server: Use default logging configuration instead of zap production one

This fixes problem where logs json changes format of timestamp.

tests/e2e/cluster_test.go

@@ -175,6 +175,7 @@ type etcdProcessClusterConfig struct {
 	v2deprecation       string
 
 	rollingStart bool
+	logLevel     string
 }
 
 // newEtcdProcessCluster launches a new cluster from etcd processes, returning
@@ -315,6 +316,10 @@ func (cfg *etcdProcessClusterConfig) etcdServerProcessConfigs(tb testing.TB) []*
 			args = append(args, "--v2-deprecation", cfg.v2deprecation)
 		}
 
+		if cfg.logLevel != "" {
+			args = append(args, "--log-level", cfg.logLevel)
+		}
+
 		etcdCfgs[i] = &etcdServerProcessConfig{
 			lg:           lg,
 			execPath:     cfg.execPath,

tests/e2e/zap_logging_test.go

@@ -0,0 +1,76 @@
+// Copyright 2022 The etcd Authors
+//
+// 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.
+
+//go:build !cov
+// +build !cov
+
+package e2e
+
+import (
+	"encoding/json"
+	"testing"
+	"time"
+)
+
+func TestServerJsonLogging(t *testing.T) {
+	BeforeTest(t)
+
+	epc, err := newEtcdProcessCluster(t, &etcdProcessClusterConfig{
+		clusterSize:  1,
+		initialToken: "new",
+		logLevel:     "debug",
+	})
+	if err != nil {
+		t.Fatalf("could not start etcd process cluster (%v)", err)
+	}
+	logs := epc.procs[0].Logs()
+	time.Sleep(time.Second)
+	if err = epc.Close(); err != nil {
+		t.Fatalf("error closing etcd processes (%v)", err)
+	}
+	var entry logEntry
+	lines := logs.Lines()
+	if len(lines) == 0 {
+		t.Errorf("Expected at least one log line")
+	}
+	for _, line := range lines {
+		err := json.Unmarshal([]byte(line), &entry)
+		if err != nil {
+			t.Errorf("Failed to parse log line as json, err: %q, line: %s", err, line)
+			continue
+		}
+		if entry.Level == "" {
+			t.Errorf(`Missing "level" key, line: %s`, line)
+		}
+		if entry.Timestamp == "" {
+			t.Errorf(`Missing "ts" key, line: %s`, line)
+		}
+		if _, err := time.Parse("2006-01-02T15:04:05.000Z0700", entry.Timestamp); entry.Timestamp != "" && err != nil {
+			t.Errorf(`Unexpected "ts" key format, err: %s`, err)
+		}
+		if entry.Caller == "" {
+			t.Errorf(`Missing "caller" key, line: %s`, line)
+		}
+		if entry.Message == "" {
+			t.Errorf(`Missing "message" key, line: %s`, line)
+		}
+	}
+}
+
+type logEntry struct {
+	Level     string `json:"level"`
+	Timestamp string `json:"ts"`
+	Caller    string `json:"caller"`
+	Message   string `json:"msg"`
+}