Refactor CLI initialization (#562)

This cleans up the CLI code significantly.
Also makes some of this re-usable for providers who want to do so.

This also removes the main.go from the top of the tree of the repro,
instead moving it into cmd/virtual-kubelet.
This allows us to better utilize the package namespace (and e.g. mv the
`vkubelet` package to the top of the tree).

trace/opencensus/jaeger.go

@@ -0,0 +1,37 @@
+// +build !no_jaeger_exporter
+
+package opencensus
+
+import (
+	"errors"
+	"os"
+
+	"go.opencensus.io/exporter/jaeger"
+	"go.opencensus.io/trace"
+)
+
+func init() {
+	RegisterTracingExporter("jaeger", NewJaegerExporter)
+}
+
+// NewJaegerExporter creates a new opencensus tracing exporter.
+func NewJaegerExporter(opts TracingExporterOptions) (trace.Exporter, error) {
+	jOpts := jaeger.Options{
+		Endpoint:      os.Getenv("JAEGER_ENDPOINT"),
+		AgentEndpoint: os.Getenv("JAEGER_AGENT_ENDPOINT"),
+		Username:      os.Getenv("JAEGER_USER"),
+		Password:      os.Getenv("JAEGER_PASSWORD"),
+		Process: jaeger.Process{
+			ServiceName: opts.ServiceName,
+		},
+	}
+
+	if jOpts.Endpoint == "" && jOpts.AgentEndpoint == "" {
+		return nil, errors.New("Must specify either JAEGER_ENDPOINT or JAEGER_AGENT_ENDPOINT")
+	}
+
+	for k, v := range opts.Tags {
+		jOpts.Process.Tags = append(jOpts.Process.Tags, jaeger.StringTag(k, v))
+	}
+	return jaeger.NewExporter(jOpts)
+}

trace/opencensus/ocagent.go

@@ -0,0 +1,37 @@
+// +build !no_ocagent_exporter
+
+package opencensus
+
+import (
+	"os"
+
+	"contrib.go.opencensus.io/exporter/ocagent"
+	"github.com/cpuguy83/strongerrors"
+	"github.com/pkg/errors"
+	"go.opencensus.io/trace"
+)
+
+func init() {
+	RegisterTracingExporter("ocagent", NewOCAgentExporter)
+}
+
+// NewOCAgentExporter creates a new opencensus tracing exporter using the opencensus agent forwarder.
+func NewOCAgentExporter(opts TracingExporterOptions) (trace.Exporter, error) {
+	agentOpts := append([]ocagent.ExporterOption{}, ocagent.WithServiceName(opts.ServiceName))
+
+	if endpoint := os.Getenv("OCAGENT_ENDPOINT"); endpoint != "" {
+		agentOpts = append(agentOpts, ocagent.WithAddress(endpoint))
+	} else {
+		return nil, strongerrors.InvalidArgument(errors.New("must set endpoint address in OCAGENT_ENDPOINT"))
+	}
+
+	switch os.Getenv("OCAGENT_INSECURE") {
+	case "0", "no", "n", "off", "":
+	case "1", "yes", "y", "on":
+		agentOpts = append(agentOpts, ocagent.WithInsecure())
+	default:
+		return nil, strongerrors.InvalidArgument(errors.New("invalid value for OCAGENT_INSECURE"))
+	}
+
+	return ocagent.NewExporter(agentOpts...)
+}

trace/opencensus/register.go

@@ -0,0 +1,45 @@
+package opencensus
+
+import (
+	"github.com/cpuguy83/strongerrors"
+	"github.com/pkg/errors"
+	"go.opencensus.io/trace"
+)
+
+type TracingExporterOptions struct {
+	Tags        map[string]string
+	ServiceName string
+}
+
+var (
+	tracingExporters = make(map[string]TracingExporterInitFunc)
+)
+
+// TracingExporterInitFunc is the function that is called to initialize an exporter.
+// This is used when registering an exporter and called when a user specifed they want to use the exporter.
+type TracingExporterInitFunc func(TracingExporterOptions) (trace.Exporter, error)
+
+// RegisterTracingExporter registers a tracing exporter.
+// For a user to select an exporter, it must be registered here.
+func RegisterTracingExporter(name string, f TracingExporterInitFunc) {
+	tracingExporters[name] = f
+}
+
+// GetTracingExporter gets the specified tracing exporter passing in the options to the exporter init function.
+// For an exporter to be availbale here it must be registered with `RegisterTracingExporter`.
+func GetTracingExporter(name string, opts TracingExporterOptions) (trace.Exporter, error) {
+	f, ok := tracingExporters[name]
+	if !ok {
+		return nil, strongerrors.NotFound(errors.Errorf("tracing exporter %q not found", name))
+	}
+	return f(opts)
+}
+
+// AvailableTraceExporters gets the list of registered exporters
+func AvailableTraceExporters() []string {
+	out := make([]string, 0, len(tracingExporters))
+	for k := range tracingExporters {
+		out = append(out, k)
+	}
+	return out
+}

trace/opencensus/register_test.go

@@ -0,0 +1,45 @@
+package opencensus
+
+import (
+	"testing"
+
+	"github.com/cpuguy83/strongerrors"
+
+	"go.opencensus.io/trace"
+)
+
+func TestGetTracingExporter(t *testing.T) {
+	defer delete(tracingExporters, "mock")
+
+	mockExporterFn := func(_ TracingExporterOptions) (trace.Exporter, error) {
+		return nil, nil
+	}
+
+	_, err := GetTracingExporter("notexist", TracingExporterOptions{})
+	if !strongerrors.IsNotFound(err) {
+		t.Fatalf("expected not found error, got: %v", err)
+	}
+
+	RegisterTracingExporter("mock", mockExporterFn)
+
+	if _, err := GetTracingExporter("mock", TracingExporterOptions{}); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestAvailableExporters(t *testing.T) {
+	defer delete(tracingExporters, "mock")
+
+	mockExporterFn := func(_ TracingExporterOptions) (trace.Exporter, error) {
+		return nil, nil
+	}
+	RegisterTracingExporter("mock", mockExporterFn)
+
+	for _, e := range AvailableTraceExporters() {
+		if e == "mock" {
+			return
+		}
+	}
+
+	t.Fatal("could not find mock exporter in list of registered exporters")
+}