Implement dynamic problemdaemon registration and initialization.

Added package problemdaemon. All future problem daemons should be
registered by calling problemdaemon.register().

CLI interfaces will be automatically generated for all registered
problem daemons in the form of "--config.DAEMON_NAME"

pkg/problemdaemon/problem_daemon.go

@@ -0,0 +1,73 @@
+/*
+Copyright 2019 The Kubernetes Authors All rights reserved.
+
+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 problemdaemon
+
+import (
+	"fmt"
+
+	"github.com/golang/glog"
+
+	"k8s.io/node-problem-detector/pkg/types"
+)
+
+var (
+	handlers = make(map[types.ProblemDaemonType]types.ProblemDaemonHandler)
+)
+
+// Register registers a problem daemon factory method, which will be used to create the problem daemon.
+func Register(problemDaemonType types.ProblemDaemonType, handler types.ProblemDaemonHandler) {
+	handlers[problemDaemonType] = handler
+}
+
+// GetProblemDaemonNames retrieves all available problem daemon types.
+func GetProblemDaemonNames() []types.ProblemDaemonType {
+	problemDaemonTypes := []types.ProblemDaemonType{}
+	for problemDaemonType := range handlers {
+		problemDaemonTypes = append(problemDaemonTypes, problemDaemonType)
+	}
+	return problemDaemonTypes
+}
+
+// GetProblemDaemonHandlerOrDie retrieves the ProblemDaemonHandler for a specific type of problem daemon, panic if error occurs..
+func GetProblemDaemonHandlerOrDie(problemDaemonType types.ProblemDaemonType) types.ProblemDaemonHandler {
+	handler, ok := handlers[problemDaemonType]
+	if !ok {
+		panic(fmt.Sprintf("Problem daemon handler for %v does not exist", problemDaemonType))
+	}
+	return handler
+}
+
+// NewProblemDaemons creates all problem daemons based on the configurations provided.
+func NewProblemDaemons(monitorConfigPaths types.ProblemDaemonConfigPathMap) []types.Monitor {
+	problemDaemonMap := make(map[string]types.Monitor)
+	for problemDaemonType, configs := range monitorConfigPaths {
+		for _, config := range *configs {
+			if _, ok := problemDaemonMap[config]; ok {
+				// Skip the config if it's duplicated.
+				glog.Warningf("Duplicated problem daemon configuration %q", config)
+				continue
+			}
+			problemDaemonMap[config] = handlers[problemDaemonType].CreateProblemDaemonOrDie(config)
+		}
+	}
+
+	problemDaemons := []types.Monitor{}
+	for _, problemDaemon := range problemDaemonMap {
+		problemDaemons = append(problemDaemons, problemDaemon)
+	}
+	return problemDaemons
+}

pkg/problemdaemon/problem_daemon_test.go

@@ -0,0 +1,72 @@
+/*
+Copyright 2019 The Kubernetes Authors All rights reserved.
+
+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 problemdaemon
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"k8s.io/node-problem-detector/pkg/types"
+)
+
+func TestRegistration(t *testing.T) {
+	fooMonitorFactory := func(configPath string) types.Monitor {
+		return nil
+	}
+	fooMonitorHandler := types.ProblemDaemonHandler{
+		CreateProblemDaemonOrDie: fooMonitorFactory,
+		CmdOptionDescription:     "foo option",
+	}
+
+	barMonitorFactory := func(configPath string) types.Monitor {
+		return nil
+	}
+	barMonitorHandler := types.ProblemDaemonHandler{
+		CreateProblemDaemonOrDie: barMonitorFactory,
+		CmdOptionDescription:     "bar option",
+	}
+
+	Register("foo", fooMonitorHandler)
+	Register("bar", barMonitorHandler)
+
+	expectedProblemDaemonNames := []types.ProblemDaemonType{"foo", "bar"}
+	problemDaemonNames := GetProblemDaemonNames()
+
+	assert.ElementsMatch(t, expectedProblemDaemonNames, problemDaemonNames)
+	assert.Equal(t, "foo option", GetProblemDaemonHandlerOrDie("foo").CmdOptionDescription)
+	assert.Equal(t, "bar option", GetProblemDaemonHandlerOrDie("bar").CmdOptionDescription)
+
+	handlers = make(map[types.ProblemDaemonType]types.ProblemDaemonHandler)
+}
+
+func TestGetProblemDaemonHandlerOrDie(t *testing.T) {
+	fooMonitorFactory := func(configPath string) types.Monitor {
+		return nil
+	}
+	fooMonitorHandler := types.ProblemDaemonHandler{
+		CreateProblemDaemonOrDie: fooMonitorFactory,
+		CmdOptionDescription:     "foo option",
+	}
+
+	Register("foo", fooMonitorHandler)
+
+	assert.NotPanics(t, func() { GetProblemDaemonHandlerOrDie("foo") })
+	assert.Panics(t, func() { GetProblemDaemonHandlerOrDie("bar") })
+
+	handlers = make(map[types.ProblemDaemonType]types.ProblemDaemonHandler)
+}