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77 lines
3.4 KiB
Markdown
77 lines
3.4 KiB
Markdown
# Running rqlite on Kubernetes
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This document provides an example of how to run rqlite as a Kubernetes [StatefulSet](https://kubernetes.io/docs/concepts/workloads/controllers/statefulset/).
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## Creating a cluster
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### Create a Headless Service
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The first thing to do is to create a [Kubernetes _Headless Service_](https://kubernetes.io/docs/concepts/services-networking/service/#headless-services). The Headless service creates the required DNS entries, which allows the rqlite nodes to find each other, and automatically bootstrap a new cluster.
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```yaml
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apiVersion: v1
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kind: Service
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metadata:
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name: rqlite-svc
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spec:
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clusterIP: None
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selector:
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app: rqlite
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ports:
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- protocol: TCP
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port: 4001
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targetPort: 4001
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```
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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`.
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### Create a StatefulSet
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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.
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```yaml
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apiVersion: apps/v1
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kind: StatefulSet
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metadata:
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name: rqlite
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spec:
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selector:
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matchLabels:
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app: rqlite # has to match .spec.template.metadata.labels
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serviceName: rqlite-svc
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replicas: 3 # by default is 1
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template:
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metadata:
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labels:
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app: rqlite # has to match .spec.selector.matchLabels
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spec:
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terminationGracePeriodSeconds: 10
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containers:
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- name: rqlite
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image: rqlite/rqlite
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args: ["-disco-mode=dns","-disco-config={\"name\":\"rqlite-svc\"}","-bootstrap-expect","3"]
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ports:
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- containerPort: 4001
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name: rqlite
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readinessProbe:
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httpGet:
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scheme: HTTP
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path: /readyz?noleader
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port: 4001
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initialDelaySeconds: 1
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periodSeconds: 5
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volumeMounts:
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- name: rqlite-file
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mountPath: /rqlite/file
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volumeClaimTemplates:
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- metadata:
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name: rqlite-file
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spec:
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accessModes: [ "ReadWriteOnce" ]
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storageClassName: "standard"
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resources:
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requests:
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storage: 1Gi
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```
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Apply this configuration to your Kubernetes system, and a 3-node rqlite cluster will be created.
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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.
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## Scaling the cluster
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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](https://github.com/rqlite/rqlite/blob/master/DOC/CLUSTER_MGMT.md#removing-or-replacing-a-node) the deprovisioned nodes, or the Leader will continually attempt to contact those nodes.
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> :warning: **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](https://github.com/rqlite/rqlite/blob/master/DOC/CLUSTER_MGMT.md#dealing-with-failure).
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