Create 8.4.manage-running-logs.md (#2000)

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docs-2.0/nebula-operator/8.custom-cluster-configurations/8.4.manage-running-logs.md

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+# Manage cluster logs
+
+Running logs of NebulaGraph cluster services (graphd, metad, storaged) are generated and stored in the `/usr/local/nebula/logs` directory of each service container by default.
+
+## View logs
+
+To view the running logs of a NebulaGraph cluster, you can use the `kubectl logs` command. 
+
+For example, to view the running logs of the Storage service:
+
+```bash
+// View the name of the Storage service Pod, nebula-storaged-0.
+$ kubectl get pods
+NAME                               READY   STATUS    RESTARTS      AGE
+nebula-exporter-84b6974497-cr54d   1/1     Running   0             43h
+nebula-graphd-0                    1/1     Running   0             22h
+nebula-metad-0                     1/1     Running   0             45h
+nebula-storaged-0                  1/1     Running   0             45h
+...
+
+// Enter the container storaged of the Storage service.
+$ kubectl exec -it nebula-storaged-0 -c storaged -- /bin/bash
+
+// View the running logs of the Storage service.
+$ cd /usr/local/nebula/logs
+```
+
+## Clean logs
+
+Running logs generated by cluster services during runtime will occupy disk space. To avoid occupying too much disk space, the Operator uses a sidecar container to periodically clean and archive logs.
+
+To facilitate log collection and management, each NebulaGraph service deploys a sidecar container responsible for collecting logs generated by the service container and sending them to the specified log disk. The sidecar container automatically cleans and archives logs using the [logrotate](https://linux.die.net/man/8/logrotate) tool.
+
+In the YAML configuration file of the cluster instance, you can configure log rotation to automatically clean and archive logs through the `spec.logRotate` field. By default, the log rotation feature is turned off. Here is an example of enabling log rotation:
+
+```yaml
+...
+spec:
+  graphd:
+    config:
+      # Whether to include a timestamp in the log file name. "true" means yes, "false" means no. 
+      "timestamp_in_logfile_name": "false"
+  metad:
+    config:
+      "timestamp_in_logfile_name": "false"
+  storaged:
+    config:
+      "timestamp_in_logfile_name": "false"
+  logRotate: # Log rotation configuration
+    # The number of times a log file is rotated before being deleted. The default value is 5, and 0 means the log file will not be rotated before being deleted.
+    rotate: 5
+    # The log file is rotated only if it grows larger than the specified size. The default value is 200M.
+    size: "200M"
+```
+
+## Collect logs
+
+If you don't want to mount additional log disks to back up log files, or if you want to collect logs and send them to a log center using services like [fluent-bit](https://fluentbit.io/), you can configure logs to be output to standard error. The Operator uses the [glog](https://github.com/google/glog) tool to log to standard error output.
+
+!!! caution
+
+    Currently, NebulaGraph Operator only collects standard error logs.。
+
+In the YAML configuration file of the cluster instance, you can configure logging to standard error output in the `config` and `env` fields of each service.
+
+
+```yaml
+...
+spec:
+  graphd:
+    config:
+      # Whether to redirect standard error to a separate output file. The default value is false, which means it is not redirected.
+      redirect_stdout: "false"
+      # The severity level of log content: INFO, WARNING, ERROR, and FATAL. The corresponding values are 0, 1, 2, and 3.
+      stderrthreshold: "0"
+    env: 
+    - name: GLOG_logtostderr # Write log to standard error output instead of a separate file.
+      value: "1" # 1 represents writing to standard error output, and 0 represents writing to a file.
+    image: vesoft/nebula-graphd
+    replicas: 1
+    resources:
+      requests:
+        cpu: 500m
+        memory: 500Mi
+    service:
+      externalTrafficPolicy: Local
+      type: NodePort
+    version: v{{nebula.release}}
+  metad:
+    config:
+      redirect_stdout: "false"
+      stderrthreshold: "0"
+    dataVolumeClaim:
+      resources:
+        requests:
+          storage: 1Gi
+      storageClassName: ebs-sc
+    env:
+    - name: GLOG_logtostderr
+      value: "1"
+    image: vesoft/nebula-metad
+  ...
+```