Kubernetes service registration

Kubernetes Service Registration tags Vault pods with their current status for use with selectors. Service registration is only available when Vault is running in High Availability mode.

HashiCorp Supported – Kubernetes Service Registration is officially supported by HashiCorp.

Configuration

service_registration "kubernetes" {
  namespace      = "my-namespace"
  pod_name       = "my-pod-name"
}

Alternatively, the namespace and pod name can be set through the following environment variables:

This allows you to set these parameters using the Downward API.

If using only environment variables, the service registration stanza declaring you're using Kubernetes must still exist to indicate your intentions:

service_registration "kubernetes" {}

For service registration to succeed, Vault must be able to apply labels to pods in Kubernetes. The following RBAC rules are required to allow the service account associated with the Vault pods to update its own pod specification:

kind: Role
apiVersion: rbac.authorization.k8s.io/v1
metadata:
  namespace: mynamespace
  name: vault-service-account
rules:
- apiGroups: [""]
  resources: ["pods"]
  verbs: ["get", "update", "patch"]

Examples

Once properly configured, enabling service registration will cause Kubernetes pods to come up with the following labels:

apiVersion: v1
kind: Pod
metadata:
  name: vault
  labels:
    vault-active: "false"
    vault-initialized: "true"
    vault-perf-standby: "false"
    vault-sealed: "false"
    vault-version: 1.18.1

After shutdowns, Vault pods will bear the following labels:

apiVersion: v1
kind: Pod
metadata:
  name: vault
  labels:
    vault-active: "false"
    vault-initialized: "false"
    vault-perf-standby: "false"
    vault-sealed: "true"
    vault-version: 1.18.1

Label definitions

vault-active (string: "true"/"false") – Vault active is updated dynamically each time Vault's active status changes. True indicates that this Vault pod is currently the leader. False indicates that this Vault pod is currently a standby.
vault-initialized (string: "true"/"false") – Vault initialized is updated dynamically each time Vault's initialization status changes. True indicates that Vault is currently initialized. False indicates the Vault is currently uninitialized.
vault-perf-standby (string: "true"/"false") – Vault performance standby is updated dynamically each time Vault's leader/standby status changes. This field is only valuable if the pod is a member of a performance standby cluster, it will simply be set to "false" when it's not applicable. True indicates that this Vault pod is currently a performance standby. False indicates that this Vault pod is currently a performance leader.
vault-sealed (string: "true"/"false") – Vault sealed is updated dynamically each time Vault's sealed/unsealed status changes. True indicates that Vault is currently sealed. False indicates that Vault is currently unsealed.
vault-version (string: "1.18.1") – Vault version is a string that will not change during a pod's lifecycle.

Working with vault's service discovery labels

Example service

With labels applied to the pod, services can be created using selectors to filter pods with specific Vault HA roles, effectively allowing direct communication with subsets of Vault pods. Note the vault-active: "true" line below.

apiVersion: v1
kind: Service
metadata:
  labels:
    app.kubernetes.io/instance: vault
    app.kubernetes.io/name: vault
    helm.sh/chart: vault-0.29.0
  name: vault-active-us-east
  namespace: default
spec:
  clusterIP: 10.7.254.51
  ports:
  - name: http
    port: 8200
    protocol: TCP
    targetPort: 8200
  - name: internal
    port: 8201
    protocol: TCP
    targetPort: 8201
  publishNotReadyAddresses: false
  selector:
    app.kubernetes.io/instance: vault
    app.kubernetes.io/name: vault
    component: server
    vault-active: "true"
  type: ClusterIP

Also, by setting publishNotReadyAddresses: false above, pods that have failed will be removed from the service pool.

With this active service in place, we now have a dedicated endpoint that will always reach the active node. When setting up Vault replication, it can be used as the primary address:

$ vault write -f sys/replication/performance/primary/enable \
    primary_cluster_addr='https://vault-active-us-east:8201'

Example upgrades

In conjunction with the pod labels and the OnDelete upgrade strategy, upgrades are much easier to orchestrate:

$ helm upgrade vault --set='server.image.tag=1.18.1'

$ kubectl delete pod --selector=vault-active=false \
    --selector=vault-version=1.2.3

$ kubectl delete pod --selector=vault-active=true \
    --selector=vault-version=1.2.3

When deleting an instance of a pod, the StatefulSet defining the desired state of the cluster will reschedule the deleted pods with the newest image.