fluentd收集kubernetes 叢集日誌分析

EFK (Elasticsearch + Fluentd + Kibana) 是kubernetes官方推薦的日誌收集方案，我們一起了解一下fluentd是如何收集kubernetes叢集日誌的，慶祝一下fluentd從 CNCF 畢業。開始之前，希望你已經讀過Docker 容器日誌分析, 本文是其延生的第二篇。

注意 需要和ELK(Elasticsearch + Logstash + Kibana) 以及EFK(Elasticsearch + Filebeat + Kibana)區分，後一個EFK一般是原生部署。

CNCF , 全稱Cloud Native Computing Foundation（雲原生計算基金會），kubernetes也是其旗下，或者說大多數容器雲專案都是其旗下。

部署EFK

k8s中部署efk，所用的yaml檔案在 github.com/kubernetes/… ，你可以使用文章附錄提供的指令碼進行下載。

下載完成後執行 cd fluentd-elasticsearch && kubectl apply -f . 命令進行部署。

檢查elasticsearch和kibana service:

$ kubectl get svc -n kube-system
NAME                    TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)          AGE
elasticsearch-logging   NodePort    10.97.248.209    <none>        9200:32126/TCP   23d
kibana-logging          ClusterIP   10.103.126.183   <none>        5601/TCP         23d
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檢查fluentd DaemonSet:

$ kubectl get ds -n kube-system
NAME                    DESIRED   CURRENT   READY   UP-TO-DATE   AVAILABLE   NODE SELECTOR                   AGE
fluentd-es-v2.4.0       2         2         2       2            2           <none>                          23d
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這裡我們知道了fluentd是以daemonset方式執行的，es和kibana是service方式。

注意 elasticsearch 預設部署檔案是沒有持久化的，如果需要持久化，需要調整其PVC設定。

fluentd 功能分析

1. 檢視fluentd的型別，沒什麼好說的

   apiVersion: apps/v1
   kind: DaemonSet
   metadata:
     name: fluentd-es-v2.2.1
     namespace: kube-system
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2. 檢視fluentd日誌收集

   containers:
   - name: fluentd-es
   image: k8s.gcr.io/fluentd-elasticsearch:v2.2.0
   
   ...
   
   volumeMounts:
   - name: varlog
     mountPath: /var/log
   - name: varlibdockercontainers
     mountPath: /var/lib/docker/containers
     readOnly: true
   - name: config-volume
     mountPath: /etc/fluent/config.d
   
   ...
   
   volumes:
   - name: varlog
   hostPath:
     path: /var/log
   - name: varlibdockercontainers
   hostPath:
     path: /var/lib/docker/containers
   - name: config-volume
   configMap:
     name: fluentd-es-config-v0.1.6
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   這裡可以清晰的看到，fluentd以daemonset方式運作，然後把系統的 /var/lib/docker/containers 掛載，這個目錄我們在Docker 容器日誌分析中介紹過，這是docker容器日誌存放路徑, 這樣fluentd就完成了對容器預設日誌的讀取。

   fluentd的配置檔案是以configmap形式載入，繼續往下看看。

3. 收集容器日誌配置

   收集容器日誌主要在 containers.input.conf，如下:

   <source>
     @id fluentd-containers.log
     @type tail
     path /var/log/containers/*.log
     pos_file /var/log/es-containers.log.pos
     tag raw.kubernetes.*
     read_from_head true
     <parse>
       @type multi_format
       <pattern>
         format json
         time_key time
         time_format %Y-%m-%dT%H:%M:%S.%NZ
       </pattern>
       <pattern>
         format /^(?<time>.+) (?<stream>stdout|stderr) [^ ]* (?<log>.*)$/
         time_format %Y-%m-%dT%H:%M:%S.%N%:z
       </pattern>
     </parse>
   </source>
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   細心的你會發現掛載的容器目錄是 /var/lib/docker/containers ，日誌應該都在這裡，但是配置的監聽的目錄卻是 /var/log/containers 。官方貼心的給出了註釋，主要內容如下:

    # Example
       # =======
       # ...
       #
       # The Kubernetes fluentd plugin is used to write the Kubernetes metadata to the log
       # record & add labels to the log record if properly configured. This enables users
       # to filter & search logs on any metadata.
       # For example a Docker container's logs might be in the directory:
       #
       #  /var/lib/docker/containers/997599971ee6366d4a5920d25b79286ad45ff37a74494f262e3bc98d909d0a7b
       #
       # and in the file:
       #
       #  997599971ee6366d4a5920d25b79286ad45ff37a74494f262e3bc98d909d0a7b-json.log
       #
       # where 997599971ee6... is the Docker ID of the running container.
       # The Kubernetes kubelet makes a symbolic link to this file on the host machine
       # in the /var/log/containers directory which includes the pod name and the Kubernetes
       # container name:
       #
       #    synthetic-logger-0.25lps-pod_default_synth-lgr-997599971ee6366d4a5920d25b79286ad45ff37a74494f262e3bc98d909d0a7b.log
       #    ->
       #    /var/lib/docker/containers/997599971ee6366d4a5920d25b79286ad45ff37a74494f262e3bc98d909d0a7b/997599971ee6366d4a5920d25b79286ad45ff37a74494f262e3bc98d909d0a7b-json.log
       #
       # The /var/log directory on the host is mapped to the /var/log directory in the container
       # running this instance of Fluentd and we end up collecting the file:
       #
       #   /var/log/containers/synthetic-logger-0.25lps-pod_default_synth-lgr-997599971ee6366d4a5920d25b79286ad45ff37a74494f262e3bc98d909d0a7b.log
       #
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4. 日誌上傳到elasticsearch

   output.conf: |-
       <match **>
         @id elasticsearch
         @type elasticsearch
         @log_level info
         type_name _doc
         include_tag_key true
         host elasticsearch-logging
         port 9200
         logstash_format true
         <buffer>
           @type file
           path /var/log/fluentd-buffers/kubernetes.system.buffer
           flush_mode interval
           retry_type exponential_backoff
           flush_thread_count 2
           flush_interval 5s
           retry_forever
           retry_max_interval 30
           chunk_limit_size 2M
           queue_limit_length 8
           overflow_action block
         </buffer>
       </match>
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   這裡注意一下其中的host和port，均是elasticsearch service中定義的，如果修改過需要保持一致。fluentd也支援日誌資料上傳到外部的elasticsearch，也就是前文的elk/efk原生。

附錄

1. 架構圖

2. 下載指令碼檔案 download.sh

   for file in es-service es-statefulset fluentd-es-configmap fluentd-es-ds kibana-deployment kibana-service; do curl -o $file.yaml https://raw.githubusercontent.com/kubernetes/kubernetes/master/cluster/addons/fluentd-elasticsearch/$file.yaml; done
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3. 參考連結:

   • kubernetes.io/docs/concep…

   • kubernetes.io/docs/tasks/…

   • 恭喜 Fluentd 從 CNCF 畢業