The other day I faced a scenario, wherein I wanted to output logs to Elastic Stack (previously called ELK Stack) for visualization through dashboards. Elastic Stack comprises three software components: Elasticsearch, Logstash, and Kibana. When combined, they offer advanced logging, alerting, and searching [1]. The logging was needed so I could dig deeper into what was happening with an application running on a Kubernetes cluster over a prolonged period of time.

I turned to Elastic Stack because it became uber-popular as ELK Stack for good reason. It's widely adopted, helps speed up the process of analyzing massive amounts of data that's churned out by machines, and is sometimes used in enterprises as an alternative to one of the commercial market leaders, Splunk [2].

To make sure I could use my solution as hoped, I decided to create a lab before trying it out elsewhere in a more critical environment. In this article, I show the steps I took and the resulting proof-of-concept functionality.

Three Is the Magic Number

I'm going to use the excellent K3s to build my Kubernetes cluster. For instructions on how to install K3s, check out the "Teeny, Tiny" section in my article on StatusBay in this issue. However, I would definitely recommend getting some background information by visiting their site [3] or reading another of my articles [4] in which I use it for applications in the Internet of Things (IoT) space.

If, when you run the command

$ kubectl get pods --all-namespaces

you see CrashLoopBackOff errors, it's likely to do with netfilter's iptables tying itself in knots.

Kubernetes is well known for causing consternation with other software that uses iptables. I talk more about this in the IoT article, but you can check which chains are loaded in iptables with:

$ iptables -nvL

Consider stopping firewalld if it's running; try the command

$ systemctl status firewalld

and replace status with stop to halt the service, if required.

On my Linux Mint 19 (Tara) machine, which sits atop Ubuntu 18.04 (Bionic), I had to uninstall K3s (use the /usr/local/bin/k3s-uninstall.sh script), switch off Uncomplicated Firewall (UFW) and use the desktop GUI to clear my iptables clashes before running the installation command again. It took no time at all, but obviously it's a far from ideal situation.

In my lab environment, however, I didn't mind. Clearly you should ensure this part is working more gracefully and as expected before deploying it in production. Incidentally, once the core Kubernetes pods were all up and running, I could switch UFW back on with impunity.

A happy K3s installation with all its relevant pods running looks like Listing 1, with the core K3s pods running without error. From the second command in the listing, you can see that only the K3s server is running.

echo ~ $ kubectl get pods --all-namespaces
NAMESPACE     NAME                                      READY   STATUS      RESTARTS   AGE
kube-system   metrics-server-6d684c7b5-ssck9            1/1     Running     0          12m
kube-system   local-path-provisioner-58fb86bdfd-hgdc4   1/1     Running     0          12m
kube-system   helm-install-traefik-2b2f2                0/1     Completed   0          12m
kube-system   svclb-traefik-p46m5                       2/2     Running     0          11m
kube-system   coredns-d798c9dd-kjhjv                    1/1     Running     0          12m
kube-system   traefik-6787cddb4b-594kr                  1/1     Running     0          11m
$ kubectl get nodes
NAME   STATUS   ROLES    AGE   VERSION
echo   Ready    master   20m   v1.17.3+k3s1

The machine's hostname for the K3s server is echo , which you would need to know to add worker nodes (agents, in K3s parlance), for which the ROLES column would state <none> .

A Moose Loose

Thanks to K3s, you now have a highly scalable Kubernetes build available. You would need to plug in agent nodes for load balancing and failover to create a proper cluster, as I discussed in the "Kubernetes k3s lightweight distro" IoT article mentioned earlier.

That's not a problem in this example, however. To install the Elastic Stack, I'll use the excellent Kubernetes package manager Helm. I give complete instructions in the StatusBay article "Dig Deep into Kubernetes" in this issue (just ignore the first paragraph on installing StatusBay and the second listing in that article). You'll also find some nice, clear docs on the Helm installation page [5].

From version 3.0 onward, Helm had some relatively significant changes with the removal of Tiller because of security concerns [6], so be sure to choose version 3.0+.

Hoots Mon

The Helm Project itself provides the code to install Elasticsearch, Logstash, and Kibana on its GitHub page [7]. To begin, you have to add the repository to Helm so it knows where to look for the charts (or packages) wanted; then, before installing any charts, always check for the latest versions before submitting a search to discover the massive list of available Helm charts:

$ helm repo add stable https://kubernetes-charts.storage.googleapis.com/
$ helm repo update
$ helm search repo stable

If you're new to Helm, have a look at the values.yaml file, where you can customize the Helm chart so it's easier to install with the options you need for your requirements, yet still take advantage of easier revision control between upgrades and downgrades. You can check out an example values file with adjustable options in a browser [8].

To see the dependency information on the elastic-stack Helm chart, enter:

$ helm show chart stable/elastic-stack

Listing 2 shows the output and helpfully lists all the packages referenced in the elastic-stack chart. As you can see, Helm takes care of a lot of behind-the-scenes configuration for you automatically, which is why Helm is so powerful. You can change a few variables to suit your needs and, with revision control and other features, keep a close track on how your Kubernetes packages are installed.

$ helm show chart stable/elastic-stack
apiVersion: v1
appVersion: "6"
dependencies:
- condition: elasticsearch.enabled
  name: elasticsearch
  repository: https://kubernetes-charts.storage.googleapis.com/
  version: ^1.32.0
- condition: kibana.enabled
  name: kibana
  repository: https://kubernetes-charts.storage.googleapis.com/
  version: ^3.2.0
- condition: filebeat.enabled
  name: filebeat
  repository: https://kubernetes-charts.storage.googleapis.com/
  version: ^1.7.0
- condition: logstash.enabled
  name: logstash
  repository: https://kubernetes-charts.storage.googleapis.com/
  version: ^2.3.0
- condition: fluentd.enabled
  name: fluentd
  repository: https://kubernetes-charts.storage.googleapis.com/
  version: ^2.2.0
- condition: fluent-bit.enabled
  name: fluent-bit
  repository: https://kubernetes-charts.storage.googleapis.com/
  version: ^2.8.0
- condition: fluentd-elasticsearch.enabled
  name: fluentd-elasticsearch
  repository: https://kubernetes-charts.storage.googleapis.com/
  version: ^2.0.0
- condition: nginx-ldapauth-proxy.enabled
  name: nginx-ldapauth-proxy
  repository: https://kubernetes-charts.storage.googleapis.com/
  version: ^0.1.0
- condition: elasticsearch-curator.enabled
  name: elasticsearch-curator
  repository: https://kubernetes-charts.storage.googleapis.com/
  version: ^2.1.0
- condition: elasticsearch-exporter.enabled
  name: elasticsearch-exporter
  repository: https://kubernetes-charts.storage.googleapis.com/
  version: ^2.1.0
description: A Helm chart for ELK
home: https://www.elastic.co/products
icon: https://www.elastic.co/assets/bltb35193323e8f1770/logo-elastic-stack-lt.svg
maintainers:
- email: pete.brown@powerhrg.com
  name: rendhalver
- email: jrodgers@powerhrg.com
  name: jar361
- email: christian.roggia@gmail.com
  name: christian-roggia
name: elastic-stack
version: 1.9.0