healthz check to avoid drain pod with last replicas

weed/server/volume_server.go

@@ -98,6 +98,7 @@ func NewVolumeServer(adminMux, publicMux *http.ServeMux, ip string,
 
 	handleStaticResources(adminMux)
 	adminMux.HandleFunc("/status", vs.statusHandler)
+	adminMux.HandleFunc("/healthz", vs.healthzHandler)
 	if signingKey == "" || enableUiAccess {
 		// only expose the volume server details for safe environments
 		adminMux.HandleFunc("/ui/index.html", vs.uiStatusHandler)

weed/server/volume_server_handlers_admin.go

@@ -1,6 +1,7 @@
 package weed_server
 
 import (
+	"github.com/chrislusf/seaweedfs/weed/topology"
 	"net/http"
 	"path/filepath"
 
@@ -9,6 +10,24 @@ import (
 	"github.com/chrislusf/seaweedfs/weed/util"
 )
 
+func (vs *VolumeServer) healthzHandler(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Server", "SeaweedFS Volume "+util.VERSION)
+	volumeInfos := vs.store.VolumeInfos()
+	for _, vinfo := range volumeInfos {
+		if len(vinfo.Collection) == 0 {
+			continue
+		}
+		if vinfo.ReplicaPlacement.GetCopyCount() > 1 {
+			_, err := topology.GetWritableRemoteReplications(vs.store, vs.grpcDialOption, vinfo.Id, vs.GetMaster)
+			if err != nil {
+				w.WriteHeader(http.StatusServiceUnavailable)
+				return
+			}
+		}
+	}
+	w.WriteHeader(http.StatusOK)
+}
+
 func (vs *VolumeServer) statusHandler(w http.ResponseWriter, r *http.Request) {
 	w.Header().Set("Server", "SeaweedFS Volume "+util.VERSION)
 	m := make(map[string]interface{})