Add healthcheck endpoints (#5543)

This PR adds readiness and liveness endpoints to probe Minio server
instance health. Endpoints can only be accessed without authentication
and the paths are /minio/health/live and /minio/health/ready for
liveness and readiness respectively.

The new healthcheck liveness endpoint is used for Docker healthcheck
now.

Fixes #5357
Fixes #5514

cmd/generic-handlers.go

@@ -193,6 +193,18 @@ func guessIsBrowserReq(req *http.Request) bool {
 	return strings.Contains(req.Header.Get("User-Agent"), "Mozilla")
 }
 
+// guessIsHealthCheckReq - returns true if incoming request looks
+// like healthcheck request
+func guessIsHealthCheckReq(req *http.Request) bool {
+	if req == nil {
+		return false
+	}
+	aType := getRequestAuthType(req)
+	return req.Method == http.MethodGet && aType == authTypeAnonymous &&
+		(req.URL.Path == healthCheckPathPrefix+healthCheckLivenessPath ||
+			req.URL.Path == healthCheckPathPrefix+healthCheckReadinessPath)
+}
+
 // guessIsRPCReq - returns true if the request is for an RPC endpoint.
 func guessIsRPCReq(req *http.Request) bool {
 	if req == nil {
@@ -263,7 +275,7 @@ func setReservedBucketHandler(h http.Handler) http.Handler {
 
 func (h minioReservedBucketHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	switch {
-	case guessIsRPCReq(r), guessIsBrowserReq(r), isAdminReq(r):
+	case guessIsRPCReq(r), guessIsBrowserReq(r), guessIsHealthCheckReq(r), isAdminReq(r):
 		// Allow access to reserved buckets
 	default:
 		// For all other requests reject access to reserved

cmd/healthcheck-handler.go

@@ -0,0 +1,69 @@
+/*
+ * Minio Cloud Storage, (C) 2018 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package cmd
+
+import (
+	"fmt"
+	"net/http"
+	"runtime"
+)
+
+const (
+	minioHealthGoroutineThreshold = 1000
+)
+
+// ReadinessCheckHandler -- checks if there are more than threshold number of goroutines running,
+// returns service unavailable.
+// Readiness probes are used to detect situations where application is under heavy load
+// and temporarily unable to serve. In a orchestrated setup like Kubernetes, containers reporting
+// that they are not ready do not receive traffic through Kubernetes Services.
+func ReadinessCheckHandler(w http.ResponseWriter, r *http.Request) {
+	if err := goroutineCountCheck(minioHealthGoroutineThreshold); err != nil {
+		writeResponse(w, http.StatusServiceUnavailable, nil, mimeNone)
+		return
+	}
+	writeResponse(w, http.StatusOK, nil, mimeNone)
+}
+
+// LivenessCheckHandler -- checks if server can ListBuckets internally. If not, server is
+// considered to have failed and needs to be restarted.
+// Liveness probes are used to detect situations where application (minio)
+// has gone into a state where it can not recover except by being restarted.
+func LivenessCheckHandler(w http.ResponseWriter, r *http.Request) {
+	objLayer := newObjectLayerFn()
+	// Service not initialized yet
+	if objLayer == nil {
+		writeResponse(w, http.StatusServiceUnavailable, nil, mimeNone)
+		return
+	}
+	// List buckets is unsuccessful, means server is having issues, send 503 service unavailable
+	if _, err := objLayer.ListBuckets(); err != nil {
+		writeResponse(w, http.StatusServiceUnavailable, nil, mimeNone)
+		return
+	}
+	writeResponse(w, http.StatusOK, nil, mimeNone)
+}
+
+// checks threshold against total number of go-routines in the system and throws error if
+// more than threshold go-routines are running.
+func goroutineCountCheck(threshold int) error {
+	count := runtime.NumGoroutine()
+	if count > threshold {
+		return fmt.Errorf("too many goroutines (%d > %d)", count, threshold)
+	}
+	return nil
+}

cmd/healthcheck-handler_test.go

@@ -0,0 +1,44 @@
+/*
+ * Minio Cloud Storage, (C) 2018 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package cmd
+
+import (
+	"testing"
+	"time"
+)
+
+func TestGoroutineCountCheck(t *testing.T) {
+	tests := []struct {
+		threshold int
+		wantErr   bool
+	}{
+		{5000, false},
+		{5, true},
+		{6, true},
+	}
+	for _, tt := range tests {
+		// Make goroutines -- to make sure number of go-routines is higher than threshold
+		if tt.threshold == 5 || tt.threshold == 6 {
+			for i := 0; i < 6; i++ {
+				go time.Sleep(5)
+			}
+		}
+		if err := goroutineCountCheck(tt.threshold); (err != nil) != tt.wantErr {
+			t.Errorf("goroutineCountCheck() error = %v, wantErr %v", err, tt.wantErr)
+		}
+	}
+}

