Implementing Hashicorp Vault Dynamic Secrets

Implementing HashiCorp Vault Dynamic Secrets

When to Use

• Applications use static database credentials stored in configuration files or environment variables
• AWS IAM access keys are long-lived and shared across services
• Need to eliminate credential sprawl by generating short-lived, per-request secrets
• Compliance requirements mandate credential rotation (PCI-DSS Requirement 8, NIST 800-53 IA-5)
• Implementing zero-trust secret management where credentials are never stored at rest
• Migrating from manual credential management to automated secrets lifecycle

Do not use for storing static secrets that cannot be dynamically generated (use Vault's KV secrets engine instead); dynamic secrets are for credentials that can be programmatically created and revoked on target systems.

Common Misconfigurations & Verification

Dynamic secrets only reduce risk if leases are short and actually revoked — these defeat the point:

• TTL/max_ttl too long: a role with default_ttl=720h is functionally a static secret. Audit with vault read database/roles/app-readonly and confirm default_ttl is minutes-to-hours, not days. Check live lease ages: vault list sys/leases/lookup/database/creds/app-readonly.
• Leases never revoked on shutdown: apps that exit without calling revoke leave credentials valid until max_ttl, accumulating orphaned DB users. Count them on the target (SELECT rolname FROM pg_roles WHERE rolname LIKE 'v-%') and compare to active leases — a large delta means revocation is broken. Confirm the client calls sys.revoke_lease on teardown.
• Missing/incorrect revocation_statements: the lease expires in Vault but the DB role/user is never dropped. Verify every role has DROP ROLE/USER in its revocation block and test by reading a cred, force-revoking (vault lease revoke -prefix database/creds/...), then confirming the DB user is gone.
• Root credential not rotated: the bootstrap admin password is still known to humans. Confirm vault write -force database/rotate-root/... was run; the original password must no longer authenticate.
• AWS iam_user where assumed_role/STS would do: long-lived-ish keys with slow IAM propagation. Prefer credential_type=assumed_role and verify default_sts_ttl/max_sts_ttl are short.
• No audit device / no alerting on lease spikes: confirm vault audit list shows an enabled device and that a sudden surge in database/creds reads triggers a SIEM alert (credential exfiltration signal).

Prerequisites

• HashiCorp Vault 1.15+ (Community or Enterprise edition)
• Vault server initialized and unsealed with auto-unseal configured (AWS KMS, Azure Key Vault, or Transit)
• Target database systems with admin credentials for Vault to create/revoke dynamic accounts
• AWS IAM account with permissions to create/delete IAM users and access keys
• Network connectivity from Vault to all target systems
• Vault policies and authentication methods configured for consuming applications

Workflow

Step 1: Deploy and Configure Vault Server

Initialize Vault with production-grade configuration:

# vault-config.hcl - Production Vault server configuration
storage "raft" {
  path    = "/opt/vault/data"
  node_id = "vault-1"

  retry_join {
    leader_api_addr = "https://vault-2.corp.local:8200"
  }
  retry_join {
    leader_api_addr = "https://vault-3.corp.local:8200"
  }
}

listener "tcp" {
  address       = "0.0.0.0:8200"
  tls_cert_file = "/opt/vault/tls/vault-cert.pem"
  tls_key_file  = "/opt/vault/tls/vault-key.pem"
}

seal "awskms" {
  region     = "us-east-1"
  kms_key_id = "alias/vault-unseal-key"
}

api_addr      = "https://vault-1.corp.local:8200"
cluster_addr  = "https://vault-1.corp.local:8201"

telemetry {
  prometheus_retention_time = "24h"
  disable_hostname          = true
}

ui = true

# Initialize Vault cluster
vault operator init -key-shares=5 -key-threshold=3

# Enable audit logging
vault audit enable file file_path=/var/log/vault/audit.log

# Enable AppRole authentication for applications
vault auth enable approle

# Create policy for database secret consumers
vault policy write db-consumer - <<EOF
# Allow reading dynamic database credentials
path "database/creds/app-readonly" {
  capabilities = ["read"]
}
path "database/creds/app-readwrite" {
  capabilities = ["read"]
}

