A node is a worker machine in Kubernetes, previously known as a minion. A node may be a VM or physical machine, depending on the cluster. Each node has the services necessary to run pods and is managed by the master components...
A pod (as in a pod of whales or pea pod) is a group of one or more containers (such as Docker containers), the shared storage for those containers, and options about how to run the containers. Pods are always co-located and co-scheduled, and run in a shared context...
A DaemonSet ensures that all (or some) nodes run a copy of a pod. As nodes are added to the cluster, pods are added to them. As nodes are removed from the cluster, those pods are garbage collected. Deleting a DaemonSet will clean up the pods it created...
Since applications runs in Pods and multiple Pods might exists across multiple nodes, we need a specific Fluentd-Pod that takes care of log collection on each node: Fluentd DaemonSet.
Fluentd DaemonSet
For Kubernetes, a DaemonSet ensures that all (or some) nodes run a copy of a pod. To solve log collection, we are going to implement a Fluentd DaemonSet.
Fluentd is flexible enough and has the proper plugins to distribute logs to different third-party applications like databases or cloud services, so the principal question is Where will the logs be stored?. Once we got that question answered, we can move forward configuring our DaemonSet.
The following steps will focus on sending the logs to an Elasticsearch Pod:
Get Fluentd DaemonSet sources
We have created a Fluentd DaemonSet that have the proper rules and container image ready to get started:
The cloned repository contains several configurations that allow to deploy Fluentd as a DaemonSet. The Docker container image distributed on the repository also comes pre-configured so that Fluentd can gather all the logs from the Kubernetes node's environment and append the proper metadata to the logs.
This repository has several presets for Alpine/Debian with popular outputs:
This YAML file contains two relevant environment variables that are used by Fluentd when the container starts:
Environment Variable
Description
Default
FLUENT_ELASTICSEARCH_HOST
Specify the host name or IP address.
elasticsearch-logging
FLUENT_ELASTICSEARCH_PORT
Elasticsearch TCP port
9200
FLUENT_ELASTICSEARCH_SSL_VERIFY
Whether verify SSL certificates or not.
true
FLUENT_ELASTICSEARCH_SSL_VERSION
Specify the version of TLS.
TLSv1_2
Any relevant change needs to be done in the YAML file before deployment. The defaults assume that at least one Elasticsearch Pod elasticsearch-logging exists in the cluster.