From 4dd20447201bda5bde4a62800cb1ccfc89292c76 Mon Sep 17 00:00:00 2001
From: Thomas Hipp <thomas.hipp@pace.car>
Date: Wed, 8 Jan 2025 15:41:36 +0100
Subject: [PATCH] failover: Allow custom state setter

---
 maintenance/failover/failover.go     | 68 ++++++++++++++++++++++------
 maintenance/failover/state_setter.go | 53 ++++++++++++++++++++++
 2 files changed, 108 insertions(+), 13 deletions(-)
 create mode 100644 maintenance/failover/state_setter.go

diff --git a/maintenance/failover/failover.go b/maintenance/failover/failover.go
index 82df646c..d72f0872 100644
--- a/maintenance/failover/failover.go
+++ b/maintenance/failover/failover.go
@@ -11,7 +11,6 @@ import (
 	"time"
 
 	"github.com/bsm/redislock"
-	"github.com/pace/bricks/backend/k8sapi"
 	"github.com/pace/bricks/maintenance/errors"
 	"github.com/pace/bricks/maintenance/health"
 	"github.com/pace/bricks/maintenance/log"
@@ -26,8 +25,6 @@ const (
 	ACTIVE    status = 1
 )
 
-const Label = "github.com.pace.bricks.activepassive"
-
 // ActivePassive implements a failover mechanism that allows
 // to deploy a service multiple times but ony one will accept
 // traffic by using the label selector of kubernetes.
@@ -51,31 +48,76 @@ type ActivePassive struct {
 	timeToFailover time.Duration
 	locker         *redislock.Client
 
-	// access to the kubernetes api
-	k8sClient *k8sapi.Client
+	stateSetter StateSetter
 
 	// current status of the failover (to show it in the readiness status)
 	state   status
 	stateMu sync.RWMutex
 }
 
+type ActivePassiveOption func(*ActivePassive) error
+
+func WithCustomStateSetter(fn func(ctx context.Context, state string) error) ActivePassiveOption {
+	return func(ap *ActivePassive) error {
+		stateSetter, err := NewCustomStateSetter(fn)
+		if err != nil {
+			return fmt.Errorf("failed to create state setter: %w", err)
+		}
+
+		ap.stateSetter = stateSetter
+
+		return nil
+	}
+}
+
+func WithNoopStateSetter() ActivePassiveOption {
+	return func(ap *ActivePassive) error {
+		ap.stateSetter = &NoopStateSetter{}
+
+		return nil
+	}
+}
+
+func WithPodStateSetter() ActivePassiveOption {
+	return func(ap *ActivePassive) error {
+		stateSetter, err := NewPodStateSetter()
+		if err != nil {
+			return fmt.Errorf("failed to create pod state setter: %w", err)
+		}
+
+		ap.stateSetter = stateSetter
+
+		return nil
+	}
+}
+
 // NewActivePassive creates a new active passive cluster
 // identified by the name. The time to fail over determines
 // the frequency of checks performed against redis to
 // keep the active state.
 // NOTE: creating multiple ActivePassive in one process
 // is not working correctly as there is only one readiness probe.
-func NewActivePassive(clusterName string, timeToFailover time.Duration, client *redis.Client) (*ActivePassive, error) {
-	k8sClient, err := k8sapi.NewClient()
-	if err != nil {
-		return nil, err
-	}
-
+func NewActivePassive(clusterName string, timeToFailover time.Duration, client *redis.Client, opts ...ActivePassiveOption) (*ActivePassive, error) {
 	activePassive := &ActivePassive{
 		clusterName:    clusterName,
 		timeToFailover: timeToFailover,
 		locker:         redislock.New(client),
-		k8sClient:      k8sClient,
+	}
+
+	for _, opt := range opts {
+		if err := opt(activePassive); err != nil {
+			return nil, fmt.Errorf("failed to apply option: %w", err)
+		}
+	}
+
+	if activePassive.stateSetter == nil {
+		var err error
+
+		// Default state setter uses the k8s api to set the state.
+		activePassive.stateSetter, err = NewPodStateSetter()
+		if err != nil {
+			return nil, fmt.Errorf("failed to create default state setter: %w", err)
+		}
 	}
 
 	health.SetCustomReadinessCheck(activePassive.Handler)
@@ -198,7 +240,7 @@ func (a *ActivePassive) becomeUndefined(ctx context.Context) {
 
 // setState returns true if the state was set successfully
 func (a *ActivePassive) setState(ctx context.Context, state status) bool {
-	err := a.k8sClient.SetCurrentPodLabel(ctx, Label, a.label(state))
+	err := a.stateSetter.SetState(ctx, a.label(state))
 	if err != nil {
 		log.Ctx(ctx).Error().Err(err).Msg("failed to mark pod as undefined")
 		a.stateMu.Lock()
diff --git a/maintenance/failover/state_setter.go b/maintenance/failover/state_setter.go
new file mode 100644
index 00000000..d818ee4c
--- /dev/null
+++ b/maintenance/failover/state_setter.go
@@ -0,0 +1,53 @@
+package failover
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/pace/bricks/backend/k8sapi"
+)
+
+const Label = "github.com.pace.bricks.activepassive"
+
+type StateSetter interface {
+	SetState(ctx context.Context, state string) error
+}
+
+type podStateSetter struct {
+	k8sClient *k8sapi.Client
+}
+
+func NewPodStateSetter() (*podStateSetter, error) {
+	k8sClient, err := k8sapi.NewClient()
+	if err != nil {
+		return nil, fmt.Errorf("failed to create k8s client: %w", err)
+	}
+
+	return &podStateSetter{k8sClient: k8sClient}, nil
+}
+
+func (p *podStateSetter) SetState(ctx context.Context, state string) error {
+	return p.k8sClient.SetCurrentPodLabel(ctx, Label, state)
+}
+
+type CustomStateSetter struct {
+	fn func(ctx context.Context, state string) error
+}
+
+func NewCustomStateSetter(fn func(ctx context.Context, state string) error) (*CustomStateSetter, error) {
+	if fn == nil {
+		return nil, fmt.Errorf("fn must not be nil")
+	}
+
+	return &CustomStateSetter{fn: fn}, nil
+}
+
+func (c *CustomStateSetter) SetState(ctx context.Context, state string) error {
+	return c.fn(ctx, state)
+}
+
+type NoopStateSetter struct{}
+
+func (n *NoopStateSetter) SetState(ctx context.Context, state string) error {
+	return nil
+}