fix: don't log at error level in lease timeout

We don't want error alerts if a controller is just failing over, this PR adds some infrasturcture to allow for a lower level of error reporting when the errors all occur within the lease TTL.

fixes #2133

backend/controller/leader/leader.go

@@ -220,3 +220,71 @@ func (c *Coordinator[P]) retireFollower() {
 	f.cancelCtx()
 	c.follower = optional.None[*follower[P]]()
 }
+
+// ErrorFilter allows uses of leases to decide if an error might be due to the master falling over,
+// or is something else that will not resolve itself after the TTL
+type ErrorFilter struct {
+	leaseTTL time.Duration
+	// Error reporting utilities
+	// If a controller has failed over we don't want error logs while we are waiting for the lease to expire.
+	// This records error state and allows us to filter errors until we are past lease timeout
+	// and only reports the error if it persists
+	// firstErrorTime is the time of the first error, used to lower log levels if the errors all occur within a lease window
+	firstErrorTime      optional.Option[time.Time]
+	recordedSuccessTime optional.Option[time.Time]
+
+	// errorMutex protects firstErrorTime
+	errorMutex sync.Mutex
+}
+
+func NewErrorFilter(leaseTTL time.Duration) *ErrorFilter {
+	return &ErrorFilter{
+		errorMutex: sync.Mutex{},
+		leaseTTL:   leaseTTL,
+	}
+}
+
+// ReportLeaseError reports that an operation that relies on the leader being up has failed
+// If this is either the first report or the error is within the lease timeout duration from
+// the time of the first report it will return false, indicating that this may be a transient error
+// If it returns true then the error has persisted over the length of a lease, and is probably serious
+// this will also return true if some operations are succeeding and some are failing, indicating a non-lease
+// related transient error
+func (c *ErrorFilter) ReportLeaseError() bool {
+	c.errorMutex.Lock()
+	defer c.errorMutex.Unlock()
+	errorTime, ok := c.firstErrorTime.Get()
+	if !ok {
+		c.firstErrorTime = optional.Some(time.Now())
+		return false
+	}
+	// We have seen a success recorded, and a previous error
+	// within the lease timeout, this indicates transient errors are happening
+	if c.recordedSuccessTime.Ok() {
+		return true
+	}
+	if errorTime.Add(c.leaseTTL).After(time.Now()) {
+		// Within the lease window, it will probably be resolved when a new leader is elected
+		return false
+	}
+	return true
+}
+
+// ReportOperationSuccess reports that an operation that relies on the leader being up has succeeded
+// it is used to decide if an error is transient and will be fixed with a new leader, or if the error is persistent
+func (c *ErrorFilter) ReportOperationSuccess() {
+	c.errorMutex.Lock()
+	defer c.errorMutex.Unlock()
+	errorTime, ok := c.firstErrorTime.Get()
+	if !ok {
+		// Normal operation, no errors
+		return
+	}
+	if errorTime.Add(c.leaseTTL).After(time.Now()) {
+		c.recordedSuccessTime = optional.Some(time.Now())
+	} else {
+		// Outside the lease window, clear our state
+		c.recordedSuccessTime = optional.None[time.Time]()
+		c.firstErrorTime = optional.None[time.Time]()
+	}
+}

backend/controller/leader/leader_test.go

@@ -125,6 +125,33 @@ func TestSingleLeader(t *testing.T) {
 	ctxSlicesLock.Unlock()
 }
 
+func TestLeaseErrorFilteringPersistentError(t *testing.T) {
+	filter := NewErrorFilter(time.Millisecond * 200)
+	assert.False(t, filter.ReportLeaseError(), "first error should be filtered")
+	assert.False(t, filter.ReportLeaseError(), "second error should be filtered")
+	assert.False(t, filter.ReportLeaseError(), "third error should be filtered")
+	time.Sleep(time.Millisecond * 201)
+	assert.True(t, filter.ReportLeaseError(), "third error should be reported")
+}
+
+func TestLeaseErrorFilteringTransientError(t *testing.T) {
+	filter := NewErrorFilter(time.Millisecond * 200)
+	assert.False(t, filter.ReportLeaseError(), "first error should be filtered")
+	assert.False(t, filter.ReportLeaseError(), "second error should be filtered")
+	assert.False(t, filter.ReportLeaseError(), "third error should be filtered")
+	time.Sleep(time.Millisecond * 201)
+	filter.ReportOperationSuccess()
+	assert.False(t, filter.ReportLeaseError(), "first error again")
+}
+
+func TestLeaseErrorTransientErrors(t *testing.T) {
+	filter := NewErrorFilter(time.Millisecond * 200)
+	assert.False(t, filter.ReportLeaseError(), "first error should be filtered")
+	assert.False(t, filter.ReportLeaseError(), "second error should be filtered")
+	filter.ReportOperationSuccess()
+	assert.True(t, filter.ReportLeaseError(), "success and failure within the TTL should be reported")
+}
+
 func leaderFromCoordinators(t *testing.T, coordinators []*Coordinator[string]) (leaderIdx int, leaderStr string) {
 	t.Helper()
 

