How to Install Prometheus on Kubernetes and Use It for Monitoring

Introduction

Prometheus is an open-source instrumentation framework that can absorb massive amounts of data every second. This property makes Prometheus well-suited for monitoring complex workloads.

Use Prometheus to monitor your servers, VMs, databases, and draw on that data to analyze the performance of your applications and infrastructure.

This article explains how to install and set up Prometheus monitoring in a Kubernetes cluster.

Prerequisites

• A Kubernetes cluster
• A fully configured kubectl command-line interface on your local machine

Install Prometheus Monitoring on Kubernetes

Prometheus monitoring can be installed on a Kubernetes cluster by using a set of YAML (Yet Another Markup Language) files. These files contain configurations, permissions, and services that allow Prometheus to access resources and pull information by scraping the elements of your cluster.

YAML files are easily tracked, edited, and can be reused indefinitely.

Step 1: Create Monitoring Namespace

All the resources in Kubernetes are started in a namespace. Unless one is specified, the system uses the default namespace. To have better control over the cluster monitoring process, specify a monitoring namespace.

The name of the namespace needs to be a label compatible with DNS. For easy reference, we are going to name the namespace: monitoring.

There are two ways to create a monitoring namespace for retrieving metrics from the Kubernetes API.

Option 1:

Enter this simple command in your command-line interface and create the monitoring namespace on your host:

kubectl create namespace monitoring

The output confirms the namespace creation.

Option 2:

1. Create and apply a .yml file:

apiVersion: v1
kind: Namespace
metadata:
  name: monitoring

This method is convenient as you can deploy the same file in future instances.

2. Apply the file to your cluster by entering the following command in your command terminal:

kubectl -f apply namespace monitoring.yml

3. List existing namespaces by using this command:

kubectl get ns

Step 2: Create Persistent Volume and Persistent Volume Claim

A Prometheus deployment needs dedicated storage space to store scraping data. A practical way to fulfill this requirement is to connect the Prometheus deployment to an NFS volume. The following is a procedure for creating an NFS volume for Prometheus and including it in the deployment via persistent volumes.

1. Install the NFS server on your main system.

sudo apt install nfs-kernel-server

2. Create a directory to use with Prometheus.

sudo mkdir -p /mnt/nfs/promdata

3. Change the ownership of the directory.

sudo chown nobody:nogroup /mnt/nfs/promdata

4. Change the permissions for the directory.

sudo chmod 777 /mnt/nfs/promdata

5. Create a .yaml file using a text editor, such as nano:

nano pv-pvc.yaml

6. Paste the following configuration into the file. Adjust the parameters to fit your system. The spec.nfs.server field should correspond to the IP address of the system you installed NFS on.

apiVersion: v1

kind: PersistentVolume

metadata:

  name: pv-nfs-data

  namespace: monitoring

  labels:

    type: nfs

    app: prometheus-deployment

spec:

  storageClassName: managed-nfs

  capacity:

    storage: 1Gi

  accessModes:

    - ReadWriteMany

  nfs:

    server: 192.168.49.1

    path: "/mnt/nfs/promdata"

---

apiVersion: v1

kind: PersistentVolumeClaim

metadata:

  name: pvc-nfs-data

  namespace: monitoring

  labels:

    app: prometheus-deployment

spec:

  storageClassName: managed-nfs

  accessModes:

    - ReadWriteMany

  resources:

    requests:

      storage: 500Mi

Save the file and exit.

7. Apply the configuration with kubectl.

kubectl apply -f pv-pvc.yaml

Step 3: Create Cluster Role, Service Account and Cluster Role Binding

Namespaces are designed to limit the permissions of default roles. Hence, if we want to retrieve cluster-wide data, we need to give Prometheus access to all cluster resources.

The steps below explain how to create and apply a basic set of .yaml files that provide Prometheus with cluster-wide access.

1. Create a file for the cluster role definition.

nano cluster-role.yaml

2. Copy the following configuration and adjust it according to your needs. The verbs on each rule define the actions the role can take on the apiGroups.

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: prometheus
rules:
- apiGroups: [""]
  resources:
  - nodes
  - services
  - endpoints
  - pods
  verbs: ["get", "list", "watch"]
- apiGroups:
  - extensions
  resources:
  - ingresses
  verbs: ["get", "list", "watch"]

Save the file and exit.

3. Apply the file.

kubectl apply -f cluster-role.yaml

4. Create a service account file.

nano service-account.yaml

5. Copy the configuration below to define a service account.

apiVersion: v1
kind: ServiceAccount
metadata:
  name: prometheus
  namespace: monitoring

Save the file and exit.

6. Apply the file.

kubectl apply -f service-account.yaml

7. Create another file in a text editor:

nano cluster-role-binding.yaml

8. Define ClusterRoleBinding. This action is going to bind the Service Account to the previously-created Cluster Role.

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: prometheus
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: prometheus
subjects:
- kind: ServiceAccount
  name: prometheus
  namespace: monitoring

Save the file and exit.

