[Failed to Retrieve Secrets Following Vault Server Failover in Kubernetes High-Availability Cluster][Permission Denied]

I trust this message finds you in good health. I am reaching out to provide insights into a recent incident involving our HashiCorp Vault deployment on our Kubernetes cluster.
We currently run three Vault nodes, consisting of one leader and two followers. An unexpected event occurred recently when node 2 automatically transitioned to become the leader of the cluster. Subsequently, applications encountered difficulties fetching secrets from the Vault server, resulting in permission denied errors.
After a thorough investigation and several hours of research and development, I successfully resolved the issue by reconfiguring the Kubernetes authentication for Vault using the command **vault write auth/kubernetes/config** .
It’s crucial for us to understand why this occurred and, more importantly, how we can prevent such incidents in the future. Given the critical nature of our production applications that rely on Vault, it is imperative to establish measures to avoid similar disruptions. This is the second time we are facing this issue and unable to find the actual reason behind this. Could anybody suggest the actual root cause of this. Thanks in advance.

vault-agent-init log:
2024-01-04T08:24:06.219Z [ERROR] agent.auth.handler: error authenticating:
| Error making API request.
| URL: PUT http://x.x.svc:8200/v1/auth/kubernetes/login
| Code: 403. Errors:
| * permission denied
2024-01-04T08:24:07.220Z [INFO] agent.auth.handler: authenticating

vaules.yaml for vault helm chart:
GOOGLE_REGION: $some_value
GOOGLE_PROJECT: $some_value


  • type: ‘secret’
    name: ‘$some_value’
    enabled: true

Size of the PVC created

size: $some_value
enabled: true
replicas: 3
enabled: true
config: |
ui = true

storage "raft" {
  path = "/vault/data"

listener "tcp" {
address     = ""
cluster_addr  = ""
tls_disable = "true"
seal "gcpckms" {
  credentials = "$some_value"
  project = "$some_value"
  region = "$some_value"
  key_ring = "$some_value"
  crypto_key = "$some_value"

Used this for k8s auth policy.
vault write auth/kubernetes/config
token_reviewer_jwt="(cat /var/run/secrets/kubernetes.io/serviceaccount/token)" \ kubernetes_host=https://{KUBERNETES_PORT_443_TCP_ADDR}:443

This issue has been fixed. Please configure auth method as stated below.

Use local service account token as the reviewer JWT

When running Vault in a Kubernetes pod the recommended option is to use the pod’s local service account token. Vault will periodically re-read the file to support short-lived tokens. To use the local token and CA certificate, omit token_reviewer_jwt and kubernetes_ca_cert when configuring the auth method. Vault will attempt to load them from token and ca.crt respectively inside the default mount folder /var/run/secrets/kubernetes.io/serviceaccount/.

vault write auth/kubernetes/config \

Note: Requires Vault 1.9.3+. In earlier versions the service account token and CA certificate is read once and stored in Vault storage. When the service account token expires or is revoked, Vault will no longer be able to use the TokenReview API and client authentication will fail.