Fix issue where its possible for a component to receive a unit withou…

…t a config (#2138)

* Fix issue where checkinExpected channel might have out dated information.

* Run mage fmt.

* Add changelog entry.

* Increase rate lime for failure in test for slow CI runners.

* Cleanups from code review.

* Refactor the design of ensuring an initial expected comes from the observed message.

changelog/fragments/1674071325-Fix-issue-where-its-possible-for-a-component-to-receive-a-unit-without-a-config.yaml

@@ -0,0 +1,31 @@
+# Kind can be one of:
+# - breaking-change: a change to previously-documented behavior
+# - deprecation: functionality that is being removed in a later release
+# - bug-fix: fixes a problem in a previous version
+# - enhancement: extends functionality but does not break or fix existing behavior
+# - feature: new functionality
+# - known-issue: problems that we are aware of in a given version
+# - security: impacts on the security of a product or a user’s deployment.
+# - upgrade: important information for someone upgrading from a prior version
+# - other: does not fit into any of the other categories
+kind: feature
+
+# Change summary; a 80ish characters long description of the change.
+summary: Fix issue where its possible for a component to receive a unit without a config
+
+# Long description; in case the summary is not enough to describe the change
+# this field accommodate a description without length limits.
+#description:
+
+# Affected component; a word indicating the component this changeset affects.
+component:
+
+# PR number; optional; the PR number that added the changeset.
+# If not present is automatically filled by the tooling finding the PR where this changelog fragment has been added.
+# NOTE: the tooling supports backports, so it's able to fill the original PR number instead of the backport PR number.
+# Please provide it if you are adding a fragment for a different PR.
+pr: 2138
+
+# Issue number; optional; the GitHub issue related to this changeset (either closes or is part of).
+# If not present is automatically filled by the tooling with the issue linked to the PR number.
+issue: 2086

pkg/component/fake/component/main.go

@@ -12,6 +12,7 @@ import (
 	"io"
 	"os"
 	"os/signal"
+	"strconv"
 	"syscall"
 	"time"
 
@@ -46,7 +47,7 @@ func main() {
 }
 
 func run() error {
-	logger := zerolog.New(os.Stderr).With().Timestamp().Logger()
+	logger := zerolog.New(os.Stderr).Level(zerolog.TraceLevel).With().Timestamp().Logger()
 	ver := client.VersionInfo{
 		Name:    fake,
 		Version: "1.0",
@@ -347,7 +348,8 @@ type fakeInput struct {
 	state    client.UnitState
 	stateMsg string
 
-	canceller context.CancelFunc
+	canceller       context.CancelFunc
+	killerCanceller context.CancelFunc
 }
 
 func newFakeInput(logger zerolog.Logger, logLevel client.UnitLogLevel, manager *stateManager, unit *client.Unit, cfg *proto.UnitExpectedConfig) (*fakeInput, error) {
@@ -399,7 +401,7 @@ func newFakeInput(logger zerolog.Logger, logLevel client.UnitLogLevel, manager *
 		}
 	}()
 	i.canceller = cancel
-
+	i.parseConfig(cfg)
 	return i, nil
 }
 
@@ -429,6 +431,7 @@ func (f *fakeInput) Update(u *client.Unit) error {
 		return fmt.Errorf("unit type changed with the same unit ID: %s", config.Type)
 	}
 
+	f.parseConfig(config)
 	state, stateMsg, err := getStateFromConfig(config)
 	if err != nil {
 		return fmt.Errorf("unit config parsing error: %w", err)
@@ -440,6 +443,65 @@ func (f *fakeInput) Update(u *client.Unit) error {
 	return nil
 }
 