# Allow renewing and revoking own leases
path "sys/leases/renew" {
  capabilities = ["update"]
}
path "sys/leases/revoke" {
  capabilities = ["update"]
}

# Allow reading own token info
path "auth/token/lookup-self" {
  capabilities = ["read"]
}
EOF

# Create AppRole for application
vault write auth/approle/role/webapp \
    token_policies="db-consumer" \
    token_ttl=1h \
    token_max_ttl=4h \
    secret_id_ttl=720h \
    secret_id_num_uses=0

Step 2: Configure Database Secrets Engine

Set up dynamic credential generation for PostgreSQL and MySQL:

# Enable the database secrets engine
vault secrets enable database

# Configure PostgreSQL connection
vault write database/config/production-postgres \
    plugin_name=postgresql-database-plugin \
    allowed_roles="app-readonly,app-readwrite,app-admin" \
    connection_url="postgresql://{{username}}:{{password}}@db-primary.corp.local:5432/appdb?sslmode=verify-full" \
    username="vault_admin" \
    password="$VAULT_DB_PASSWORD" \
    password_authentication="scram-sha-256"

# Rotate the root credentials so Vault manages them exclusively
vault write -force database/rotate-root/production-postgres

# Create read-only role (TTL: 1 hour, max 24 hours)
vault write database/roles/app-readonly \
    db_name=production-postgres \
    creation_statements="CREATE ROLE \"{{name}}\" WITH LOGIN PASSWORD '{{password}}' VALID UNTIL '{{expiration}}'; \
        GRANT SELECT ON ALL TABLES IN SCHEMA public TO \"{{name}}\"; \
        ALTER DEFAULT PRIVILEGES IN SCHEMA public GRANT SELECT ON TABLES TO \"{{name}}\";" \
    revocation_statements="REVOKE ALL PRIVILEGES ON ALL TABLES IN SCHEMA public FROM \"{{name}}\"; \
        DROP ROLE IF EXISTS \"{{name}}\";" \
    default_ttl="1h" \
    max_ttl="24h"

# Create read-write role (TTL: 30 minutes, max 8 hours)
vault write database/roles/app-readwrite \
    db_name=production-postgres \
    creation_statements="CREATE ROLE \"{{name}}\" WITH LOGIN PASSWORD '{{password}}' VALID UNTIL '{{expiration}}'; \
        GRANT SELECT, INSERT, UPDATE, DELETE ON ALL TABLES IN SCHEMA public TO \"{{name}}\"; \
        ALTER DEFAULT PRIVILEGES IN SCHEMA public GRANT SELECT, INSERT, UPDATE, DELETE ON TABLES TO \"{{name}}\";" \
    revocation_statements="REVOKE ALL PRIVILEGES ON ALL TABLES IN SCHEMA public FROM \"{{name}}\"; \
        DROP ROLE IF EXISTS \"{{name}}\";" \
    default_ttl="30m" \
    max_ttl="8h"

# Configure MySQL connection
vault write database/config/production-mysql \
    plugin_name=mysql-database-plugin \
    allowed_roles="mysql-readonly,mysql-readwrite" \
    connection_url="{{username}}:{{password}}@tcp(mysql-primary.corp.local:3306)/" \
    username="vault_admin" \
    password="$VAULT_MYSQL_PASSWORD"

vault write database/roles/mysql-readonly \
    db_name=production-mysql \
    creation_statements="CREATE USER '{{name}}'@'%' IDENTIFIED BY '{{password}}'; \
        GRANT SELECT ON appdb.* TO '{{name}}'@'%';" \
    revocation_statements="DROP USER IF EXISTS '{{name}}'@'%';" \
    default_ttl="1h" \
    max_ttl="24h"

# Test dynamic credential generation
echo "Testing PostgreSQL dynamic credentials:"
vault read database/creds/app-readonly
# Returns: username=v-approle-app-read-xxxxx, password=<random>, lease_id=database/creds/app-readonly/xxxxx

