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Monitoring container clusters with Prometheus
Perfect Fit
Permanent or Volatile?
Before installing Prometheus, you should consider whether you want to install the software inside or outside the Kubernetes environment. An installation outside can open up many options for permanent data storage. Monitoring also works independent of the monitored system.
However, you can set up integration in Kubernetes far more easily; this applies to both the network and authentication. Thanks to persistent volumes [7] or stateful sets [8], Kubernetes has the option to keep data permanently. If you operate further external monitoring, you will likely combine Prometheus with Kubernetes.
Tested
To illustrate the information outlined above, I will demonstrate how you can run your own small Kubernetes cluster with a Prometheus extension based on Minikube [9]. Minikube offers the easiest way to test Kubernetes on your own computer, whether Linux, OS X, or Windows (Table 1). If you want to follow the steps, you will find an installation manual online [10]. The minikube start
command generates a new Kubernetes; depending on the base system, Minikube still requires VirtualBox or kubectl
to be in place.
Table 1
Useful Minikube Commands
Command | Effect |
---|---|
minikube dashboard
|
Opens the Kubernetes dashboard in the browser. |
minikube service --namespace = monitoring prometheus
|
Calls up the prometheus service in the browser.
|
minikube service --namespace = monitoring --url prometheus
|
Outputs the URL for the prometheus service.
|
Complete listings of the extracts shown in the article are available online [11], in particular, the YAML files with the Kubernetes definitions (*.yml
): Unpack them in a working directory to send them later to Kubernetes using kubectl
. Kubernetes internally stores the content generated from the YAML files and creates corresponding objects as namespaces, deployments, or services.
Because the following steps affect Minikube, I omit advanced topics such as persistent storage and role-based access (RBAC) [12], introduced in Kubernetes 1.6, that can be used with Prometheus.
Name Tag
Kubernetes uses namespaces to isolate the resources of individual users or a group of users from one another on a physical cluster. For the sample project, generate the monitoring
namespace:
kubectl create -f 01-monitoring-namespace.yml
If you simply want to understand what is happening in the small Kubernetes cluster, launch the administration interface with
minikube dashboard
then select the monitoring
namespace as shown in Figure 2.
The next step is then carried out by Prometheus. The software is available as an official Docker image [13], but without a configuration. To avoid having to build a new image for each change, pack the Kubernetes configuration as a prometheus.yml
data object in a ConfigMap [14] with the name prometheus-configmap
. You can then independently modify, delete, or create a new ConfigMap:
kubectl create -f 02-prometheus-configmap.yml
Deployments provide declarations [15] for updating pods and replica sets. The Kubernetes deployment for Prometheus (Listing 4) integrates the recently created ConfigMap as a new volume with the name prometheus volume-config
by means of a volume mount in the /etc/prometheus/prometheus.yml
path. This establishes a connection between Prometheus and its configuration:
kubectl create -f 03-prometheus-deployment.yml
Listing 4
03-prometheus-deployment.yml
apiVersion: apps/v1beta1 kind: Deployment metadata: labels: app: prometheus name: prometheus namespace: monitoring spec: replicas: 1 template: metadata: labels: app: prometheus spec: containers: - image: prom/prometheus:v1.7.1 name: prometheus args: - -config.file=/etc/prometheus/prometheus.yml - -storage.local.path=/prometheus ports: - containerPort: 9090 volumeMounts: - mountPath: /etc/prometheus name: prometheus-volume-config - mountPath: /prometheus name: prometheus-volume-data volumes: - name: prometheus-volume-config configMap: name: prometheus-configmap - emptyDir: {} name: prometheus-volume-data
You can configure the directory that stores the Prometheus database with volumes
, and more specifically as emptyDir
. It discards the data when you relaunch the Prometheus pod; you will want to use persistent volumes here for a production setup.
You are still missing an appropriate service for Prometheus to access the current Prometheus instance:
kubectl create -f 04-prometheus-service.yml
The service can then be called via kubectl
(Listing 5). At this point, note that Minikube sometimes displays services as pending
. Do not worry, they are still working.
Listing 5
Services in the monitoring Namespace
# kubectl get service --namespace=monitoring NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE prometheus 10.0.0.221 <pending> 9090:31244/TCP 1m
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