.com/elastic/elastic-agent/internal/pkg/agent/application/coordinator"
-	"github.com/elastic/elastic-agent/internal/pkg/agent/application/gateway"
 	"github.com/elastic/elastic-agent/internal/pkg/agent/application/info"
 	"github.com/elastic/elastic-agent/internal/pkg/agent/errors"
 	"github.com/elastic/elastic-agent/internal/pkg/core/backoff"
@@ -66,7 +65,7 @@ type stateStore interface {
 	Actions() []fleetapi.Action
 }
 
-type fleetGateway struct {
+type FleetGateway struct {
 	log                *logger.Logger
 	client             client.Sender
 	scheduler          scheduler.Scheduler
@@ -89,7 +88,7 @@ func New(
 	acker acker.Acker,
 	stateFetcher func() coordinator.State,
 	stateStore stateStore,
-) (gateway.FleetGateway, error) {
+) (*FleetGateway, error) {
 
 	scheduler := scheduler.NewPeriodicJitter(defaultGatewaySettings.Duration, defaultGatewaySettings.Jitter)
 	return newFleetGatewayWithScheduler(
@@ -113,8 +112,8 @@ func newFleetGatewayWithScheduler(
 	acker acker.Acker,
 	stateFetcher func() coordinator.State,
 	stateStore stateStore,
-) (gateway.FleetGateway, error) {
-	return &fleetGateway{
+) (*FleetGateway, error) {
+	return &FleetGateway{
 		log:          log,
 		client:       client,
 		settings:     settings,
@@ -128,11 +127,11 @@ func newFleetGatewayWithScheduler(
 	}, nil
 }
 
-func (f *fleetGateway) Actions() <-chan []fleetapi.Action {
+func (f *FleetGateway) Actions() <-chan []fleetapi.Action {
 	return f.actionCh
 }
 
-func (f *fleetGateway) Run(ctx context.Context) error {
+func (f *FleetGateway) Run(ctx context.Context) error {
 	// Backoff implementation doesn't support the use of a context [cancellation] as the shutdown mechanism.
 	// So we keep a done channel that will be closed when the current context is shutdown.
 	done := make(chan struct{})
@@ -174,11 +173,11 @@ func (f *fleetGateway) Run(ctx context.Context) error {
 }
 
 // Errors returns the channel to watch for reported errors.
-func (f *fleetGateway) Errors() <-chan error {
+func (f *FleetGateway) Errors() <-chan error {
 	return f.errCh
 }
 
-func (f *fleetGateway) doExecute(ctx context.Context, bo backoff.Backoff) (*fleetapi.CheckinResponse, error) {
+func (f *FleetGateway) doExecute(ctx context.Context, bo backoff.Backoff) (*fleetapi.CheckinResponse, error) {
 	bo.Reset()
 
 	// Guard if the context is stopped by a out of bound call,
@@ -222,7 +221,12 @@ func (f *fleetGateway) doExecute(ctx context.Context, bo backoff.Backoff) (*flee
 		}
 
 		f.checkinFailCounter = 0
-		f.errCh <- nil
+		if resp.FleetWarning != "" {
+			f.errCh <- coordinator.NewWarningError(resp.FleetWarning)
+		} else {
+			f.errCh <- nil
+		}
+
 		// Request was successful, return the collected actions.
 		return resp, nil
 	}
@@ -232,7 +236,7 @@ func (f *fleetGateway) doExecute(ctx context.Context, bo backoff.Backoff) (*flee
 	return nil, ctx.Err()
 }
 
-func (f *fleetGateway) convertToCheckinComponents(components []runtime.ComponentComponentState) []fleetapi.CheckinComponent {
+func (f *FleetGateway) convertToCheckinComponents(components []runtime.ComponentComponentState) []fleetapi.CheckinComponent {
 	if components == nil {
 		return nil
 	}
@@ -307,7 +311,7 @@ func (f *fleetGateway) convertToCheckinComponents(components []runtime.Component
 	return checkinComponents
 }
 
-func (f *fleetGateway) execute(ctx context.Context) (*fleetapi.CheckinResponse, time.Duration, error) {
+func (f *FleetGateway) execute(ctx context.Context) (*fleetapi.CheckinResponse, time.Duration, error) {
 	ecsMeta, err := info.Metadata(ctx, f.log)
 	if err != nil {
 		f.log.Error(errors.New("failed to load metadata", err))
@@ -367,15 +371,15 @@ func (f *fleetGateway) execute(ctx context.Context) (*fleetapi.CheckinResponse,
 }
 
 // shouldUnenroll checks if the max number of trying an invalid key is reached
-func (f *fleetGateway) shouldUnenroll() bool {
+func (f *FleetGateway) shouldUnenroll() bool {
 	return f.unauthCounter > maxUnauthCounter
 }
 
 func isUnauth(err error) bool {
 	return errors.Is(err, client.ErrInvalidAPIKey)
 }
 
-func (f *fleetGateway) SetClient(c client.Sender) {
+func (f *FleetGateway) SetClient(c client.Sender) {
 	f.client = c
 }
 

internal/pkg/agent/application/gateway/fleet/fleet_gateway_test.go

@@ -23,7 +23,6 @@ import (
 	"gotest.tools/assert"
 
 	"github.com/elastic/elastic-agent/internal/pkg/agent/application/coordinator"
-	"github.com/elastic/elastic-agent/internal/pkg/agent/application/gateway"
 	"github.com/elastic/elastic-agent/internal/pkg/agent/errors"
 	"github.com/elastic/elastic-agent/internal/pkg/agent/storage"
 	"github.com/elastic/elastic-agent/internal/pkg/agent/storage/store"
@@ -70,7 +69,7 @@ func newTestingClient() *testingClient {
 	return &testingClient{received: make(chan struct{}, 1)}
 }
 