Step 3: Configure AWS Secrets Engine

Generate ephemeral AWS IAM credentials:

# Enable the AWS secrets engine
vault secrets enable aws

# Configure the AWS secrets engine with root credentials
vault write aws/config/root \
    access_key="$AWS_ACCESS_KEY_ID" \
    secret_key="$AWS_SECRET_ACCESS_KEY" \
    region="us-east-1"

# Configure lease settings
vault write aws/config/lease \
    lease="30m" \
    lease_max="1h"

# Create IAM User role for S3 read-only access
vault write aws/roles/s3-readonly \
    credential_type=iam_user \
    policy_document=-<<EOF
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "s3:GetObject",
        "s3:ListBucket",
        "s3:GetBucketLocation"
      ],
      "Resource": [
        "arn:aws:s3:::app-data-bucket",
        "arn:aws:s3:::app-data-bucket/*"
      ]
    }
  ]
}
EOF

# Create Assumed Role for EC2 management (preferred over IAM users)
vault write aws/roles/ec2-admin \
    credential_type=assumed_role \
    role_arns="arn:aws:iam::123456789012:role/VaultEC2AdminRole" \
    default_sts_ttl="30m" \
    max_sts_ttl="1h"

# Create Federation Token role for cross-account access
vault write aws/roles/cross-account-readonly \
    credential_type=federation_token \
    policy_document=-<<EOF
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "sts:AssumeRole"
      ],
      "Resource": "arn:aws:iam::987654321098:role/CrossAccountReadOnly"
    }
  ]
}
EOF

# Test AWS dynamic credentials
echo "Testing AWS STS credentials:"
vault read aws/creds/ec2-admin
# Returns: access_key, secret_key, security_token with 30-minute TTL

Step 4: Configure PKI Secrets Engine for Dynamic Certificates

Generate short-lived TLS certificates on demand:

# Enable PKI secrets engine for root CA
vault secrets enable -path=pki pki
vault secrets tune -max-lease-ttl=87600h pki

# Generate root CA certificate
vault write pki/root/generate/internal \
    common_name="Corp Internal Root CA" \
    ttl=87600h \
    key_type=ec \
    key_bits=384

# Enable PKI for intermediate CA
vault secrets enable -path=pki_int pki
vault secrets tune -max-lease-ttl=43800h pki_int

# Generate intermediate CA CSR
vault write pki_int/intermediate/generate/internal \
    common_name="Corp Intermediate CA" \
    key_type=ec \
    key_bits=256

# Sign intermediate CA with root CA
vault write pki/root/sign-intermediate \
    csr=@intermediate.csr \
    format=pem_bundle \
    ttl=43800h

# Configure issuing URLs
vault write pki_int/config/urls \
    issuing_certificates="https://vault.corp.local:8200/v1/pki_int/ca" \
    crl_distribution_points="https://vault.corp.local:8200/v1/pki_int/crl"

# Create role for web server certificates (TTL: 30 days)
vault write pki_int/roles/web-server \
    allowed_domains="corp.local,internal.corp.com" \
    allow_subdomains=true \
    max_ttl=720h \
    key_type=ec \
    key_bits=256 \
    require_cn=true \
    enforce_hostnames=true

# Create role for service mesh certificates (TTL: 24 hours)
vault write pki_int/roles/service-mesh \
    allowed_domains="service.consul" \
    allow_subdomains=true \
    max_ttl=24h \
    key_type=ec \
    key_bits=256 \
    allow_ip_sans=true \
    server_flag=true \
    client_flag=true

# Issue a certificate
vault write pki_int/issue/web-server \
    common_name="api.corp.local" \
    alt_names="api.internal.corp.com" \
    ttl=720h

Step 5: Integrate Applications with Vault

Configure applications to consume dynamic secrets:

"""
Application integration with HashiCorp Vault for dynamic database credentials.
Uses the hvac Python client with automatic lease renewal.
"""
import hvac
import threading
import time
import logging

class VaultDynamicCredentialManager:
    def __init__(self, vault_addr, role_id, secret_id):
        self.client = hvac.Client(url=vault_addr)
        self.role_id = role_id
        self.secret_id = secret_id
        self.logger = logging.getLogger("vault_credentials")
        self._current_creds = None
        self._lease_id = None
        self._renewal_thread = None
        self._stop_event = threading.Event()

    def authenticate(self):
        """Authenticate to Vault using AppRole."""
        response = self.client.auth.approle.login(
            role_id=self.role_id,
            secret_id=self.secret_id
        )
        self.client.token = response["auth"]["client_token"]
        self.logger.info("Authenticated to Vault via AppRole")

    def get_database_credentials(self, role="app-readonly"):
        """Request dynamic database credentials from Vault."""
        self.authenticate()

        response = self.client.secrets.database.generate_credentials(
            name=role
        )

        self._current_creds = {
            "username": response["data"]["username"],
            "password": response["data"]["password"],
        }
        self._lease_id = response["lease_id"]
        lease_duration = response["lease_duration"]

        self.logger.info(
            f"Obtained dynamic credentials: user={self._current_creds['username']}, "
            f"lease={self._lease_id}, ttl={lease_duration}s"
        )

        # Start background lease renewal
        self._start_renewal(lease_duration)

        return self._current_creds

    def _start_renewal(self, lease_duration):
        """Start background thread to renew lease before expiration."""
        if self._renewal_thread and self._renewal_thread.is_alive():
            self._stop_event.set()
            self._renewal_thread.join()

        self._stop_event.clear()
        renewal_interval = lease_duration * 0.7  # Renew at 70% of TTL

        def renew_loop():
            while not self._stop_event.wait(renewal_interval):
                try:
                    self.client.sys.renew_lease(
                        lease_id=self._lease_id,
                        increment=lease_duration
                    )
                    self.logger.info(f"Renewed lease: {self._lease_id}")
                except hvac.exceptions.InvalidRequest:
                    self.logger.warning("Lease expired, obtaining new credentials")
                    self.get_database_credentials()
                    break
                except Exception as e:
                    self.logger.error(f"Lease renewal failed: {e}")

        self._renewal_thread = threading.Thread(target=renew_loop, daemon=True)
        self._renewal_thread.start()

    def revoke_credentials(self):
        """Explicitly revoke current dynamic credentials."""
        if self._lease_id:
            self._stop_event.set()
            self.client.sys.revoke_lease(self._lease_id)
            self.logger.info(f"Revoked lease: {self._lease_id}")
            self._current_creds = None
            self._lease_id = None

    def get_aws_credentials(self, role="s3-readonly"):
        """Request dynamic AWS credentials from Vault."""
        self.authenticate()

        response = self.client.secrets.aws.generate_credentials(
            name=role
        )

        return {
            "access_key": response["data"]["access_key"],
            "secret_key": response["data"]["secret_key"],
            "security_token": response["data"].get("security_token"),
            "lease_id": response["lease_id"],
            "ttl": response["lease_duration"]
        }

# Usage example
vault_mgr = VaultDynamicCredentialManager(
    vault_addr="https://vault.corp.local:8200",
    role_id="<approle-role-id>",
    secret_id="<approle-secret-id>"
)

db_creds = vault_mgr.get_database_credentials("app-readonly")
# Use db_creds["username"] and db_creds["password"] for database connection

Step 6: Monitor Vault Operations and Lease Management

Track dynamic secret usage and lease lifecycle:

# Monitor active leases
vault list sys/leases/lookup/database/creds/app-readonly
vault list sys/leases/lookup/aws/creds/s3-readonly

# Check lease details
vault write sys/leases/lookup lease_id="database/creds/app-readonly/abcd1234"

# Revoke all leases for a specific path (emergency credential rotation)
vault lease revoke -prefix database/creds/app-readonly

# Vault metrics for monitoring (Prometheus format)
# Key metrics to monitor:
# vault.expire.num_leases - Total active leases
# vault.expire.revoke - Lease revocations per second
# vault.secret.kv.count - Total stored secrets
# vault.runtime.alloc_bytes - Memory allocation