+func (f *fakeInput) parseConfig(config *proto.UnitExpectedConfig) {
+	// handle a case for killing the component when the pid of the component
+	// matches the current running PID
+	cfg := config.Source.AsMap()
+	killPIDRaw, kill := cfg["kill"]
+	if kill {
+		f.maybeKill(killPIDRaw)
+	}
+
+	// handle a case where random killing of the component is enabled
+	_, killOnInterval := cfg["kill_on_interval"]
+	f.logger.Trace().Bool("kill_on_interval", killOnInterval).Msg("kill_on_interval config set value")
+	if killOnInterval {
+		f.logger.Info().Msg("starting interval killer")
+		f.runKiller()
+	} else {
+		f.logger.Info().Msg("stopping interval killer")
+		f.stopKiller()
+	}
+}
+
+func (f *fakeInput) maybeKill(pidRaw interface{}) {
+	if killPID, ok := pidRaw.(string); ok {
+		if pid, err := strconv.Atoi(killPID); err == nil {
+			if pid == os.Getpid() {
+				f.logger.Warn().Msg("killing from config pid")
+				os.Exit(1)
+			}
+		}
+	}
+}
+
+func (f *fakeInput) runKiller() {
+	if f.killerCanceller != nil {
+		// already running
+		return
+	}
+	ctx, canceller := context.WithCancel(context.Background())
+	f.killerCanceller = canceller
+	go func() {
+		t := time.NewTimer(500 * time.Millisecond)
+		defer t.Stop()
+		select {
+		case <-ctx.Done():
+			return
+		case <-t.C:
+			f.logger.Warn().Msg("killer performing kill")
+			os.Exit(1)
+		}
+	}()
+}
+
+func (f *fakeInput) stopKiller() {
+	if f.killerCanceller != nil {
+		f.killerCanceller()
+		f.killerCanceller = nil
+	}
+}
+
 type stateSetterAction struct {
 	input *fakeInput
 }

pkg/component/fake/shipper/listener.go

@@ -10,6 +10,7 @@ import (
 	"fmt"
 	"net"
 	"os"
+	"path/filepath"
 	"strings"
 )
 
@@ -21,6 +22,13 @@ func createListener(path string) (net.Listener, error) {
 	if _, err := os.Stat(path); !os.IsNotExist(err) {
 		os.Remove(path)
 	}
+	dir := filepath.Dir(path)
+	if _, err := os.Stat(dir); os.IsNotExist(err) {
+		err := os.MkdirAll(dir, 0750)
+		if err != nil {
+			return nil, err
+		}
+	}
 	lis, err := net.Listen("unix", path)
 	if err != nil {
 		return nil, err

pkg/component/runtime/command.go

@@ -151,7 +151,7 @@ func (c *CommandRuntime) Run(ctx context.Context, comm Communicator) error {
 			sendExpected := c.state.syncExpected(&newComp)
 			changed := c.state.syncUnits(&newComp)
 			if sendExpected || c.state.unsettled() {
-				comm.CheckinExpected(c.state.toCheckinExpected())
+				comm.CheckinExpected(c.state.toCheckinExpected(), nil)
 			}
 			if changed {
 				c.sendObserved()
@@ -177,7 +177,7 @@ func (c *CommandRuntime) Run(ctx context.Context, comm Communicator) error {
 				sendExpected = true
 			}
 			if sendExpected {
-				comm.CheckinExpected(c.state.toCheckinExpected())
+				comm.CheckinExpected(c.state.toCheckinExpected(), checkin)
 			}
 			if changed {
 				c.sendObserved()
@@ -331,10 +331,6 @@ func (c *CommandRuntime) start(comm Communicator) error {
 	c.lastCheckin = time.Time{}
 	c.missedCheckins = 0
 
-	// Ensure there is no pending checkin expected message buffered to avoid sending the new process
-	// the expected state of the previous process: https://github.com/elastic/beats/issues/34137
-	comm.ClearPendingCheckinExpected()
-
 	proc, err := process.Start(path,
 		process.WithArgs(args),
 		process.WithEnv(env),

pkg/component/runtime/conn_info_server_test.go

@@ -57,7 +57,7 @@ func (c *mockCommunicator) WriteConnInfo(w io.Writer, services ...client.Service
 	return nil
 }
 
-func (c *mockCommunicator) CheckinExpected(expected *proto.CheckinExpected) {
+func (c *mockCommunicator) CheckinExpected(expected *proto.CheckinExpected, observed *proto.CheckinObserved) {
 }
 
 func (c *mockCommunicator) ClearPendingCheckinExpected() {