Rendering the Vault Agent token in the Template process

Vault
1

I have a use case such that my Prometheus server needs a vault token in order to hit the vault metrics endpoint. That token needs to be in the prometheus.yaml file before prometheus starts up.

I’m wondering, is there a way to run the vault agent, and in the template rendering process, can I write out the vault token to the destination file? Is there template syntax that allows me to do that?

Any help is much appreciated!

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2

I had the same question and issue yesterday. A coworker showed me the following:

{{ with secret "auth/token/lookup-self" -}}
{{ .Data.id }}
{{ end -}}

This secret is also available using the vault cli:

vault read /auth/token/lookup-self
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3

Amazing! Thanks so much that’s very helpful.

4

You can have it write to a sink file, encrypted or plain text via: Vault Agent Auto-Auth File Sink | Vault by HashiCorp

5

Hi,

I’m working on integrating HashiCorp Vault into our application using Vault Agent for authentication. The initial setup works well, where the application reads the Vault token from a file generated by Vault Agent and uses it to authenticate with the Vault server.

However, I’m concerned about handling scenarios where the token’s max TTL is reached, and a new token is generated by Vault Agent.

Currently, our application reads the token once during initialization and uses it for subsequent operations. If the token expires and a new one is generated, the application wouldn’t automatically know about the new token, which could lead to failed operations.

To address this, I am thinking to implement a file watcher that monitors the token file for changes. When a new token is generated, the watcher reloads the token and updates the Vault client. While this seems to work in theory, I want to ensure that we’re following best practices and not missing any important considerations.

Here are the specific questions I have:

  1. Is monitoring the token file for changes and reloading the token dynamically the recommended approach for handling token renewal with Vault Agent?
  2. Are there any potential pitfalls or edge cases I should be aware of when implementing this solution?
  3. Are there more efficient or reliable methods to ensure the application always has access to a valid token, especially in high-availability or production environments?

I’d appreciate any feedback or suggestions on improving this implementation.

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