common/configuration/asm.go

@@ -53,18 +53,19 @@ func newASMForTesting(ctx context.Context, secretsClient *secretsmanager.Client,
 			return override, nil
 		}
 		rpcClient := rpc.Dial(ftlv1connect.NewAdminServiceClient, url.String(), log.Error)
-		return newASMFollower(rpcClient, url.String()), nil
+		return newASMFollower(rpcClient, url.String(), time.Second*10), nil
 	}
+	coordinator := leader.NewCoordinator[asmClient](
+		ctx,
+		advertise,
+		leases.SystemKey("asm"),
+		leaser,
+		time.Second*10,
+		leaderFactory,
+		followerFactory,
+	)
 	return &ASM{
-		coordinator: leader.NewCoordinator[asmClient](
-			ctx,
-			advertise,
-			leases.SystemKey("asm"),
-			leaser,
-			time.Second*10,
-			leaderFactory,
-			followerFactory,
-		),
+		coordinator: coordinator,
 	}
 }
 

common/configuration/asm_follower.go

@@ -3,6 +3,8 @@ package configuration
 import (
 	"context"
 	"fmt"
+	"github.com/TBD54566975/ftl/backend/controller/leader"
+	"github.com/TBD54566975/ftl/internal/log"
 	"net/url"
 	"time"
 
@@ -17,18 +19,17 @@ const asmFollowerSyncInterval = time.Second * 10
 
 // asmFollower uses AdminService to get/set secrets from the leader
 type asmFollower struct {
-	leaderName string
-
+	errorFilter *leader.ErrorFilter
+	leaderName  string
 	// client requests/responses use unobfuscated values
 	client ftlv1connect.AdminServiceClient
 }
 
-var _ asmClient = &asmFollower{}
-
-func newASMFollower(rpcClient ftlv1connect.AdminServiceClient, leaderName string) *asmFollower {
+func newASMFollower(rpcClient ftlv1connect.AdminServiceClient, leaderName string, leaseTTL time.Duration) *asmFollower {
 	f := &asmFollower{
-		leaderName: leaderName,
-		client:     rpcClient,
+		errorFilter: leader.NewErrorFilter(leaseTTL),
+		leaderName:  leaderName,
+		client:      rpcClient,
 	}
 	return f
 }
@@ -43,6 +44,7 @@ func (f *asmFollower) syncInterval() time.Duration {
 
 func (f *asmFollower) sync(ctx context.Context, values *xsync.MapOf[Ref, SyncedValue]) error {
 	// values must store obfuscated values, but f.client gives unobfuscated values
+	logger := log.FromContext(ctx)
 	obfuscator := Secrets{}.obfuscator()
 	module := ""
 	includeValues := true
@@ -51,7 +53,13 @@ func (f *asmFollower) sync(ctx context.Context, values *xsync.MapOf[Ref, SyncedV
 		IncludeValues: &includeValues,
 	}))
 	if err != nil {
-		return fmt.Errorf("error getting secrets list from leader: %w", err)
+		if f.errorFilter.ReportLeaseError() {
+			return fmt.Errorf("error getting secrets list from leader: %w", err)
+		}
+		logger.Warnf("error getting secrets list from leader, possible leader failover %s", err.Error())
+		return nil
+	} else {
+		f.errorFilter.ReportOperationSuccess()
 	}
 	visited := map[Ref]bool{}
 	for _, s := range resp.Msg.Secrets {

common/configuration/asm_test.go

@@ -11,6 +11,7 @@ import (
 	"path"
 	"sort"
 	"testing"
+	"time"
 
 	"connectrpc.com/connect"
 	"github.com/TBD54566975/ftl/backend/controller/leases"
@@ -181,7 +182,7 @@ func TestFollowerSync(t *testing.T) {
 
 	// fakeRPCClient connects the follower to the leader
 	fakeRPCClient := &fakeAdminClient{sm: leaderManager}
-	follower := newASMFollower(fakeRPCClient, "fake")
+	follower := newASMFollower(fakeRPCClient, "fake", time.Second)
 
 	followerASM := newASMForTesting(ctx, externalClient, URL("http://localhost:1235"), leaser, optional.Some[asmClient](follower))
 	asmClient, err := followerASM.coordinator.Get()