9. Finally, apply the binding with kubectl.

kubectl apply -f cluster-role-binding.yaml

By adding these resources to our file, we have granted Prometheus cluster-wide access from the monitoring namespace.

Step 4: Create Prometheus ConfigMap

This section of the file provides instructions for the scraping process. Specific instructions for each element of the Kubernetes cluster should be customized to match individual monitoring requirements and cluster setup.

The example in this article uses a simple ConfigMap that defines the scrape and evaluation intervals, jobs, and targets.

1. Create the file in a text editor.

nano configmap.yaml

2. Copy the configuration below.

apiVersion: v1
kind: ConfigMap
metadata:
  name: prometheus-config
  namespace: monitoring
data:
  prometheus.yml: |
    global:
      scrape_interval:     15s
      evaluation_interval: 15s
    alerting:
      alertmanagers:
      - static_configs:
        - targets:
    rule_files:
      # - "example-file.yml"
    scrape_configs:
      - job_name: 'prometheus'
        static_configs:
        - targets: ['localhost:9090']

Save the file and exit.

3. Apply the ConfigMap with kubectl.

kubectl apply -f configmap.yaml

While the configuration presented above is sufficient to create a test Prometheus deployment, ConfigMaps usually provide further configuration details. The following sections discuss some additional options that you can include in the file.

Scrape Node

This service discovery exposes the nodes that make up your Kubernetes cluster. The kubelet runs on every single node and is a source of valuable information.

Scrape kubelet

    scrape_configs:
    - job_name: 'kubelet'
      kubernetes_sd_configs:
      - role: node
      scheme: https
      tls_config:
        ca_file: /var/run/secrets/kubernetes.io/serviceaccount/ca.crt
        insecure_skip_verify: true  # Required with Minikube.

Scrape cAdvisor (container level information)

The kubelet only provides information about itself and not the containers. To receive information from the container level, we need to use an exporter. The cAdvisor is already embedded and only needs a metrics_path: /metrics/cadvisor for Prometheus to collect container data:

    - job_name: 'cadvisor'
      kubernetes_sd_configs:
      - role: node
      scheme: https
      tls_config:
        ca_file: /var/run/secrets/kubernetes.io/serviceaccount/ca.crt
        insecure_skip_verify: true  # Required with Minikube.
      metrics_path: /metrics/cadvisor

Scrape APIServer

Use the endpoints role to target each application instance. This section of the file allows you to scrape API servers in your Kubernetes cluster.

    - job_name: 'k8apiserver'
      kubernetes_sd_configs:
      - role: endpoints
      scheme: https
      tls_config:
        ca_file: /var/run/secrets/kubernetes.io/serviceaccount/ca.crt
        insecure_skip_verify: true  # Required if using Minikube.
      bearer_token_file: /var/run/secrets/kubernetes.io/serviceaccount/token
      relabel_configs:
   - source_labels: [__meta_kubernetes_namespace, __meta_kubernetes_service_name, __meta_kubernetes_endpoint_port_name]
        action: keep
        regex: default;kubernetes;https

Scrape Pods for Kubernetes Services (excluding API Servers)

Scrape the pods backing all Kubernetes services and disregard the API server metrics.

- job_name: 'k8services'
      kubernetes_sd_configs:
      - role: endpoints
      relabel_configs:
      - source_labels:
          - __meta_kubernetes_namespace
          - __meta_kubernetes_service_name
        action: drop
        regex: default;kubernetes
      - source_labels:
          - __meta_kubernetes_namespace
        regex: default
        action: keep
      - source_labels: [__meta_kubernetes_service_name]
        target_label: job

Pod Role

Discover all pod ports with the name metrics by using the container name as the job label.

- job_name: 'k8pods'
      kubernetes_sd_configs:
      - role: pod
      relabel_configs:
      - source_labels: [__meta_kubernetes_pod_container_port_name]
        regex: metrics
        action: keep
      - source_labels: [__meta_kubernetes_pod_container_name]
        target_label: job

Step 5: Create Prometheus Deployment File

The deployment .yaml defines the number of replicas and templates to be applied to the defined set of pods. The file also connects the elements defined in the previous files, such as PV and PVC.

1. Create a file to store the deployment configuration.

nano deployment.yaml

2. Copy the following example configuration and adjust it according to your needs.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: prometheus
  namespace: monitoring
  labels:
    app: prometheus
spec:
  replicas: 1
  strategy:
    rollingUpdate:
      maxSurge: 1
      maxUnavailable: 1
    type: RollingUpdate
  selector:
    matchLabels:
      app: prometheus
  template:
    metadata:
      labels:
        app: prometheus
      annotations:
        prometheus.io/scrape: "true"
        prometheus.io/port: "9090"
    spec:
      containers:
      - name: prometheus
        image: prom/prometheus
        args:
          - '--storage.tsdb.retention=6h'
          - '--storage.tsdb.path=/prometheus'
          - '--config.file=/etc/prometheus/prometheus.yml'
        ports:
        - name: web
          containerPort: 9090
        volumeMounts:
        - name: prometheus-config-volume
          mountPath: /etc/prometheus
        - name: prometheus-storage-volume
          mountPath: /prometheus
      restartPolicy: Always

      volumes:
      - name: prometheus-config-volume
        configMap:
            defaultMode: 420
            name: prometheus-config

      - name: prometheus-storage-volume
        persistentVolumeClaim:
            claimName: pvc-nfs-data

Save and exit.

