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A Practical Guide to Kubernetes

Using hostPath Volume Type to Inject Configuration Files

Explore how to inject configuration files into Kubernetes pods using the hostPath volume type. Learn to deploy Prometheus with customized settings by mounting host files, manage configuration updates safely, and troubleshoot common issues with Minikube environments.

We'll cover the following...

Using Prometheus

We are about to deploy Prometheus for the first time. We won’t go into details about the application except that it’s best for your monitoring and alerting needs. We’ll use it only to demonstrate a few Kubernetes concepts. We won’t try to learn how to operate it here.

Looking into the definition

Let’s look at the application’s definition:

YAML
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: prometheus
  annotations:
    kubernetes.io/ingress.class: "nginx"
    ingress.kubernetes.io/ssl-redirect: "false"
    nginx.ingress.kubernetes.io/ssl-redirect: "false"
spec:
  rules:
  - http:
      paths:
      - path: /prometheus
        pathType: ImplementationSpecific
        backend:
          service:
            name: prometheus
            port:
              number: 9090
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: prometheus
spec:
  selector:
    matchLabels:
      type: monitor
      service: prometheus
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        type: monitor
        service: prometheus
    spec:
      containers:
      - name: prometheus
        image: prom/prometheus:v2.0.0
        command:
        - /bin/prometheus
        args:
        - "--config.file=/etc/prometheus/prometheus.yml"
        - "--storage.tsdb.path=/prometheus"
        - "--web.console.libraries=/usr/share"
        - "--web.external-url=http://192.168.99.100/prometheus"
---
apiVersion: v1
kind: Service
metadata:
  name: prometheus
spec:
  ports:
  - port: 9090
  selector:
    type: monitor
    service: prometheus

There’s nothing genuinely new in that YAML file. It defines an Ingress, a Deployment, and a Service. There is, however, one thing we might need to change.

Configuring the IP

Prometheus needs a full external URL if we want to change the base path. For practicing on our platform, the URL is set to Educative at line 49 in the following definition of `prometheus.yml.

YAML
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: prometheus
  annotations:
    kubernetes.io/ingress.class: "nginx"
    ingress.kubernetes.io/ssl-redirect: "false"
    nginx.ingress.kubernetes.io/ssl-redirect: "false"
spec:
  rules:
  - http:
      paths:
      - path: /prometheus
        pathType: ImplementationSpecific
        backend:
          service:
            name: prometheus
            port:
              number: 9090
---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: prometheus
spec:
  selector:
    matchLabels:
      type: monitor
      service: prometheus
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        type: monitor
        service: prometheus
    spec:
      containers:
      - name: prometheus
        image: prom/prometheus:v2.0.0
        command:
        - /bin/prometheus
        args:
        - "--config.file=/etc/prometheus/prometheus.yml"
        - "--storage.tsdb.path=/prometheus"
        - "--web.console.libraries=/usr/share"
        - "--web.external-url={{EDUCATIVE_LIVE_VM_URL}}/prometheus"
---
apiVersion: v1
kind: Service
metadata:
  name: prometheus
spec:
  ports:
  - port: 9090
  selector:
    type: monitor
    service: prometheus

Now that the URL is updated, let's create deployments:

Shell
kubectl create -f prometheus.yml
kubectl rollout status deploy prometheus

Once we created the application, we used the kubectl rollout status command to confirm that the deployment finished.

Testing Prometheus

Now, we can ...