HashiCorp Vault, is a powerful secrets management and data protection tool designed to help organizations securely store, access, and control sensitive information across systems, applications, and environments. From API keys and database credentials to encryption keys and dynamic secrets, Vault acts as a centralized fortress for your most critical assets.

But sometimes great capabilities come with a high cost.

As Vault Enterprise becomes more deeply integrated into your infrastructure, its operational footprint can grow—leading to unexpected billing spikes.

Understanding how to optimize Vault usage without compromising on security is key to keeping both your secrets safe and your budget in check.

In the following article I will be teaching you ways to vault like a pro , without hurting your pockets ! By leveraging the power of Sentinel Endpoint Governing Policies , you too can control the number of your entities and avoid a hefty bill at the end of the year !

Vault pricing is based on the number of clients: a mechanism that requires companies to stay vigilant

By definition a client is any entity that establishes a connection and authenticates to carry out an operation. This could be a person accessing the vault cluster to configure the policies or an application retrieving a database password.

In cloud-native environments, the number of clients can scale rapidly, often without obvious signs - creating a cost explosion. For instance, scaling up your Kubernetes pods during a traffic peak can triple the number of clients. Retrieving secrets from vault in your CI/CD pipelines, could mean that every job ran is a client also.

Vault’s client-based pricing model is theoretically simple, but risky if you’re not familiar with it—especially in architectures relying on automation, elasticity, or ephemeral services. Client numbers can multiply exponentially, putting you at risk of budget overruns or vendor lock-in surprises.

Vault’s client-based pricing model is theoretically simple, but risky if you’re not familiar with it—especially in architectures relying on automation, elasticity, or ephemeral services. Client numbers can multiply exponentially, putting you at risk of budget overruns or vendor lock-in surprises.

The solution: Sentinel to control Vault entity growth

To address this, Sentinel—HashiCorp’s policy-as-code framework—can enforce guardrails that limit client growth, prevent misuse, and ensure compliance with internal cost controls.
Sentinel Endpoint Governing Policies (EGP) is a policy enforcement framework in Vault Enterprise that allows organizations to define and apply custom rules (written in Sentinel) before certain operations are allowed. This enables custom business logic, dynamic context-aware restrictions, and the integration of compliance and security guardrails directly into Vault workflows.
In the context of client limitation, Sentinel EGP allows you to define a maximum number of active entities per namespace.
This cap can be enforced by:

  • limiting the number of AppRole or OIDC roles a client can create,
  • or denying token creation if the number of entities exceeds the threshold.

Let’s take the use case of sentinel policy the limits the number of approle roles created in a namespace as an example. 

import "http"
check_number_of_existing_entities= func () {
#Request to the vault API to get the number of entities in the namespace
}

#You can use Reggex to the better represent the request.path 
main = rule when request.path matches "auth/approle/role/*" and 
                                 request.operation in ["create"] {
 if check_number_of_existing_entities > limit_of_entities_per_namespace {
 #This is very basic implemntation the policy and doesn't treat all the spacial cases 
 return false
 }
 return true
}

The next case is for ldap auth method where we deny the creation of the token , if the user doesn’t already have an entity. 


import "http"
check_number_of_existing_entities= func () {
#Request to the vault API to get the number of entities in the namespace
}
check_if_user_exists_already= func () {
#Request to the vault API to check if an entity with an aliase of the ldap username exists or not. 
}
#You can use Reggex to the better represent the request.path 
main = rule when request.path matches "auth/ldap/login" and 
                                 request.operation in ["update"] {
 if check_number_of_existing_entities > limit_of_entities_per_namespace & !check_if_user_exists_already{
 #This is very basic implementation the policy and doesn't treat all the spacial case 
 return false
 }
 return true
}

Vault governance: From reactive to proactive

By integrating Sentinel into your Vault setup, you shift from a reactive approach—where budget overruns are discovered too late—to a proactive governance model where such spikes are prevented ahead of time.
Often, teams don’t realize how many clients are connecting to Vault until the bill arrives. With Sentinel, you can define policies to prevent these spikes from happening. This approach embeds cost awareness into daily operations, treating financial constraints as seriously as security rules.

Sentinel: Your automated safeguard

Sentinel policies act as automatic safeguards, evaluating each request in real time to determine whether it respects your organization’s usage boundaries.

At Lenstra, we’ve helped clients:

  • control their Vault usage growth without constant human oversight,
  • ensure license compliance by capping the number of clients,
  • gain clarity on what qualifies as an entity, review namespace access, revoke unused rights, and clean up obsolete role configurations.

A secure cloud doesn’t mean uncontrolled spending

Security doesn’t have to come at the cost of your budget. With the right guardrails, you can run a robust, cloud-native architecture without letting costs spiral out of control.
Adopting Sentinel EGP has enabled our clients to maintain strong Vault security controls while staying cost-efficient.

If you’re using Vault—especially in dynamic environments—now is the time to review your access patterns, token usage, and entity sprawl.

Ask yourself:

  • Are we monitoring how many clients actually connect to Vault?
  • Do we have policies in place to prevent misuse or overuse?
  • Are our cost controls as automated as our infrastructure?

Don’t let billing surprises catch you off guard.
Need guidance? Contact us!