cmd/healthcheck-router.go

@@ -0,0 +1,43 @@
+/*
+ * Minio Cloud Storage, (C) 2018 Minio, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package cmd
+
+import (
+	"net/http"
+
+	router "github.com/gorilla/mux"
+)
+
+const (
+	healthCheckPath          = "/health"
+	healthCheckLivenessPath  = "/live"
+	healthCheckReadinessPath = "/ready"
+	healthCheckPathPrefix    = minioReservedBucketPath + healthCheckPath
+)
+
+// registerHealthCheckRouter - add handler functions for liveness and readiness routes.
+func registerHealthCheckRouter(mux *router.Router) {
+
+	// Healthcheck router
+	healthRouter := mux.NewRoute().PathPrefix(healthCheckPathPrefix).Subrouter()
+
+	// Liveness handler
+	healthRouter.Methods(http.MethodGet).Path(healthCheckLivenessPath).HandlerFunc(LivenessCheckHandler)
+
+	// Readiness handler
+	healthRouter.Methods(http.MethodGet).Path(healthCheckReadinessPath).HandlerFunc(ReadinessCheckHandler)
+}

cmd/routers.go

@@ -73,6 +73,9 @@ func configureServerHandler(endpoints EndpointList) (http.Handler, error) {
 	// Add Admin router.
 	registerAdminRouter(mux)
 
+	// Add healthcheck router
+	registerHealthCheckRouter(mux)
+
 	// Register web router when its enabled.
 	if globalIsBrowserEnabled {
 		if err := registerWebRouter(mux); err != nil {

dockerscripts/healthcheck.sh

@@ -20,7 +20,7 @@ set -x
 _init () {
     scheme="http://"
     address="$(netstat -nplt 2>/dev/null | awk ' /(.*\/minio)/ { gsub(":::","127.0.0.1:",$4); print $4}')"
-    resource="/minio/index.html"
+    resource="/minio/health/live"
     start=$(stat -c "%Y" /proc/1)
 }
 
@@ -34,11 +34,10 @@ healthcheck_main () {
         exit 0
     else
         # Get the http response code
-        http_response=$(curl -H "User-Agent: Mozilla" -s -k -o /dev/null -I -w "%{http_code}" \
-            ${scheme}${address}${resource})
+        http_response=$(curl -s -k -o /dev/null -I -w "%{http_code}" ${scheme}${address}${resource})
 
         # Get the http response body
-        http_response_body=$(curl -H "User-Agent: Mozilla" -k -s ${scheme}${address}${resource})
+        http_response_body=$(curl -k -s ${scheme}${address}${resource})
 
         # server returns response 403 and body "SSL required" if non-TLS
         # connection is attempted on a TLS-configured server. Change
@@ -46,14 +45,11 @@ healthcheck_main () {
         if [ "$http_response" = "403" ] && \
         [ "$http_response_body" = "SSL required" ]; then
             scheme="https://"
-            http_response=$(curl -H "User-Agent: Mozilla" -s -k -o /dev/null -I -w "%{http_code}" \
-                ${scheme}${address}${resource})
+            http_response=$(curl -s -k -o /dev/null -I -w "%{http_code}" ${scheme}${address}${resource})
         fi
 
-        # If http_repsonse is 200 - server is up. When MINIO_BROWSER is
-        # set to off, curl responds with 404. We assume that the server
-        # is up
-        [ "$http_response" = "200" ] || [ "$http_response" = "404" ]
+        # If http_repsonse is 200 - server is up.
+        [ "$http_response" = "200" ]
     fi
 }
 

docs/healthcheck/README.md

@@ -0,0 +1,39 @@
+## Minio Healthcheck
+
+Minio server exposes two un-authenticated, healthcheck endpoints - liveness probe and readiness probe at `/minio/health/live` and `/minio/health/ready` respectively.
+
+### Liveness probe
+This probe is used to identify situations where the server is running but may not behave optimally, i.e. sluggish response or corrupt backend. Such problems can be *only* fixed by a restart.
+
+Internally, Minio liveness probe handler does a ListBuckets call. If successful, the server returns 200 OK, otherwise 503 Service Unavailable.
+
+When liveness probe fails, Kubernetes like platforms restart the container.
+
+Sample configuration in a Kubernetes `yaml` file.
+
+```yaml
+livenessProbe:
+  httpGet:
+    path: /minio/health/live
+    port: 9000
+  initialDelaySeconds: 10
+  periodSeconds: 20
+```
+
+### Readiness probe
+This probe is used to identify situations where the server is not ready to accept requests yet. In most cases, such conditions recover in some time.
+
+Internally, Minio readiness probe handler checks for total go-routines. If the number of go-routines is less than 1000 (threshold), the server returns 200 OK, otherwise 503 Service Unavailable.
+
+Platforms like Kubernetes *do not* forward traffic to a pod until its readiness probe is successful.
+
+Sample configuration in a Kubernetes `yaml` file.
+
+```yaml
+livenessProbe:
+  httpGet:
+    path: /minio/health/ready
+    port: 9000
+  initialDelaySeconds: 10
+  periodSeconds: 20
+```