Monitoraggio Kubernetes con Prometheus esterno al kube

Il monitoraggio di cluster Kubernetes automatizzato con un Prometheus esterno al kube

Kubernetes

Il [Kubernetes] (o k8s) è una piattaforma self-healing e opensource per l’automazione dei deploy, l’orchestrazione dinamica e la gestione delle applicazioni nei container.

Tutto il progetto Kubernetes ha abbracciato la tecnologia Prometheus e quindi offre supporto al relativo protocollo per il monitoraggio sui servizi presenti nella suite k8s con tanto di alert e generazione automatica di pannelli con grafici (CPU, Rete,…​) che diventano fondamentali per evitare interruzioni e analizzare disservizi in genere.

Diverse modalità di monitoraggio

Il montoraggio del cluster può essere effettuato tramite tipologie diverse di architetture:

  • tramite il [Prometheus Operator] (progetto Opensource della CoreOs) interno al k8s

  • tramite un Prometheus esterno al cluster k8s che si integra con il Service Discovery del k8s

In questo articolo ci occupermo della seconda ipotesi, il monitoraggio tramite un Prometheus esterno al k8s.

Prerequisiti del k8s per il monitoraggio dall’esterno

Ma come può il mio Prometheus accedere alle metriche dei Pod e dei Container?

Grazie all’integrazione tra Prometheus è k8s è possibile prelevare le metriche del cluster utilizzando l’API del k8s, le API fanno da proxy verso le metriche esposte automaticamente all’interno del cluster dai pod e dal cAdvisor.

Affinchè questa integrazione funzioni è necessario che l’API del Kubernetes sia abilitata all’utenticazione tramite auth token e che il cAdvisor sia abilitato all’interno del cluster. Ma andiamo per gradi.

cAdvisor

cAdvisor is an open source container resource usage and performance analysis agent. It is purpose-built for containers and supports Docker containers natively. In Kubernetes, cAdvisor is integrated into the Kubelet binary. cAdvisor auto-discovers all containers in the machine and collects CPU, memory, filesystem, and network usage statistics. cAdvisor also provides the overall machine usage by analyzing the ‘root’ container on the machine.

Enable auth token & cAdvisor in k8s

Note

[…​] the kubelet uses token authentication and authorization, as otherwise Prometheus needs a client certificate, which gives it full access to the kubelet, rather than just the metrics. Token authentication and authorization allows more fine grained and easier access control.

This means the kubelet configuration must contain these flags:

  • —authentication-token-webhook=true This flag enables, that a ServiceAccount token can be used to authenticate against the kubelet(s).

  • —authorization-mode=Webhook This flag enables, that the kubelet will perform an RBAC request with the API to determine, whether the requesting entity (Prometheus in this case) is allow to access a resource, in specific for this project the /metrics endpoint.

Kubelet is a systemd service running on the Kubernetes master and on each of the Kubernetes nodes. As of version 1.10, kubeadm configures the kubelet service via command line arguments defined in /etc/systemd/system/kubelet.service.d/10-kubeadm.conf.

As shown in the kube-prometheus-on-kubeadm documentation, we need two changes:

  • Remove the cadvisor-port=0 flag in order to enable the cadvisor.

  • Add the —authentication-token-webhook=true flag.

Instead of modifying the file 10-kubeadm.conf, we create a new file 11-kube-prometheus.conf. These files are applied in alphabetical order, so settings in the our file will overwrite the original settings from 10-kubeadm.conf.

Our 11-kube-prometheus.conf file looks like this:

[Service]
# Remove the cadvisor-port=0 setting to expose the cadvisor metrics
Environment="KUBELET_CADVISOR_ARGS="
# allow webhook token authentication.
Environment="KUBELET_AUTH_TOKEN_WEBHOOK=--authentication-token-webhook=true --authorization-mode=Webhook"
ExecStart=
ExecStart=/usr/bin/kubelet $KUBELET_KUBECONFIG_ARGS $KUBELET_SYSTEM_PODS_ARGS $KUBELET_NETWORK_ARGS $KUBELET_DNS_ARGS $KUBELET_AUTH_TOKEN_WEBHOOK $KUBELET_AUTHZ_ARGS $KUBELET_CGROUP_ARGS $KUBELET_CADVISOR_ARGS $KUBELET_CERTIFICATE_ARGS $KUBELET_EXTRA_ARGS

Note that in order to override ExecStart, we first need to make it empty and then re-define it. Otherwise we would just be adding an additional command instead of replacing the command.

