Why use Agent or Proxy?

A valid client token must accompany most requests to Vault. This includes all API requests, as well as via the Vault CLI and other libraries. Therefore, Vault clients must first authenticate with Vault to acquire a token. Vault provides several authentication methods to assist in delivering this initial token.

If the client can securely acquire the token, all subsequent requests (e.g., request database credentials, read key/value secrets) are processed based on the trust established by a successful authentication.

This means that client application must invoke the Vault API to authenticate with Vault and manage the acquired token, in addition to invoking the API to request secrets from Vault. This implies code changes to client applications along with additional testing and maintenance of the application.

The following code example implements Vault API to authenticate with Vault through AppRole auth method, and then uses the returned client token to read secrets at kv-v2/data/creds.

package main

import (
    ...snip...
    vault "github.com/hashicorp/vault/api"
)

// Fetches a key-value secret (kv-v2) after authenticating via AppRole
func getSecretWithAppRole() (string, error) {
    config := vault.DefaultConfig()

    client := vault.NewClient(config)
    wrappingToken := ioutil.ReadFile("path/to/wrapping-token")
    unwrappedToken := client.Logical().Unwrap(strings.TrimSuffix(string(wrappingToken), "\n"))

    secretID := unwrappedToken.Data["secret_id"]
    roleID := os.Getenv("APPROLE_ROLE_ID")

    params := map[string]interface{}{
        "role_id":   roleID,
        "secret_id": secretID,
    }
    resp := client.Logical().Write("auth/approle/login", params)
    client.SetToken(resp.Auth.ClientToken)

    secret, err := client.Logical().Read("kv-v2/data/creds")
    if err != nil {
        return "", fmt.Errorf("unable to read secret: %w", err)
    }

    data := secret.Data["data"].(map[string]interface{})

    ...snip...
}

For some Vault deployments, making (and maintaining) these changes to applications may not be a problem, and may actually be preferred. This may be applied to scenarios where you have a small number of applications, or you want to keep strict, customized control over how each application interacts with Vault. However, in other situations where you have a large number of applications, as in large enterprises, you may not have the resources or expertise to update and maintain the Vault integration code for every application. When third party applications are being deployed by the application, it is prohibited to add the Vault integration code.

Introduce Vault Agent and Vault Proxy to the workflow

Vault Agent and Vault Proxy aim to remove this initial hurdle to adopt Vault by providing a more scalable and simpler way for applications to integrate with Vault. Vault Agent can obtain secrets and provide them to applications, and Vault Proxy can act as a proxy between Vault and the application, optionally simplifying the authentication process and caching requests.

As with most other CLI commands for the Vault binary, neither Vault Agent nor Vault Proxy require a Vault Enterprise license, and are available in all Vault binaries and images. Note however that some features, such as static secret caching, are only available when connected to a Vault Enterprise server.

To learn more, refer to the Vault Agent or Vault Proxy documentation page.