build distroless image (#16)

* use distroless/static base image

* implement stat for readinessProbe

build/Dockerfile

@@ -1,9 +1,12 @@
-FROM registry.access.redhat.com/ubi8/ubi-minimal:8.3
+FROM registry.access.redhat.com/ubi8/ubi-minimal:8.3 AS symlinker
 
-RUN mkdir -p /opt/jsonnet && chown nobody /opt/jsonnet
+ADD build/_output/bin/grafana-operator /usr/local/bin/grafana-operator
+RUN cd /usr/local/bin/ && ln -sf grafana-operator stat
+
+FROM gcr.io/distroless/static
 
 USER nobody
 
 ADD grafonnet-lib/grafonnet/ /opt/jsonnet/grafonnet
 
-ADD build/_output/bin/grafana-operator /usr/local/bin/grafana-operator
+COPY --from=symlinker /usr/local/bin/ /usr/local/bin/

cmd/manager/main.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"os"
+	"path"
 	"runtime"
 	"strings"
 
@@ -141,6 +142,16 @@ func getSanitizedNamespaceList() []string {
 	return selected
 }
 
+func handleReadinessProbe(path string) int {
+	if fileInfo, err := os.Stat(path); err != nil {
+		fmt.Println(err)
+		return 1
+	} else {
+		fmt.Println(fileInfo)
+		return 0
+	}
+}
+
 func main() {
 	// The logger instantiated here can be changed to any logger
 	// implementing the logr.Logger interface. This logger will
@@ -149,6 +160,11 @@ func main() {
 
 	logf.SetLogger(zap.Logger())
 
+	// handles calls to `stat ready-file` from readiness probe without external dependencies
+	if path.Base(os.Args[0]) == "stat" {
+		os.Exit(handleReadinessProbe(os.Args[1]))
+	}
+
 	printVersion()
 
 	namespace, err := k8sutil.GetWatchNamespace()