Kubernetes

Kubernetes Production Grade Log Processor
​Fluent Bit is a lightweight and extensible Log Processor that comes with full support for Kubernetes:
Process Kubernetes containers logs from the file system or Systemd/Journald.
Enrich logs with Kubernetes Metadata.
Centralize your logs in third party storage services like Elasticsearch, InfluxDB, HTTP, etc.
Concepts
Before getting started it is important to understand how Fluent Bit will be deployed. Kubernetes manages a cluster of nodes, so our log agent tool will need to run on every node to collect logs from every POD, hence Fluent Bit is deployed as a DaemonSet (a POD that runs on every node of the cluster).
When Fluent Bit runs, it will read, parse and filter the logs of every POD and will enrich each entry with the following information (metadata):
Pod Name
Pod ID
Container Name
Container ID
Labels
Annotations
To obtain this information, a built-in filter plugin called kubernetes talks to the Kubernetes API Server to retrieve relevant information such as the pod_id, labels and annotations, other fields such as pod_name, container_id and container_name are retrieved locally from the log file names. All of this is handled automatically, no intervention is required from a configuration aspect.
Our Kubernetes Filter plugin is fully inspired on the Fluentd Kubernetes Metadata Filter written by Jimmi Dyson.
Installation
​Fluent Bit must be deployed as a DaemonSet, so on that way it will be available on every node of your Kubernetes cluster. To get started run the following commands to create the namespace, service account and role setup:
$ kubectl create namespace logging
$ kubectl create -f https://raw.githubusercontent.com/fluent/fluent-bit-kubernetes-logging/master/fluent-bit-service-account.yaml
$ kubectl create -f https://raw.githubusercontent.com/fluent/fluent-bit-kubernetes-logging/master/fluent-bit-role.yaml
$ kubectl create -f https://raw.githubusercontent.com/fluent/fluent-bit-kubernetes-logging/master/fluent-bit-role-binding.yaml
The next step is to create a ConfigMap that will be used by our Fluent Bit DaemonSet:
$ kubectl create -f https://raw.githubusercontent.com/fluent/fluent-bit-kubernetes-logging/master/output/elasticsearch/fluent-bit-configmap.yaml
Note for Kubernetes < v1.16
For Kubernetes versions older than v1.16, the DaemonSet resource is not available on apps/v1 , the resource is available on apiVersion: extensions/v1beta1 . Our current Daemonset Yaml files uses the new apiVersion.
If you are using and older Kubernetes version, manually grab a copy of your Daemonset Yaml file and replace the value of apiVersion from:
apiVersion: apps/v1
to
apiVersion: extensions/v1beta1
You can read more about this deprecation on Kubernetes v1.14 Changelog here:
​https://github.com/kubernetes/kubernetes/blob/master/CHANGELOG-1.14.md#deprecations​
Fluent Bit to Elasticsearch
Fluent Bit DaemonSet ready to be used with Elasticsearch on a normal Kubernetes Cluster:
$ kubectl create -f https://raw.githubusercontent.com/fluent/fluent-bit-kubernetes-logging/master/output/elasticsearch/fluent-bit-ds.yaml
Fluent Bit to Elasticsearch on Minikube
If you are using Minikube for testing purposes, use the following alternative DaemonSet manifest:
$ kubectl create -f https://raw.githubusercontent.com/fluent/fluent-bit-kubernetes-logging/master/output/elasticsearch/fluent-bit-ds-minikube.yaml
Details
The default configuration of Fluent Bit makes sure of the following:
Consume all containers logs from the running Node.
The Tail input plugin will not append more than 5MB  into the engine until they are flushed to the Elasticsearch backend. This limit aims to provide a workaround for backpressure scenarios.
The Kubernetes filter will enrich the logs with Kubernetes metadata, specifically labels and annotations. The filter only goes to the API Server when it cannot find the cached info, otherwise it uses the cache.
The default backend in the configuration is Elasticsearch set by the Elasticsearch Ouput Plugin. It uses the Logstash format to ingest the logs. If you need a different Index and Type, please refer to the plugin option and do your own adjustments.
There is an option called Retry_Limit set to False, that means if Fluent Bit cannot flush the records to Elasticsearch it will re-try indefinitely until it succeed.
Windows Deployment
Since v1.5.0, Fluent Bit supports deployment to Windows pods.
Log files overview
When deploying Fluent Bit to Kubernetes, there are three log files that you need to pay attention to.
C:\k\kubelet.err.log
This is the error log file from kubelet daemon running on host.
You will need to retain this file for future troubleshooting (to debug deployment failures etc.)
C:\var\log\containers\<pod>_<namespace>_<container>-<docker>.log
This is the main log file you need to watch. Configure Fluent Bit to follow this file.
It is actually a symlink to the Docker log file in C:\ProgramData\, with some additional metadata on its file name.
C:\ProgramData\Docker\containers\<docker>\<docker>.log
This is the log file produced by Docker.
Normally you don't directly read from this file, but you need to make sure that this file is visible from Fluent Bit.
Typically, your deployment yaml contains the following volume configuration.
spec:
  containers:
  - name: fluent-bit
    image: my-repo/fluent-bit:1.5.0
    volumeMounts:
    - mountPath: C:\k
      name: k
    - mountPath: C:\var\log
      name: varlog
    - mountPath: C:\ProgramData
      name: progdata
  volumes:
  - name: k
    hostPath:
      path: C:\k
  - name: varlog
    hostPath:
      path: C:\var\log
  - name: progdata
    hostPath:
      path: C:\ProgramData
Configure Fluent Bit
Assuming the basic volume configuration described above, you can apply the following config to start logging.
fluent-bit.conf: |
    [SERVICE]
      Parsers_File      C:\\fluent-bit\\parsers.conf
​
    [INPUT]
      Name              tail
      Tag               kube.*
      Path              C:\\var\\log\\containers\\*.log
      Parser            docker
      DB                C:\\fluent-bit\\tail_docker.db
      Mem_Buf_Limit     7MB
      Refresh_Interval  10
​
    [INPUT]
      Name              tail
      Tag               kubelet.err
      Path              C:\\k\\kubelet.err.log
      DB                C:\\fluent-bit\\tail_kubelet.db
​
    [FILTER]
      Name              kubernetes
      Match             kube.*
      Kube_URL          https://kubernetes.default.svc.cluster.local:443
​
    [OUTPUT]
      Name  stdout
      Match *
​
parsers.conf: |
    [PARSER]
        Name         docker
        Format       json
        Time_Key     time
        Time_Format  %Y-%m-%dT%H:%M:%S.%L
        Time_Keep    On
Mitigate unstable network on Windows pods
Windows pods often lack working DNS immediately after boot (#78479). To mitigate this issue, filter_kubernetes provides a built-in mechanism to wait until the network starts up:
DNS_Retries - Retries N times until the network start working (6)
DNS_Wait_Time - Lookup interval between network status checks (30)
By default, Fluent Bit waits for 3 minutes (30 seconds x 6 times). If it's not enough for you, tweak the configuration as follows.
[filter]
    Name kubernetes
    ...
    DNS_Retries 10
    DNS_Wait_Time 30
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