✨ cache: add a synthetic delay to the cache server

Makefile

@@ -317,7 +317,7 @@ test-e2e-sharded: require-kind build-all build-kind-images
 	kind get kubeconfig > "$(WORK_DIR)/.kcp/kind.kubeconfig"
 	rm -f "$(WORK_DIR)/.kcp/ready-to-test"
 	UNSAFE_E2E_HACK_DISABLE_ETCD_FSYNC=true NO_GORUN=1 \
-		./bin/sharded-test-server --quiet --v=2 --log-dir-path="$(LOG_DIR)" --work-dir-path="$(WORK_DIR)" --shard-run-virtual-workspaces=false $(TEST_SERVER_ARGS) --number-of-shards=$(SHARDS) 2>&1 & PID=$$!; echo "PID $$PID" && \
+		./bin/sharded-test-server --quiet --v=2 --log-dir-path="$(LOG_DIR)" --work-dir-path="$(WORK_DIR)" --shard-run-virtual-workspaces=false $(TEST_SERVER_ARGS) --number-of-shards=$(SHARDS) --cache-synthetic-delay=500ms 2>&1 & PID=$$!; echo "PID $$PID" && \
 	trap 'kill -TERM $$PID' TERM INT EXIT && \
 	while [ ! -f "$(WORK_DIR)/.kcp/ready-to-test" ]; do sleep 1; done && \
 	NO_GORUN=1 GOOS=$(OS) GOARCH=$(ARCH) \

cmd/sharded-test-server/cache.go

@@ -39,7 +39,7 @@ import (
 	"github.com/kcp-dev/kcp/test/e2e/framework"
 )
 
-func startCacheServer(ctx context.Context, logDirPath, workingDir string) (<-chan error, string, error) {
+func startCacheServer(ctx context.Context, logDirPath, workingDir string, syntheticDelay time.Duration) (<-chan error, string, error) {
 	cyan := color.New(color.BgHiCyan, color.FgHiWhite).SprintFunc()
 	inverse := color.New(color.BgHiWhite, color.FgHiCyan).SprintFunc()
 	out := lineprefix.New(
@@ -59,6 +59,7 @@ func startCacheServer(ctx context.Context, logDirPath, workingDir string) (<-cha
 		"--embedded-etcd-client-port=8010",
 		"--embedded-etcd-peer-port=8011",
 		fmt.Sprintf("--secure-port=%d", cachePort),
+		fmt.Sprintf("--synthetic-delay=%s", syntheticDelay.String()),
 	)
 	fmt.Fprintf(out, "running: %v\n", strings.Join(commandLine, " "))
 	cmd := exec.CommandContext(ctx, commandLine[0], commandLine[1:]...) //nolint:gosec

cmd/sharded-test-server/main.go

@@ -24,6 +24,7 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"time"
 
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/types"
@@ -46,6 +47,7 @@ func main() {
 	logDirPath := flag.String("log-dir-path", "", "Path to the log files. If empty, log files are stored in the dot directories.")
 	workDirPath := flag.String("work-dir-path", "", "Path to the working directory where the .kcp* dot directories are created. If empty, the working directory is the current directory.")
 	numberOfShards := flag.Int("number-of-shards", 1, "The number of shards to create. The first created is assumed root.")
+	cacheSyntheticDelay := flag.Duration("cache-synthetic-delay", 0, "The duration of time the cache server will inject a delay for to all inbound requests.")
 	quiet := flag.Bool("quiet", false, "Suppress output of the subprocesses")
 
 	// split flags into --proxy-*, --shard-* and everything else (generic). The former are
@@ -62,13 +64,13 @@ func main() {
 	}
 	flag.CommandLine.Parse(genericFlags) //nolint:errcheck
 
