This guide will walk you through the process of setting up HashiCorp Vault to manage Kubernetes secrets using Helm.

• Kubernetes cluster
• Helm v3
• kubectl command-line tool

1. Add the HashiCorp Helm repository:

   helm repo add hashicorp https://helm.releases.hashicorp.com

2. Update the Helm repository:

   helm repo update

3. Install the Vault Helm chart:

   helm install vault hashicorp/vault

4. Initiate and unseal vault

   kubectl exec vault-0 -- vault operator init -key-shares=1 -key-threshold=1 -format=json > keys.json
   
   VAULT_UNSEAL_KEY=$(cat keys.json | jq -r ".unseal_keys_b64[]")
   echo $VAULT_UNSEAL_KEY
   
   VAULT_ROOT_KEY=$(cat keys.json | jq -r ".root_token")
   echo $VAULT_ROOT_KEY
   
   kubectl exec vault-0 -- vault operator unseal $VAULT_UNSEAL_KEY
   
   kubectl exec vault-0 -- vault login $VAULT_ROOT_KEY
   
   
   kubectl get pods
   

5. Create a service account for Vault:

   kubectl create serviceaccount vault-auth

6. Log in to the Vault pod:

   kubectl exec -it vault-0 -- /bin/sh

7. Enable the Kubernetes authentication method in Vault:

   vault auth enable kubernetes

8. Configure the Kubernetes authentication method in Vault:

   vault write auth/kubernetes/config \
     token_reviewer_jwt="$(cat /var/run/secrets/kubernetes.io/serviceaccount/token)" \
     kubernetes_host="https://${KUBERNETES_SERVICE_HOST}:${KUBERNETES_SERVICE_PORT_HTTPS}" \
     kubernetes_ca_cert=@/var/run/secrets/kubernetes.io/serviceaccount/ca.crt

9. Create a policy for your application:

   cat <<EOF > myapp-policy.hcl
   path "secret/myapp/access" {
     capabilities = ["create", "update", "read"]
   }
   EOF

10. Create the policy in Vault:

    vault policy write myapp-policy myapp-policy.hcl
    
    ## second option
    vault policy write myapp-policy - << EOF
    path "secret/myapp/access" {
        capabilities = ["create", "update", "read"]
    }
    EOF

11. Create a Kubernetes role for Vault:

    vault write auth/kubernetes/role/vault-aws \
      bound_service_account_names=vault-auth \
      bound_service_account_namespaces=default \
      policies=myapp-policy \
      ttl=24h

12. Create a Kubernetes secret in Vault:

    vault kv put secret/myapp/access username="myuser" password="mypassword"

13. Verify that the Kubernetes secret was created in Vault:

    vault kv get secret/myapp/access

Note that you may need to modify some of the values (e.g., the bound_service_account_names in Step 12) to fit your specific use case. Also, make sure to replace myapp with the name of your own application.

15. Inject the secret into nginx pod

You can use annotations in your pod's YAML file to specify which secrets to inject and how to inject them. Here's an example YAML file:

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    app: nginx
  name: nginx
  namespace: default
spec:
  replicas: 1
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      annotations:
        vault.hashicorp.com/agent-inject: "true"
        vault.hashicorp.com/agent-inject-secret-username: creds/vault/access
        vault.hashicorp.com/role: vault-aws
      creationTimestamp: null
      labels:
        app: nginx
    spec:
      containers:
      - image: nginx
        imagePullPolicy: Always
        name: nginx
      securityContext: {}
      serviceAccount: vault-auth 
      serviceAccountName: vault-auth