EFK (Elasticsearch + Fluentd + Kibana) 是kubernetes官方推荐的日志收集方案，我们一起了解一下fluentd是如何收集kubernetes集群日志的，庆祝一下fluentd从 CNCF 毕业。开始之前，希望你已经读过Docker 容器日志分析, 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)区分，后一个EFK一般是原生部署。
CNCF , 全称Cloud Native Computing Foundation（云原生计算基金会），kubernetes也是其旗下，或者说大多数容器云项目都是其旗下。
部署EFK
k8s中部署efk，所用的yaml文件在 github.com/kubernetes/… ，你可以使用文章附录提供的脚本进行下载。
下载完成后执行 cd fluentd-elasticsearch && kubectl apply -f . 命令进行部署。
检查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
检查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>
这里我们知道了fluentd是以daemonset方式运行的，es和kibana是service方式。
注意 elasticsearch 默认部署文件是没有持久化的，如果需要持久化，需要调整其PVC设置。
fluentd 功能分析
1.查看fluentd的类型，没什么好说的
apiVersion: apps/v1 kind: DaemonSet metadata: name: fluentd-es-v2.2.1 namespace: kube-system
2.查看fluentd日志收集
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
这里可以清晰的看到，fluentd以daemonset方式运作，然后把系统的 /var/lib/docker/containers 挂载，这个目录我们在Docker 容器日志分析中介绍过，这是docker容器日志存放路径, 这样fluentd就完成了对容器默认日志的读取。
fluentd的配置文件是以configmap形式加载，继续往下看看。
3.收集容器日志配置
收集容器日志主要在 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>
细心的你会发现挂载的容器目录是 /var/lib/docker/containers ，日志应该都在这里，但是配置的监听的目录却是 /var/log/containers 。官方贴心的给出了注释，主要内容如下:
# 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 #
4.日志上传到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>
这里注意一下其中的host和port，均是elasticsearch service中定义的，如果修改过需要保持一致。fluentd也支持日志数据上传到外部的elasticsearch，也就是前文的elk/efk原生。
附录
1.架构图
2.下载脚本文件 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
3.参考链接:
