Vault Agent Templates

Vault Agent's Template functionality allows Vault secrets to be rendered to files using Consul Template markup.

For globally applicable templating engine configuration, refer to the parameters within the template_config stanza.

Functionality

The template stanza configures the Vault agent for rendering secrets to files using Consul Template markup language. Multiple template stanzas can be defined to render multiple files.

When the agent is started with templating enabled, it will attempt to acquire a Vault token using the configured auto-auth Method. On failure, it will back off for a short while (including some randomness to help prevent thundering herd scenarios) and retry. On success, secrets defined in the templates will be retrieved from Vault and rendered locally.

Configuration

The top level template block has multiple configurations entries:

source (string: "") - Path on disk to use as the input template. This option is required if not using the contents option.
destination (string: required) - Path on disk where the rendered secrets should be created. If the parent directories If the parent directories do not exist, Vault Agent will attempt to create them, unless create_dest_dirs is false.
create_dest_dirs (bool: true) - This option tells Vault Agent to create the parent directories of the destination path if they do not exist.
contents (string: "") - This option allows embedding the contents of a template in the configuration file rather then supplying the source path to the template file. This is useful for short templates. This option is mutually exclusive with the source option.
command (string: "") - This is the optional command to run when the template is rendered. The command will only run if the resulting template changes. The command must return within 30s (configurable), and it must have a successful exit code. Vault Agent is not a replacement for a process monitor or init system.
command_timeout (duration: 30s) - This is the maximum amount of time to wait for the optional command to return.
error_on_missing_key (bool: false) - Exit with an error when accessing a struct or map field/key that does notexist. The default behavior will print <no value> when accessing a field that does not exist. It is highly recommended you set this to "true".
perms (string: "") - This is the permission to render the file. If this option is left unspecified, Vault Agent will attempt to match the permissions of the file that already exists at the destination path. If no file exists at that path, the permissions are 0644.
backup (bool: true) - This option backs up the previously rendered template at the destination path before writing a new one. It keeps exactly one backup. This option is useful for preventing accidental changes to the data without having a rollback strategy.
left_delimiter (string: "{{") - Delimiter to use in the template. The default is "{{" but for some templates, it may be easier to use a different delimiter that does not conflict with the output file itself.
right_delimiter (string: "}}") - Delimiter to use in the template. The default is "}}" but for some templates, it may be easier to use a different delimiter that does not conflict with the output file itself.
sandbox_path (string: "") - If a sandbox path is provided, any path provided to the file function is checked that it falls within the sandbox path. Relative paths that try to traverse outside the sandbox path will exit with an error.
wait (object: required) - This is the minimum(:maximum) to wait before rendering a new template to disk and triggering a command, separated by a colon (:).

Example Template

Template with Vault Agent requires the use of the secret function from Consul Template. The following is an example of a template that retrieves a generic secret from Vault's KV store:

{{ with secret "secret/my-secret" }}
{{ .Data.data.foo }}
{{ end }}

Example Configuration

The following demonstrates configuring Vault Agent to template secrets using the AppRole Auth method:

pid_file = "./pidfile"

vault {
  address = "https://127.0.0.1:8200"
}

auto_auth {
  method {
    type = "approle"

    config = {
      role_id_file_path = "/etc/vault/roleid"
      secret_id_file_path = "/etc/vault/secretid"
    }
  }

  sink {
    type = "file"

    config = {
      path = "/tmp/file-foo"
    }
  }
}

template {
  source      = "/tmp/agent/template.ctmpl"
  destination = "/tmp/agent/render.txt"
}

If you only want to use the Vault agent to render one or more templates and do not need to sink the acquired credentials, you can omit the sink stanza from the auto_auth stanza in the agent configuration.

Renewals and Updating Secrets

The Vault Agent templating automatically renews and fetches secrets/tokens. Unlike Vault Agent caching, the behavior of how Vault Agent templating does this depends on the type of secret or token. The following is a high level overview of different behaviors.

Renewable Secrets

If a secret or token is renewable, Vault Agent will renew the secret after 2/3 of the secret's lease duration has elapsed.

Non-Renewable Secrets

If a secret or token isn't renewable or leased, Vault Agent will fetch the secret every 5 minutes. This is not configurable. Non-renewable secrets include (but not limited to) KV Version 2.

Non-Renewable Leased Secrets

If a secret or token is non-renewable but leased, Vault Agent will fetch the secret when 85% of the secrets time-to-live (TTL) is reached. Leased, non-renewable secrets include (but not limited to) dynamic secrets such as database credentials and KV Version 1.

Static Roles

If a secret has a rotation_period, such as a database static role, Vault Agent template will fetch the new secret as it changes in Vault. It does this by inspecting the secret's time-to-live (TTL).

Certificates

If a secret is a certificate, Vault Agent template will fetch the new certificate using the certificates validTo field.

This does not apply to certificates generated with generate_lease: true. If set Vault Agent template will apply the non-renewable, leased secret rules.