Defining Alert Rules

Installation of Prometheus #

We’ll continue the trend of using Helm as the installation mechanism. Prometheus's Helm Chart is maintained as one of the official Charts. You can find more info in the project’s README. If you focus on the variables in the Configuration section, you’ll notice that there are quite a few things we can tweak. We won’t go through all the variables. You can check the official documentation for that. Instead, we’ll start with a basic setup, and extend it as our needs increase.

Let’s take a look at the variables we’ll use as a start.

cat mon/prom-values-bare.yml

The output is as follows.

server:
  ingress:
    enabled: true
    annotations:
      ingress.kubernetes.io/ssl-redirect: "false"
      nginx.ingress.kubernetes.io/ssl-redirect: "false"
  resources:
    limits:
      cpu: 100m
      memory: 1000Mi
    requests:
      cpu: 10m
      memory: 500Mi
alertmanager:
  ingress:
    enabled: true
    annotations:
      ingress.kubernetes.io/ssl-redirect: "false"
      nginx.ingress.kubernetes.io/ssl-redirect: "false"
  resources:
    limits:
      cpu: 10m
      memory: 20Mi
    requests:
      cpu: 5m
      memory: 10Mi
kubeStateMetrics:
  resources:
    limits:
      cpu: 10m
      memory: 50Mi
    requests:
      cpu: 5m
      memory: 25Mi
nodeExporter:
  resources:
    limits:
      cpu: 10m
      memory: 20Mi
    requests:
      cpu: 5m
      memory: 10Mi
pushgateway:
  resources:
    limits:
      cpu: 10m
      memory: 20Mi
    requests:
      cpu: 5m
      memory: 10Mi

All we’re doing, for now, is defining resources for all five applications we’ll install and enabling Ingress with a few annotations that will make sure that we are not redirected to the HTTPS version since we do not have certificates for our ad-hoc domains. We’ll dive into the applications that’ll be installed later.

For now, we’ll define the addresses for Prometheus and Alertmanager UIs.

PROM_ADDR=mon.$LB_IP.nip.io

AM_ADDR=alertmanager.$LB_IP.nip.io

Let’s install the Chart.

kubectl create namespace metrics

helm install prometheus \
    stable/prometheus \
    --namespace metrics \
    --version 9.5.2 \
    --set server.ingress.hosts={$PROM_ADDR} \
    --set alertmanager.ingress.hosts={$AM_ADDR} \
    -f mon/prom-values-bare.yml

The command we just executed should be self-explanatory.

The Chart installed one DeamonSet and four Deployments.

The DeamonSet is a Node Exporter, and it’ll run a Pod on every node of the cluster. It provides node-specific metrics that will be pulled by Prometheus. The second exporter (Kube State Metrics) runs as a single replica Deployment. It fetches data from Kube API and transforms them into the Prometheus-friendly format. The two will provide most of the metrics we’ll need. Later on, we might choose to expand them with additional exporters. For now, those two together with metrics fetched directly from Kube API should provide more metrics than we can absorb in a single chapter.

Further on, we got the Server, which is Prometheus itself. Alertmanager will forward alerts to their destination. Finally, there is Pushgateway that we might explore in one of the following chapters.

While waiting for all those apps to become operational, we might explore the flow between them.

Flow of data to and from Prometheus #

Prometheus Server pulls data from exporters. In our case, those are Node Exporter and Kube State Metrics. The job of those exporters is to fetch data from the source and transform it into the Prometheus-friendly format. Node Exporter gets the data from /proc and /sys volumes mounted on the nodes, while Kube State Metrics gets it from Kube API. Metrics are stored internally in Prometheus.

Apart from being able to query that data, we can define alerts. When an alert reaches its threshold, it is forwarded to Alertmanager which acts as a crossroad. Depending on its internal rules, it can forward those alerts further to various destinations like Slack, email, and HipChat (only to name a few).

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