support a flag configured to passthrough to env var

Author: djeebus

packages/api/internal/cfg/model.go

@@ -66,8 +66,6 @@ type Config struct {
 
 	DefaultKernelVersion string `env:"DEFAULT_KERNEL_VERSION"`
 
-	DefaultPersistentVolumeType string `env:"DEFAULT_PERSISTENT_VOLUME_TYPE"`
-
 	// SandboxStorageBackend selects the sandbox storage implementation.
 	// "redis" uses Redis directly; "populate_redis" uses in-memory with Redis shadow writes.
 	SandboxStorageBackend string `env:"SANDBOX_STORAGE_BACKEND" envDefault:"memory"`

packages/api/internal/handlers/volume_create.go

@@ -65,7 +65,7 @@ func (a *APIStore) PostVolumes(c *gin.Context) {
 
 	ctx = featureflags.AddToContext(ctx, featureflags.VolumeContext(body.Name))
 
-	volumeType := a.getVolumeType(ctx)
+	volumeType := a.featureFlags.StringFlag(ctx, featureflags.DefaultPersistentVolumeType)
 	if volumeType == "" {
 		a.sendAPIStoreError(c, http.StatusInternalServerError, "No persistent volume type is configured")
 		telemetry.ReportCriticalError(ctx, "default persistent volume type is not configured", nil)
@@ -165,15 +165,6 @@ func (a *APIStore) PostVolumes(c *gin.Context) {
 	c.JSON(http.StatusCreated, result)
 }
 
-func (a *APIStore) getVolumeType(ctx context.Context) string {
-	volumeType := a.featureFlags.StringFlag(ctx, featureflags.DefaultPersistentVolumeType)
-	if volumeType == "" {
-		volumeType = a.config.DefaultPersistentVolumeType
-	}
-
-	return volumeType
-}
-
 var validVolumeNameRegex = regexp.MustCompile(`^[a-zA-Z0-9_-]+$`)
 
 func isValidVolumeName(name string) bool {

packages/shared/pkg/featureflags/client.go

@@ -3,6 +3,7 @@ package featureflags
 import (
 	"context"
 	"os"
+	"reflect"
 	"time"
 
 	"github.com/launchdarkly/go-sdk-common/v3/ldcontext"
@@ -108,6 +109,7 @@ func (c *Client) StringFlag(ctx context.Context, flag StringFlag, contexts ...ld
 type typedFlag[T any] interface {
 	Key() string
 	Fallback() T
+	FallbackOnZero() bool
 }
 
 func getFlag[T any](
@@ -128,9 +130,18 @@ func getFlag[T any](
 		logger.L().Warn(ctx, "error evaluating flag", zap.Error(err), zap.String("flag", flag.Key()))
 	}
 
+	if flag.FallbackOnZero() && isZeroValue(value) {
+		return flag.Fallback()
+	}
+
 	return value
 }
 
+// isZeroValue returns true if the value is the zero value for its type.
+func isZeroValue[T any](v T) bool {
+	return reflect.ValueOf(&v).Elem().IsZero()
+}
+
 func (c *Client) Close(ctx context.Context) error {
 	if c.ld == nil {
 		return nil

packages/shared/pkg/featureflags/flags.go

@@ -3,6 +3,7 @@ package featureflags
 import (
 	"context"
 	"fmt"
+	"os"
 	"strings"
 
 	"github.com/launchdarkly/go-sdk-common/v3/ldcontext"
@@ -34,8 +35,9 @@ const (
 // All flags must be defined here: https://app.launchdarkly.com/projects/default/flags/
 
 type JSONFlag struct {
-	name     string
-	fallback ldvalue.Value
+	name           string
+	fallback       ldvalue.Value
+	fallbackOnZero bool
 }
 
 func (f JSONFlag) Key() string {
@@ -50,6 +52,10 @@ func (f JSONFlag) Fallback() ldvalue.Value {
 	return f.fallback
 }
 
