Fluent Bit on Kubernetes

Fluent Bit is a lightweight and extensible Log Processor that comes with full support for Kubernetes:

  • Read Kubernetes/Docker log files from the file system or through Systemd Journal.
  • Enrich logs with Kubernetes metadata.
  • Deliver logs to third party storage services like Elasticsearch, InfluxDB, HTTP, etc.

Content:

Concepts

Before to get started is important to understand how Fluent Bit will be deployed. Kubernetes manage a cluster of nodes, so our log agent tool will need to run on every node to collect logs from every POD, for 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 these 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://github.com/fluent/fluent-bit-kubernetes-logging/blob/master/output/elasticsearch/fluent-bit-configmap.yaml

Fluent Bit to Elasticsearch

Fluent Bit DaemonSet ready to be used with Elasticsearch on a normal Kubernetes Cluster:

$ kubectl create -f https://github.com/fluent/fluent-bit-kubernetes-logging/blob/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://github.com/fluent/fluent-bit-kubernetes-logging/blob/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 enrigh 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.

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