-	if err := start(proxyFlags, shardFlags, *logDirPath, *workDirPath, *numberOfShards, *quiet); err != nil {
+	if err := start(proxyFlags, shardFlags, *logDirPath, *workDirPath, *numberOfShards, *quiet, *cacheSyntheticDelay); err != nil {
 		fmt.Println(err.Error())
 		os.Exit(1)
 	}
 }
 
-func start(proxyFlags, shardFlags []string, logDirPath, workDirPath string, numberOfShards int, quiet bool) error {
+func start(proxyFlags, shardFlags []string, logDirPath, workDirPath string, numberOfShards int, quiet bool, cacheSyntheticDelay time.Duration) error {
 	// We use a shutdown context to know that it's time to gather metrics, before stopping the shards, proxy, etc.
 	shutdownCtx, shutdownCancel := context.WithCancel(genericapiserver.SetupSignalContext())
 	defer shutdownCancel()
@@ -186,7 +188,7 @@ func start(proxyFlags, shardFlags []string, logDirPath, workDirPath string, numb
 
 	cacheServerErrCh := make(chan indexErrTuple)
 	cacheServerConfigPath := ""
-	cacheServerCh, configPath, err := startCacheServer(ctx, logDirPath, workDirPath)
+	cacheServerCh, configPath, err := startCacheServer(ctx, logDirPath, workDirPath, cacheSyntheticDelay)
 	if err != nil {
 		return fmt.Errorf("error starting the cache server: %w", err)
 	}

pkg/cache/server/config.go

@@ -141,6 +141,7 @@ func NewConfig(opts *cacheserveroptions.CompletedOptions, optionalLocalShardRest
 		apiHandler = filters.WithClusterScope(apiHandler)
 		apiHandler = WithShardScope(apiHandler)
 		apiHandler = WithServiceScope(apiHandler)
+		apiHandler = WithSyntheticDelay(apiHandler, opts.SyntheticDelay)
 		return apiHandler
 	}
 

pkg/cache/server/handler.go

@@ -22,6 +22,7 @@ import (
 	"net/url"
 	"regexp"
 	"strings"
+	"time"
 
 	apierrors "k8s.io/apimachinery/pkg/api/errors"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
@@ -141,3 +142,11 @@ func WithServiceScope(handler http.Handler) http.Handler {
 		handler.ServeHTTP(w, req)
 	})
 }
+
+// WithSyntheticDelay injects a synthetic delay to calls, to exacerbate timing issues and expose inconsistent client behavior.
+func WithSyntheticDelay(handler http.Handler, delay time.Duration) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		time.Sleep(delay)
+		handler.ServeHTTP(w, req)
+	})
+}

pkg/cache/server/options/options.go

@@ -17,6 +17,8 @@ limitations under the License.
 package options
 
 import (
+	"time"
+
 	"github.com/spf13/pflag"
 
 	genericoptions "k8s.io/apiserver/pkg/server/options"
@@ -34,6 +36,7 @@ type Options struct {
 	Authorization    *genericoptions.DelegatingAuthorizationOptions
 	APIEnablement    *genericoptions.APIEnablementOptions
 	EmbeddedEtcd     etcdoptions.Options
+	SyntheticDelay   time.Duration
 }
 
 type completedOptions struct {
@@ -44,6 +47,7 @@ type completedOptions struct {
 	Authorization    *genericoptions.DelegatingAuthorizationOptions
 	APIEnablement    *genericoptions.APIEnablementOptions
 	EmbeddedEtcd     etcdoptions.CompletedOptions
+	SyntheticDelay   time.Duration
 }
 
 type CompletedOptions struct {
@@ -113,4 +117,5 @@ func (o *Options) Complete() (*CompletedOptions, error) {
 func (o *Options) AddFlags(fs *pflag.FlagSet) {
 	o.EmbeddedEtcd.AddFlags(fs)
 	o.SecureServing.AddFlags(fs)
+	fs.DurationVar(&o.SyntheticDelay, "synthetic-delay", 0, "The duration of time the cache server will inject a delay for to all inbound requests. Useful for testing.")
 }