-type withGatewayFunc func(*testing.T, gateway.FleetGateway, *testingClient, *scheduler.Stepper)
+type withGatewayFunc func(*testing.T, coordinator.FleetGateway, *testingClient, *scheduler.Stepper)
 
 func withGateway(agentInfo agentInfo, settings *fleetGatewaySettings, fn withGatewayFunc) func(t *testing.T) {
 	return func(t *testing.T) {
@@ -128,7 +127,7 @@ func TestFleetGateway(t *testing.T) {
 
 	t.Run("send no event and receive no action", withGateway(agentInfo, settings, func(
 		t *testing.T,
-		gateway gateway.FleetGateway,
+		gateway coordinator.FleetGateway,
 		client *testingClient,
 		scheduler *scheduler.Stepper,
 	) {
@@ -160,7 +159,7 @@ func TestFleetGateway(t *testing.T) {
 
 	t.Run("Successfully connects and receives a series of actions", withGateway(agentInfo, settings, func(
 		t *testing.T,
-		gateway gateway.FleetGateway,
+		gateway coordinator.FleetGateway,
 		client *testingClient,
 		scheduler *scheduler.Stepper,
 	) {
@@ -321,7 +320,7 @@ func TestRetriesOnFailures(t *testing.T) {
 	t.Run("When the gateway fails to communicate with the checkin API we will retry",
 		withGateway(agentInfo, settings, func(
 			t *testing.T,
-			gateway gateway.FleetGateway,
+			gateway coordinator.FleetGateway,
 			client *testingClient,
 			scheduler *scheduler.Stepper,
 		) {
@@ -369,7 +368,7 @@ func TestRetriesOnFailures(t *testing.T) {
 			Backoff:  backoffSettings{Init: 10 * time.Minute, Max: 20 * time.Minute},
 		}, func(
 			t *testing.T,
-			gateway gateway.FleetGateway,
+			gateway coordinator.FleetGateway,
 			client *testingClient,
 			scheduler *scheduler.Stepper,
 		) {
@@ -404,7 +403,7 @@ func emptyStateFetcher() coordinator.State {
 	return coordinator.State{}
 }
 
-func runFleetGateway(ctx context.Context, g gateway.FleetGateway) <-chan error {
+func runFleetGateway(ctx context.Context, g coordinator.FleetGateway) <-chan error {
 	done := make(chan bool)
 	errCh := make(chan error, 1)
 	go func() {

internal/pkg/agent/application/managed_mode.go

@@ -13,7 +13,6 @@ import (
 	"github.com/elastic/elastic-agent/internal/pkg/agent/application/actions/handlers"
 	"github.com/elastic/elastic-agent/internal/pkg/agent/application/coordinator"
 	"github.com/elastic/elastic-agent/internal/pkg/agent/application/dispatcher"
-	"github.com/elastic/elastic-agent/internal/pkg/agent/application/gateway"
 	fleetgateway "github.com/elastic/elastic-agent/internal/pkg/agent/application/gateway/fleet"
 	"github.com/elastic/elastic-agent/internal/pkg/agent/application/info"
 	"github.com/elastic/elastic-agent/internal/pkg/agent/application/paths"
@@ -223,7 +222,7 @@ func (m *managedConfigManager) Run(ctx context.Context) error {
 }
 
 // runDispatcher passes actions collected from gateway to dispatcher or calls Dispatch with no actions every flushInterval.
-func runDispatcher(ctx context.Context, actionDispatcher dispatcher.Dispatcher, fleetGateway gateway.FleetGateway, actionAcker acker.Acker, flushInterval time.Duration) {
+func runDispatcher(ctx context.Context, actionDispatcher dispatcher.Dispatcher, fleetGateway coordinator.FleetGateway, actionAcker acker.Acker, flushInterval time.Duration) {
 	t := time.NewTimer(flushInterval)
 	for {
 		select {

internal/pkg/fleetapi/checkin_cmd.go

@@ -77,8 +77,9 @@ func (e *CheckinRequest) Validate() error {
 // CheckinResponse is the response send back from the server which contains all the action that
 // need to be executed or proxy to running processes.
 type CheckinResponse struct {
-	AckToken string  `json:"ack_token"`
-	Actions  Actions `json:"actions"`
+	AckToken     string  `json:"ack_token"`
+	Actions      Actions `json:"actions"`
+	FleetWarning string  `json:"-"`
 }
 
 // Validate validates the response send from the server.
@@ -140,6 +141,7 @@ func (e *CheckinCmd) Execute(ctx context.Context, r *CheckinRequest) (*CheckinRe
 	}
 
 	checkinResponse := &CheckinResponse{}
+	checkinResponse.FleetWarning = resp.Header.Get("Warning")
 	decoder := json.NewDecoder(bytes.NewReader(rs))
 	if err := decoder.Decode(checkinResponse); err != nil {
 		return nil, sendDuration, errors.New(err,

internal/pkg/fleetapi/client/client.go

@@ -34,8 +34,14 @@ type Sender interface {
 	URI() string
 }
 
+// Default value for Elastic-Api-Version header when sending requests to Fleet (that's the only version we have at the time of writing)
+const defaultFleetApiVersion = "2023-06-01"
+
 var baseRoundTrippers = func(rt http.RoundTripper) (http.RoundTripper, error) {
 	rt = NewFleetUserAgentRoundTripper(rt, release.Version())
+
+	rt = NewElasticApiVersionRoundTripper(rt, defaultFleetApiVersion)
+
 	return rt, nil
 }