Allow starting without service endpoints

cmd/kube-httpcache/internal/flags.go

@@ -55,6 +55,8 @@ type KubeHTTPProxyFlags struct {
 		VCLTemplate          string
 		VCLTemplatePoll      bool
 		WorkingDir           string
+		FrontendInitTimeout  time.Duration
+		BackendInitTimeout   time.Duration
 	}
 	Readiness struct {
 		Enable  bool
@@ -107,6 +109,10 @@ func (f *KubeHTTPProxyFlags) Parse() error {
 	flag.StringVar(&f.Varnish.AdditionalParameters, "varnish-additional-parameters", "", "Additional Varnish start parameters (-p, seperated by comma), like 'ban_dups=on,cli_timeout=30'")
 	flag.BoolVar(&f.Varnish.VCLTemplatePoll, "varnish-vcl-template-poll", false, "poll for file changes instead of using inotify (useful on some network filesystems)")
 	flag.StringVar(&f.Varnish.WorkingDir, "varnish-working-dir", "", "varnish working directory (-n)")
+	flag.DurationVar(&f.Varnish.FrontendInitTimeout, "varnish-frontend-init-timeout", time.Duration(0),
+		"timeout for initial frontend configuration to be discovered. The default 0s means wait indefinitely. When timeout is reached, the controller will continue with an empty list of front-ends")
+	flag.DurationVar(&f.Varnish.BackendInitTimeout, "varnish-backend-init-timeout", time.Duration(0),
+		"timeout for initial backend configuration to be discovered. The default 0s means wait indefinitely. When timeout is reached, the controller will continue with an empty list of back-ends")
 
 	// present for BC only; no effect until #36 [1] has resolved
 	//   [1]: https://github.com/mittwald/kube-httpcache/issues/36

cmd/kube-httpcache/main.go

@@ -133,6 +133,8 @@ func main() {
 		templateUpdates,
 		varnishSignaller,
 		opts.Varnish.VCLTemplate,
+		opts.Varnish.FrontendInitTimeout,
+		opts.Varnish.BackendInitTimeout,
 	)
 	if err != nil {
 		panic(err)

pkg/controller/run.go

@@ -6,25 +6,53 @@ import (
 	"os"
 	"os/exec"
 	"strings"
+	"time"
 
 	"github.com/golang/glog"
 	"github.com/mittwald/kube-httpcache/pkg/watcher"
 )
 
+func (v *VarnishController) waitForUpdate(updatesChan chan *watcher.EndpointConfig, timeout time.Duration) (*watcher.EndpointConfig, error) {
+	var cancel context.CancelFunc
+	var ctx context.Context
+
+	ctx = context.Background()
+
+	if timeout > 0 {
+		ctx, cancel = context.WithTimeout(ctx, timeout)
+		defer cancel()
+	}
+
+	select {
+	case u := <-updatesChan:
+		return u, nil
+	case <-ctx.Done():
+		return nil, ctx.Err()
+	}
+}
+
 func (v *VarnishController) Run(ctx context.Context) error {
 	glog.Infof("waiting for initial configuration before starting Varnish")
 
 	v.frontend = watcher.NewEndpointConfig()
 	if v.frontendUpdates != nil {
-		v.frontend = <-v.frontendUpdates
+		if frontend, err := v.waitForUpdate(v.frontendUpdates, v.frontendInitTimeout); err == nil {
+			v.frontend = frontend
+		} else {
+			glog.Info("timeout while waiting for initial frontend configuration: %s", err.Error())
+		}
 		if v.varnishSignaller != nil {
 			v.varnishSignaller.SetEndpoints(v.frontend)
 		}
 	}
 
 	v.backend = watcher.NewEndpointConfig()
 	if v.backendUpdates != nil {
-		v.backend = <-v.backendUpdates
+		if backend, err := v.waitForUpdate(v.backendUpdates, v.backendInitTimeout); err == nil {
+			v.backend = backend
+		} else {
+			glog.Info("timeout while waiting for initial backend configuration: %s", err.Error())
+		}
 	}
 
 	target, err := os.Create(v.configFile)

pkg/controller/types.go

@@ -1,11 +1,13 @@
 package controller
 
 import (
-	"github.com/golang/glog"
 	"io"
 	"os"
 	"strings"
 	"text/template"
+	"time"
+
+	"github.com/golang/glog"
 
 	"github.com/mittwald/kube-httpcache/pkg/signaller"
 	"github.com/mittwald/kube-httpcache/pkg/watcher"
@@ -32,16 +34,17 @@ type VarnishController struct {
 
 	vclTemplate *template.Template
 	// md5 hash of unparsed template
-	vclTemplateHash    string
-	vclTemplateUpdates chan []byte
-	frontendUpdates    chan *watcher.EndpointConfig
-	frontend           *watcher.EndpointConfig
-	backendUpdates     chan *watcher.EndpointConfig
-	backend            *watcher.EndpointConfig
-	varnishSignaller   *signaller.Signaller
-	configFile         string
-	localAdminAddr     string
-	currentVCLName     string
+	vclTemplateHash     string
+	vclTemplateUpdates  chan []byte
+	frontendUpdates     chan *watcher.EndpointConfig
+	frontendInitTimeout time.Duration
+	backendInitTimeout  time.Duration
+	frontend            *watcher.EndpointConfig
+	backendUpdates      chan *watcher.EndpointConfig
+	backend             *watcher.EndpointConfig
+	varnishSignaller    *signaller.Signaller
+	configFile          string
+	currentVCLName      string
 }
 
 func NewVarnishController(
@@ -59,6 +62,8 @@ func NewVarnishController(
 	templateUpdates chan []byte,
 	varnishSignaller *signaller.Signaller,
 	vclTemplateFile string,
+	frontendInitTimeout time.Duration,
+	backendInitTimeout time.Duration,
 ) (*VarnishController, error) {
 	contents, err := os.ReadFile(vclTemplateFile)
 	if err != nil {
@@ -80,6 +85,8 @@ func NewVarnishController(
 		backendUpdates:       backendUpdates,
 		varnishSignaller:     varnishSignaller,
 		configFile:           "/tmp/vcl",
+		frontendInitTimeout:  frontendInitTimeout,
+		backendInitTimeout:   backendInitTimeout,
 	}
 	err = v.setTemplate(contents)
 	if err != nil {