+func (f JSONFlag) FallbackOnZero() bool {
+	return f.fallbackOnZero
+}
+
 func newJSONFlag(name string, fallback ldvalue.Value) JSONFlag {
 	flag := JSONFlag{name: name, fallback: fallback}
 	builder := launchDarklyOfflineStore.Flag(flag.name).ValueForAll(fallback)
@@ -88,6 +94,10 @@ func (f BoolFlag) Fallback() bool {
 	return f.fallback
 }
 
+func (f BoolFlag) FallbackOnZero() bool {
+	return false
+}
+
 func newBoolFlag(name string, fallback bool) BoolFlag {
 	flag := BoolFlag{name: name, fallback: fallback}
 	builder := launchDarklyOfflineStore.Flag(flag.name).VariationForAll(fallback)
@@ -122,8 +132,9 @@ var (
 )
 
 type IntFlag struct {
-	name     string
-	fallback int
+	name           string
+	fallback       int
+	fallbackOnZero bool
 }
 
 func (f IntFlag) Key() string {
@@ -138,6 +149,10 @@ func (f IntFlag) Fallback() int {
 	return f.fallback
 }
 
+func (f IntFlag) FallbackOnZero() bool {
+	return f.fallbackOnZero
+}
+
 func newIntFlag(name string, fallback int) IntFlag {
 	flag := IntFlag{name: name, fallback: fallback}
 	builder := launchDarklyOfflineStore.Flag(flag.name).ValueForAll(ldvalue.Int(fallback))
@@ -207,8 +222,9 @@ var (
 )
 
 type StringFlag struct {
-	name     string
-	fallback string
+	name                  string
+	fallback              string
+	fallbackOnEmptyString bool
 }
 
 func (f StringFlag) Key() string {
@@ -223,6 +239,10 @@ func (f StringFlag) Fallback() string {
 	return f.fallback
 }
 
+func (f StringFlag) FallbackOnZero() bool {
+	return f.fallbackOnEmptyString
+}
+
 func newStringFlag(name string, fallback string) StringFlag {
 	flag := StringFlag{name: name, fallback: fallback}
 	builder := launchDarklyOfflineStore.Flag(flag.name).ValueForAll(ldvalue.String(fallback))
@@ -231,6 +251,13 @@ func newStringFlag(name string, fallback string) StringFlag {
 	return flag
 }
 
+func newStringFlagFallbackOnEmptyString(name string, fallback string) StringFlag {
+	flag := newStringFlag(name, fallback)
+	flag.fallbackOnEmptyString = true
+
+	return flag
+}
+
 // This is currently not configurable via feature flags.
 const (
 	DefaultKernelVersion = "vmlinux-6.1.158"
@@ -251,9 +278,9 @@ var FirecrackerVersionMap = map[string]string{
 
 // BuildIoEngine Sync is used by default as there seems to be a bad interaction between Async and a lot of io operations.
 var (
-	BuildFirecrackerVersion     = newStringFlag("build-firecracker-version", env.GetEnv("DEFAULT_FIRECRACKER_VERSION", DefaultFirecrackerVersion))
+	BuildFirecrackerVersion     = newStringFlagFallbackOnEmptyString("build-firecracker-version", env.GetEnv("DEFAULT_FIRECRACKER_VERSION", DefaultFirecrackerVersion))
 	BuildIoEngine               = newStringFlag("build-io-engine", "Sync")
-	DefaultPersistentVolumeType = newStringFlag("default-persistent-volume-type", "")
+	DefaultPersistentVolumeType = newStringFlagFallbackOnEmptyString("default-persistent-volume-type", os.Getenv("DEFAULT_PERSISTENT_VOLUME_TYPE"))
 	BuildNodeInfo               = newJSONFlag("preferred-build-node", ldvalue.Null())
 	FirecrackerVersions         = newJSONFlag("firecracker-versions", ldvalue.FromJSONMarshal(FirecrackerVersionMap))
 )