fluidb-old/DOC/KUBERNETES.md

Running rqlite on Kubernetes

This document provides an example of how to run rqlite as a Kubernetes StatefulSet.

Creating a cluster

Create a Headless Service

The first thing to do is to create a Kubernetes Headless Service. The Headless service creates the required DNS entries, which allows the rqlite nodes to find each other, and automatically bootstrap a new cluster.

apiVersion: v1
kind: Service
metadata:
  name: rqlite-svc
spec:
  clusterIP: None 
  selector:
    app: rqlite
  ports:
    - protocol: TCP
      port: 4001
      targetPort: 4001

Apply the configuration above to your Kubernetes deployment. It will create a DNS entry rqlite-svc, which will resolve to the IP addresses of any Pods with the tag rqlite.

Create a StatefuiSet

For an rqlite cluster to function properly in a production environment, the rqlite nodes require a persistent network identifier and storage. This is what a StatefulSet can provide. The example belows shows you how to configure a 3-node rqlite cluster.

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: rqlite
spec:
  selector:
    matchLabels:
      app: rqlite # has to match .spec.template.metadata.labels
  serviceName: "rqlite-svc"
  replicas: 3 # by default is 1
  template:
    metadata:
      labels:
        app: rqlite # has to match .spec.selector.matchLabels
    spec:
      terminationGracePeriodSeconds: 10
      containers:
      - name: rqlite
        image: rqlite/rqlite
        args: ["-disco-mode=dns","-disco-config={\"name\":\"rqlite-svc\"}","-bootstrap-expect","3"]
        ports:
        - containerPort: 4001
          name: rqlite
        readinessProbe:
          httpGet:
            scheme: HTTP
            path: /readyz?noleader
            port: 4001
          initialDelaySeconds: 10
          periodSeconds: 5
        volumeMounts:
        - name: rqlite-file
          mountPath: /rqlite/file
  volumeClaimTemplates:
  - metadata:
      name: rqlite-file
    spec:
      accessModes: [ "ReadWriteOnce" ]
      storageClassName: "standard"
      resources:
        requests:
          storage: 1Gi

Note the args passed to rqlite. The arguments tell rqlite to use dns discovery mode, and to resolve the DNS name rqlite-svc to find the IP addresses of other nodes in the cluster. Furthermore it tells rqlite to wait until three nodes are available (counting itself as one of those nodes) before attempting to form a cluster.

Scaling the cluster

You can grow the cluster at anytime, simply by increasing the replica count. Shrinking the cluster, however, will require some manual intervention. As well change the replicas value, you also need to explicitly remove the deprovisioned nodes, or the Leader will continually attempt to contact those nodes.