Avvio del servizio Prometheus esterno al k8s

Come sempre noi consigliamo di gestire il [Prometheus] esterno tramite [Docker] in modo da semplificarne la configurazione e la sua gestione nel tempo.

docker-compose.yml
version: '3'

services:

  prometheus:
    image: prom/prometheus:v2.5.0
    container_name: prometheus
    ports:
      - 9090:9090
    restart: always
    user: '1000'
    volumes:
        - "$PWD/promdata:/prometheus"
        - "$PWD/promconf:/etc/prometheus:ro"
    command: "--config.file=/etc/prometheus/prometheus.yml --storage.tsdb.retention=90d"
    logging:
      driver: "json-file"
      options:
        max-size: "200k"
        max-file: "10"

Configurazione del Prometheus per utilizzare il Service Discovery k8s

prometheus.yml
global:
  scrape_interval:     15s
  evaluation_interval: 15s
  external_labels:
    monitor: 'SkyTv'

rule_files:
  - '/etc/prometheus/prometheus.rules'

scrape_configs:
- job_name: 'kubernetes-apiservers'

  kubernetes_sd_configs:
    - role: endpoints
      api_server: https://kubernetes.default.svc
      tls_config:
        ca_file: /etc/prometheus/ca.crt
      bearer_token_file: /etc/prometheus/kube-api-token

  scheme: https

  tls_config:
    ca_file: /etc/prometheus/ca.crt
  bearer_token_file: /etc/prometheus/kube-api-token
  relabel_configs:
  - source_labels: [__meta_kubernetes_namespace, __meta_kubernetes_service_name, __meta_kubernetes_endpoint_port_name]
    action: keep
    regex: default;kubernetes;https

- job_name: 'kubernetes-nodes'

  scheme: https

  tls_config:
    ca_file: /etc/prometheus/ca.crt
  bearer_token_file: /etc/prometheus/kube-api-token

  kubernetes_sd_configs:
    - role: node
      api_server: https://kubernetes.default.svc
      tls_config:
        ca_file: /etc/prometheus/ca.crt
      bearer_token_file: /etc/prometheus/kube-api-token

  relabel_configs:
  - action: labelmap
    regex: __meta_kubernetes_node_label_(.+)
  - target_label: __address__
    replacement: kubernetes.default.svc
  - source_labels: [__meta_kubernetes_node_name]
    regex: (.+)
    target_label: __metrics_path__
    replacement: /api/v1/nodes/${1}/proxy/metrics

- job_name: 'kubernetes-cadvisor'

  scheme: https

  tls_config:
    ca_file: /etc/prometheus/ca.crt
  bearer_token_file: /etc/prometheus/kube-api-token

  kubernetes_sd_configs:
    - role: node
      api_server: https://kubernetes.default.svc
      tls_config:
        ca_file: /etc/prometheus/ca.crt
      bearer_token_file: /etc/prometheus/kube-api-token

  relabel_configs:
  - action: labelmap
    regex: __meta_kubernetes_node_label_(.+)
  - target_label: __address__
    replacement: kubernetes.default.svc
  - source_labels: [__meta_kubernetes_node_name]
    regex: (.+)
    target_label: __metrics_path__
    replacement: /api/v1/nodes/${1}/proxy/metrics/cadvisor

Installare il Grafana

docker-compose.yml
version: '3'

services:

  grafana:
    image: grafana/grafana:5.3.2
    container_name: grafana
    ports:
     - 3000:3000
    restart: always
    volumes:
      - "$PWD/data:/var/lib/grafana"
    user: '1000'
    environment:
      GF_SMTP_ENABLED: 'false'

Esempi di grafici Grafana

Esempio di grafici da Kubernetes
Grafana & Kubernetes

References

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