# Configure Vault audit log analysis
cat > vault_audit_monitor.sh << 'SCRIPT'
#!/bin/bash
# Monitor Vault audit logs for suspicious activity

AUDIT_LOG="/var/log/vault/audit.log"

# Count credential requests per hour
echo "=== Dynamic Credential Requests (Last Hour) ==="
jq -r 'select(.type == "response" and .request.path | startswith("database/creds/")) |
    "\(.time) \(.request.path) \(.auth.display_name)"' \
    "$AUDIT_LOG" | tail -100

# Detect unusual credential request patterns
echo ""
echo "=== High-Volume Credential Consumers ==="
jq -r 'select(.type == "request" and .request.path | startswith("database/creds/")) |
    .auth.display_name' \
    "$AUDIT_LOG" | sort | uniq -c | sort -rn | head -10

# Check for failed authentication attempts
echo ""
echo "=== Failed Auth Attempts ==="
jq -r 'select(.type == "response" and .error != null and
    .request.path | startswith("auth/")) |
    "\(.time) \(.request.path) \(.error)"' \
    "$AUDIT_LOG" | tail -20
SCRIPT
chmod +x vault_audit_monitor.sh

Key Concepts

Tools & Systems

• HashiCorp Vault: Secrets management platform providing dynamic secrets, encryption as a service, and identity-based access control
• Vault Agent: Sidecar process that handles Vault authentication, token renewal, and secret caching for applications
• Vault Secrets Operator: Kubernetes operator that syncs Vault secrets into Kubernetes Secrets for pod consumption
• hvac: Python client library for HashiCorp Vault API operations

Common Scenarios

Scenario: Eliminating Static Database Credentials in Microservices

Context: 50 microservices share 3 static PostgreSQL credentials stored in environment variables across Kubernetes deployments. A credential leak requires rotating all 50 services simultaneously.

Approach:

1. Deploy Vault with Raft storage in a 3-node HA cluster within Kubernetes
2. Configure database secrets engine with PostgreSQL connection using admin credentials
3. Create per-service Vault roles with least-privilege SQL grants
4. Deploy Vault Secrets Operator to inject dynamic credentials into pod environment variables
5. Update application connection logic to handle credential rotation via lease renewal
6. Rotate the Vault root credential to remove human knowledge of the admin password
7. Monitor lease lifecycle and set alerts for renewal failures

Pitfalls:

• Not handling credential rotation in application connection pools (connections using expired credentials fail)
• Setting TTLs too short causes excessive credential generation load on the database
• Not configuring proper revocation statements leaves orphaned database users after lease expiration
• Running Vault without HA causes single point of failure for all application authentication

Output Format

HASHICORP VAULT DYNAMIC SECRETS REPORT
=========================================
Vault Version:     1.16.2 Enterprise
Cluster Status:    HA Active (3 nodes)
Seal Type:         AWS KMS (auto-unseal)

SECRETS ENGINES
database/:         PostgreSQL, MySQL (2 connections)
aws/:              IAM User, Assumed Role, Federation Token
pki_int/:          Internal CA (EC P-256)

DYNAMIC CREDENTIAL METRICS (Last 24 Hours)
Total Credentials Generated:    4,287
  Database (PostgreSQL):        2,891
  Database (MySQL):             543
  AWS STS:                      612
  PKI Certificates:             241

ACTIVE LEASES
Total Active:                   387
  database/creds/app-readonly:  198
  database/creds/app-readwrite: 89
  aws/creds/s3-readonly:        67
  pki_int/issue/web-server:     33

LEASE LIFECYCLE
Average TTL:                    45 minutes
Renewals (24h):                 12,847
Revocations (24h):              3,901
Expired (not renewed):          12

SECURITY
Failed Auth Attempts (24h):     3
Root Credential Rotated:        YES (all databases)
Audit Logging:                  ENABLED (file + syslog)
Policy Violations (24h):        7 (permission denied)