3. Deploy Prometheus with the following command.

kubectl apply -f deployment.yaml

Step 6: Create Prometheus Service

Prometheus is currently running in the cluster. Follow the procedure to create a service and obtain access to the data Prometheus has collected:

1. Create a .yaml to store service-related data.

nano service.yaml

2. Define the service in the file.

apiVersion: v1
kind: Service
metadata:
    name: prometheus-service
    namespace: monitoring
    annotations:
        prometheus.io/scrape: 'true'
        prometheus.io/port:   '9090'

spec:
    selector:
        app: prometheus
    type: NodePort
    ports:
    - port: 8080
      targetPort: 9090 
      nodePort: 30909

Save the file and exit.

3. Create the service with kubectl apply.

kubectl apply -f service.yaml

Monitoring Kubernetes Cluster with Prometheus

Prometheus is a pull-based system. It sends an HTTP request, a so-called scrape, based on the configuration defined in the deployment file. The response to this scrape request is stored and parsed in storage along with the metrics for the scrape itself.

The storage is a custom database on the Prometheus server and can handle a massive influx of data. It is possible to monitor thousands of machines simultaneously with a single Prometheus server.

The data needs to be appropriately exposed and formatted so that Prometheus can collect it. Prometheus can access data directly from the app’s client libraries or by using exporters.

Exporters are used for data that you do not have full control over (for example, kernel metrics). An exporter is a piece of software placed next to the application. Its purpose is to accept HTTP requests from Prometheus, make sure the data is in a supported format, and then provide the requested data to the Prometheus server.

Once you equip your applications to provide data to Prometheus, you need to inform Prometheus where to look for that data. Prometheus discovers targets to scrape from by using Service Discovery.

A Kubernetes cluster already has labels and annotations and an excellent mechanism for keeping track of changes and the status of its elements. Hence, Prometheus uses the Kubernetes API to discover targets.

The Kubernetes service discoveries that you can expose to Prometheus are:

• node
• endpoint
• service
• pod
• ingress

Prometheus retrieves machine-level metrics separately from the application information. The only way to expose memory, disk space, CPU usage, and bandwidth metrics is to use a node exporter. Additionally, metrics about cgroups need to be exposed as well.

Fortunately, the cAdvisor exporter is already embedded on the Kubernetes node level and can be readily exposed.

Once the system collects the data, you can access it by using the PromQL query language, export it to graphical interfaces like Grafana, or use it to send alerts with the Alertmanager.

Access Prometheus Monitoring

Ensure that all the relevant elements run properly in the monitoring namespace:

kubectl get all -n monitoring

Use the individual node URL and the nodePort defined in the service.yaml file to access Prometheus from your browser. For example:

http://192.153.99.106:30909

By entering the URL or IP of your node, and by specifying the port from the .yaml file, you have successfully gained access to Prometheus Monitoring.

How to Monitor kube-state-metrics? (Optional)

You are now able to fully monitor your Kubernetes infrastructure, as well as your application instances. However, this does not include metrics on the information Kubernetes has about the resources in your cluster.

The kube-state-metrics is an exporter that allows Prometheus to scrape that information as well.

1. Create a YAML file for the kube-state-metrics exporter:

---
apiVersion: apps/v1beta2
kind: Deployment
metadata:
  name: kube-state-metrics
spec:
  selector:
    matchLabels:
      app: kube-state-metrics
  replicas: 1
  template:
    metadata:
      labels:
        app: kube-state-metrics
    spec:
      serviceAccountName: prometheus
      containers:
      - name: kube-state-metrics
        image: quay.io/coreos/kube-state-metrics:v1.2.0
        ports:
        - containerPort: 8080
          name: monitoring
---
kind: Service
apiVersion: v1
metadata:
  name: kube-state-metrics
spec:
  selector:
    app: kube-state-metrics
  type: LoadBalancer
  ports:
  - protocol: TCP
    port: 8080
    targetPort: 8080

2. Apply the file by entering the following command:

kubectl apply -f kube-state-metrics.yml

Once you apply the file, access Prometheus by entering the node IP/URL and defined nodePort as previously defined.

Conclusion

Now that you have successfully installed Prometheus Monitoring on a Kubernetes cluster, you can track the overall health, performance, and behavior of your system.

No matter how large and complex your operations are, a metrics-based monitoring system such as Prometheus is a vital DevOps tool for maintaining a distributed microservices-based architecture.