fix(metricprovider): respect --logformat json for metric plugin process logger

go.mod

@@ -19,6 +19,7 @@ require (
 	github.com/golang/protobuf v1.5.4
 	github.com/google/uuid v1.6.0
 	github.com/grpc-ecosystem/grpc-gateway v1.16.0
+	github.com/hashicorp/go-hclog v1.6.3
 	github.com/hashicorp/go-plugin v1.8.0
 	github.com/influxdata/influxdb-client-go/v2 v2.14.0
 	github.com/juju/ansiterm v1.0.0
@@ -125,7 +126,6 @@ require (
 	github.com/gregdel/pushover v1.3.1 // indirect
 	github.com/gregjones/httpcache v0.0.0-20190611155906-901d90724c79 // indirect
 	github.com/hashicorp/go-cleanhttp v0.5.2 // indirect
-	github.com/hashicorp/go-hclog v1.6.3 // indirect
 	github.com/hashicorp/go-retryablehttp v0.7.7 // indirect
 	github.com/hashicorp/yamux v0.1.2 // indirect
 	github.com/huandu/xstrings v1.5.0 // indirect

metricproviders/plugin/client/client.go

@@ -2,10 +2,13 @@ package client
 
 import (
 	"fmt"
+	"io"
 	"os/exec"
 	"sync"
 
+	"github.com/hashicorp/go-hclog"
 	goPlugin "github.com/hashicorp/go-plugin"
+	log "github.com/sirupsen/logrus"
 
 	"github.com/argoproj/argo-rollouts/metricproviders/plugin/rpc"
 	"github.com/argoproj/argo-rollouts/pkg/apis/rollouts/v1alpha1"
@@ -68,6 +71,7 @@ func (m *metricPlugin) startPluginSystem(metric v1alpha1.Metric) (rpc.MetricProv
 				Plugins:         pluginMap,
 				Cmd:             exec.Command(pluginPath, args...),
 				Managed:         true,
+				Logger:          newPluginLogger(),
 			})
 
 			rpcClient, err := m.pluginClient[pluginName].Client()
@@ -108,3 +112,27 @@ func (m *metricPlugin) startPluginSystem(metric v1alpha1.Metric) (rpc.MetricProv
 
 	return nil, fmt.Errorf("no plugin found")
 }
+
+// newPluginLogger builds the hclog.Logger used for the go-plugin client's own log output
+// (handshake/lifecycle logs, and the plugin process's stderr relay). By default go-plugin
+// falls back to its own unstructured text logger whenever ClientConfig.Logger is nil, which
+// is inconsistent with the controller's own logs when the controller is run with
+// `--logformat json`: every other component's logs are JSON, but metric plugin logs remain
+// plain text. When the controller's standard logger is configured for JSON output, mirror
+// that here so the plugin logger's output is JSON too. Returns nil (go-plugin's own default
+// logger) in every other case, preserving prior behavior exactly.
+func newPluginLogger() hclog.Logger {
+	return newPluginLoggerWithOutput(hclog.DefaultOutput)
+}
+
+func newPluginLoggerWithOutput(w io.Writer) hclog.Logger {
+	if _, ok := log.StandardLogger().Formatter.(*log.JSONFormatter); !ok {
+		return nil
+	}
+	return hclog.New(&hclog.LoggerOptions{
+		Output:     w,
+		Level:      hclog.Trace,
+		Name:       "plugin",
+		JSONFormat: true,
+	})
+}

metricproviders/plugin/client/client_test.go

@@ -0,0 +1,41 @@
+package client
+
+import (
+	"bytes"
+	"encoding/json"
+	"testing"
+
+	log "github.com/sirupsen/logrus"
+	"github.com/stretchr/testify/assert"
+)
+
+// TestNewPluginLoggerRespectsControllerLogFormat verifies that the go-plugin client's own
+// logger mirrors the controller's configured log format. Before this fix, the plugin
+// client's Logger field was always left unset, so go-plugin always fell back to its
+// unstructured, hardcoded-text default logger regardless of the controller's own
+// `--logformat json` setting.
+func TestNewPluginLoggerRespectsControllerLogFormat(t *testing.T) {
+	origFormatter := log.StandardLogger().Formatter
+	defer log.StandardLogger().SetFormatter(origFormatter)
+
+	t.Run("default text logformat leaves go-plugin's own default logger untouched", func(t *testing.T) {
+		log.StandardLogger().SetFormatter(&log.TextFormatter{})
+		logger := newPluginLogger()
+		assert.Nil(t, logger, "expected nil so go-plugin falls back to its own default logger")
+	})
+
+	t.Run("json logformat produces a JSON plugin logger", func(t *testing.T) {
+		log.StandardLogger().SetFormatter(&log.JSONFormatter{})
+
+		var buf bytes.Buffer
+		logger := newPluginLoggerWithOutput(&buf)
+		assert.NotNil(t, logger)
+
+		logger.Info("plugin log line", "plugin", "my-plugin")
+
+		var parsed map[string]any
+		err := json.Unmarshal(buf.Bytes(), &parsed)
+		assert.NoError(t, err, "expected the plugin logger to emit a single JSON object, got: %s", buf.String())
+		assert.Equal(t, "plugin log line", parsed["@message"])
+	})
+}