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"

cmd/options/options.go

@@ -24,18 +24,15 @@ import (
 	"net/url"
 
 	"github.com/spf13/pflag"
+
+	"k8s.io/node-problem-detector/pkg/problemdaemon"
+	"k8s.io/node-problem-detector/pkg/types"
 )
 
 // NodeProblemDetectorOptions contains node problem detector command line and application options.
 type NodeProblemDetectorOptions struct {
 	// command line options
 
-	// SystemLogMonitorConfigPaths specifies the list of paths to system log monitor configuration
-	// files.
-	SystemLogMonitorConfigPaths []string
-	// CustomPluginMonitorConfigPaths specifies the list of paths to custom plugin monitor configuration
-	// files.
-	CustomPluginMonitorConfigPaths []string
 	// PrintVersion is the flag determining whether version information is printed.
 	PrintVersion bool
 	// HostnameOverride specifies custom node name used to override hostname.
@@ -53,6 +50,17 @@ type NodeProblemDetectorOptions struct {
 	// ApiServerOverride is the custom URI used to connect to Kubernetes ApiServer.
 	ApiServerOverride string
 
+	// problem daemon options
+
+	// SystemLogMonitorConfigPaths specifies the list of paths to system log monitor configuration
+	// files.
+	SystemLogMonitorConfigPaths []string
+	// CustomPluginMonitorConfigPaths specifies the list of paths to custom plugin monitor configuration
+	// files.
+	CustomPluginMonitorConfigPaths []string
+	// MonitorConfigPaths specifies the list of paths to configuration files for each monitor.
+	MonitorConfigPaths types.ProblemDaemonConfigPathMap
+
 	// application options
 
 	// NodeName is the node name used to communicate with Kubernetes ApiServer.
@@ -60,7 +68,7 @@ type NodeProblemDetectorOptions struct {
 }
 
 func NewNodeProblemDetectorOptions() *NodeProblemDetectorOptions {
-	return &NodeProblemDetectorOptions{}
+	return &NodeProblemDetectorOptions{MonitorConfigPaths: types.ProblemDaemonConfigPathMap{}}
 }
 
 // AddFlags adds node problem detector command line options to pflag.
@@ -79,6 +87,17 @@ func (npdo *NodeProblemDetectorOptions) AddFlags(fs *pflag.FlagSet) {
 		20256, "The port to bind the node problem detector server. Use 0 to disable.")
 	fs.StringVar(&npdo.ServerAddress, "address",
 		"127.0.0.1", "The address to bind the node problem detector server.")
+
+	for _, problemDaemonName := range problemdaemon.GetProblemDaemonNames() {
+		npdo.MonitorConfigPaths[problemDaemonName] = &[]string{}
+		fs.StringSliceVar(
+			npdo.MonitorConfigPaths[problemDaemonName],
+			"config."+string(problemDaemonName),
+			[]string{},
+			fmt.Sprintf("Comma separated configurations for %v monitor. %v",
+				problemDaemonName,
+				problemdaemon.GetProblemDaemonHandlerOrDie(problemDaemonName).CmdOptionDescription))
+	}
 }
 
 // ValidOrDie validates node problem detector command line options.
@@ -90,6 +109,12 @@ func (npdo *NodeProblemDetectorOptions) ValidOrDie() {
 	if len(npdo.SystemLogMonitorConfigPaths) == 0 && len(npdo.CustomPluginMonitorConfigPaths) == 0 {
 		panic(fmt.Sprintf("Either --system-log-monitors or --custom-plugin-monitors is required"))
 	}
+
+	for problemDaemonName, configs := range npdo.MonitorConfigPaths {
+		if configs == nil {
+			panic(fmt.Sprintf("nil config for problem daemon %q. This should never happen, might indicates bug in pflag.", problemDaemonName))
+		}
+	}
 }
 
 // SetNodeNameOrDie sets `NodeName` field with valid value.

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)
+}

pkg/types/types.go

@@ -113,3 +113,20 @@ type Exporter interface {
 	// Export problems to the control plane.
 	ExportProblems(*Status)
 }
+
+// ProblemDaemonType is the type of the problem daemon.
+// One type of problem daemon may be used to initialize multiple problem daemon instances.
+type ProblemDaemonType string
+
+// ProblemDaemonConfigPathMap represents configurations on all types of problem daemons:
+// 1) Each key represents a type of problem daemon.
+// 2) Each value represents the config file paths to that type of problem daemon.
+type ProblemDaemonConfigPathMap map[ProblemDaemonType]*[]string
+
+// ProblemDaemonHandler represents the initialization handler for a type problem daemon.
+type ProblemDaemonHandler struct {
+	// CreateProblemDaemonOrDie initializes a problem daemon, panic if error occurs.
+	CreateProblemDaemonOrDie func(string) Monitor
+	// CmdOptionDescription explains how to configure the problem daemon from command line arguments.
+	CmdOptionDescription string
+}