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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
.
kubectl apply -f headless-service.yaml
where the file headless-service.yaml
contains the configuration shown above.
Create a StatefulSet
For a 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: 1
periodSeconds: 5
volumeMounts:
- name: rqlite-file
mountPath: /rqlite/file
volumeClaimTemplates:
- metadata:
name: rqlite-file
spec:
accessModes: [ "ReadWriteOnce" ]
storageClassName: "standard"
resources:
requests:
storage: 1Gi
Apply this configuration to your Kubernetes system, and a 3-node rqlite cluster will be created.
kubectl apply -f stateful-set.yaml
where the file stateful-set.yaml
contains the configuration shown above.
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 reducing the replicas
value, you also need to explicitly remove the deprovisioned nodes, or the Leader will continually attempt to contact those nodes.
⚠️ Be careful that you don't reduce the replica count such that there is no longer a quorum of nodes available. If you do this you will render your cluster unusable, and need to perform a manual recovery. The manual recovery process is fully documented.