Update healthcheck related examples and add head support (#5650)

- Add head method for healthcheck endpoint. Some platforms/users
may use the HTTP Head method to check for health status.

- Add liveness and readiness probe examples in Kubernetes yaml
example docs. Note that readiness probe not added to StatefulSet
example due to https://github.com/kubernetes/kubernetes/issues/27114

cmd/generic-handlers.go

@@ -200,7 +200,7 @@ func guessIsHealthCheckReq(req *http.Request) bool {
 		return false
 	}
 	aType := getRequestAuthType(req)
-	return req.Method == http.MethodGet && aType == authTypeAnonymous &&
+	return aType == authTypeAnonymous && (req.Method == http.MethodGet || req.Method == http.MethodHead) &&
 		(req.URL.Path == healthCheckPathPrefix+healthCheckLivenessPath ||
 			req.URL.Path == healthCheckPathPrefix+healthCheckReadinessPath)
 }

cmd/healthcheck-router.go

@@ -37,7 +37,9 @@ func registerHealthCheckRouter(mux *router.Router) {
 
 	// Liveness handler
 	healthRouter.Methods(http.MethodGet).Path(healthCheckLivenessPath).HandlerFunc(LivenessCheckHandler)
+	healthRouter.Methods(http.MethodHead).Path(healthCheckLivenessPath).HandlerFunc(LivenessCheckHandler)
 
 	// Readiness handler
 	healthRouter.Methods(http.MethodGet).Path(healthCheckReadinessPath).HandlerFunc(ReadinessCheckHandler)
+	healthRouter.Methods(http.MethodHead).Path(healthCheckReadinessPath).HandlerFunc(ReadinessCheckHandler)
 }

docs/healthcheck/README.md

@@ -3,37 +3,21 @@
 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.
+### Configuration example
 
-```yaml
-livenessProbe:
-  httpGet:
-    path: /minio/health/ready
-    port: 9000
-  initialDelaySeconds: 10
-  periodSeconds: 20
-```
+Sample `liveness` and `readiness` probe configuration in a Kubernetes `yaml` file can be found [here](https://github.com/minio/minio/blob/master/docs/orchestration/kubernetes-yaml/minio-standalone-deployment.yaml).

docs/orchestration/kubernetes-yaml/README.md

@@ -135,6 +135,24 @@ spec:
           value: "minio123"
         ports:
         - containerPort: 9000
+        # Readiness probe detects situations when Minio server instance
+        # is not ready to accept traffic. Kubernetes doesn't forward
+        # traffic to the pod till readiness checks fail.
+        readinessProbe:
+          httpGet:
+            path: /minio/health/ready
+            port: 9000
+          initialDelaySeconds: 120
+          periodSeconds: 20
+        # Liveness probe detects situations where Minio server instance
+        # is not working properly and needs restart. Kubernetes automatically
+        # restarts the pods if liveness checks fail.
+        livenessProbe:
+          httpGet:
+            path: /minio/health/live
+            port: 9000
+          initialDelaySeconds: 120
+          periodSeconds: 20
 ```
 
 Create the Deployment
@@ -298,6 +316,15 @@ spec:
         volumeMounts:
         - name: data
           mountPath: /data
+        # Liveness probe detects situations where Minio server instance
+        # is not working properly and needs restart. Kubernetes automatically
+        # restarts the pods if liveness checks fail.
+        livenessProbe:
+          httpGet:
+            path: /minio/health/live
+            port: 9000
+          initialDelaySeconds: 120
+          periodSeconds: 20
   # These are converted to volume claims by the controller
   # and mounted at the paths mentioned above.
   volumeClaimTemplates:

docs/orchestration/kubernetes-yaml/minio-distributed-statefulset.yaml

@@ -35,6 +35,15 @@ spec:
         volumeMounts:
         - name: data
           mountPath: /data
+        # Liveness probe detects situations where Minio server instance
+        # is not working properly and needs restart. Kubernetes automatically
+        # restarts the pods if liveness checks fail.
+        livenessProbe:
+          httpGet:
+            path: /minio/health/live
+            port: 9000
+          initialDelaySeconds: 120
+          periodSeconds: 20
   # These are converted to volume claims by the controller
   # and mounted at the paths mentioned above.
   volumeClaimTemplates:

docs/orchestration/kubernetes-yaml/minio-standalone-deployment.yaml

@@ -41,3 +41,21 @@ spec:
           value: "minio123"
         ports:
         - containerPort: 9000
+        # Readiness probe detects situations when Minio server instance
+        # is not ready to accept traffic. Kubernetes doesn't forward
+        # traffic to the pod while readiness checks fail.
+        readinessProbe:
+          httpGet:
+            path: /minio/health/ready
+            port: 9000
+          initialDelaySeconds: 120
+          periodSeconds: 20
+        # Liveness probe detects situations where Minio server instance
+        # is not working properly and needs restart. Kubernetes automatically
+        # restarts the pods if liveness checks fail.
+        livenessProbe:
+          httpGet:
+            path: /minio/health/live
+            port: 9000
+          initialDelaySeconds: 120
+          periodSeconds: 20