Systemd Secret Store Plugin

This plugin allows utilizing credentials and secrets provided to the Telegraf service by systemd. Systemd ensures that only the intended service can access the credentials for the lifetime of this service. The credentials appear as plaintext files to the consuming service but are stored encrypted on the host system. This encryption can also use TPM2 protection if available (see this article for details).

This plugin does not support setting the credentials. See the credentials management section below for how to setup systemd credentials and how to add credentials

Introduced in: Telegraf v1.29.0 Tags: system OS support: all

Usage

Secrets defined by a store are referenced with @{<store-id>:<secret_key>} the Telegraf configuration. Only certain Telegraf plugins and options of support secret stores. To see which plugins and options support secrets, see their respective documentation (e.g. plugins/outputs/influxdb/README.md). If the plugin’s README has the Secret store support section, it will detail which options support secret store usage.

Configuration

# Reading systemd credentials
[[secretstores.systemd]]
  ## Unique identifier for the secret store.
  ## This id can later be used in plugins to reference the secrets
  ## in this secret store via @{<id>:<secret_key>} (mandatory)
  id = "systemd"

  ## Path to systemd credentials directory
  ## This should not be required as systemd indicates this directory
  ## via the CREDENTIALS_DIRECTORY environment variable.
  # path = "${CREDENTIALS_DIRECTORY}"

  ## Prefix to remove from systemd credential-filenames to derive secret names
  # prefix = "telegraf."

Each Secret provided by systemd will be available as file under ${CREDENTIALS_DIRECTORY}/<secret-name> for the service. You will not be able to see them as a regular, non-telegraf user. Credential visibility from other systemd services is mediated by the User= and PrivateMounts= service-unit directives for those services. See the systemd.exec man-page for details.

Credential management

Most steps here are condensed from the systemd-creds man-page. Please also check that man-page as the options or verbs used here might be outdated for the systemd version you are using.

Setting up systemd-credentials might vary on your distribution or version so please also check the documentation there. You might also need to install supporting packages such as tpm2-tools.

Setup

Systemd requires a first-time setup of the credential system. If you are planning to use the TPM2 chip of your system for protecting the credentials, you should first make sure that it is available using

sudo systemd-creds has-tpm2

The output should look similar to

partial
-firmware
+driver
+system
+subsystem

If TPM2 is available on your system, credentials can also be tied to the device by utilizing TPM2 sealing. See the systemd-creds man-page for details.

Now setup the credentials by creating the root key.

sudo systemd-creds setup

A warning may appears if you are storing the generated key on an unencrypted disk which is not recommended. With this, we are all set to create credentials.

Creating credentials

After setting up the encryption key we can create a new credential using

echo -n "john-doe-jr" | sudo systemd-creds encrypt - /etc/credstore.encrypted/telegraf.http_user

You should now have a file named telegraf.http_user containing the encrypted username. The secret store later provides the secret using this filename as the secret’s key.

We can now add more secrets. To avoid potentially leaking the plain-text credentials through command-history or showing it on the screen we use

systemd-ask-password -n | sudo systemd-creds encrypt - /etc/credstore.encrypted/telegraf.http_password

to interactively enter the password.

Using credentials as secrets

To use the credentials as secrets you need to first instantiate a systemd secret store by adding

[[secretstores.systemd]]
  id = "systemd"

to your Telegraf configuration. Assuming the two example credentials http_user and http_password you can now use those as secrets via

[[inputs.http]]
  urls = ["http://localhost/metrics"]
  username = "@{systemd:http_user}"
  password = "@{systemd:http_password}"

in your plugins.

Chaining for unattended start

When using many secrets or when secrets need to be shared among hosts, listing all of them in the service file might be cumbersome. Additionally, it is hard to manually test Telegraf configurations with the systemd secret store as those secrets are only available when started as a service.

Here, secret store chaining comes into play, denoting a setup where one secret store, in our case secretstores.systemd, is used to unlock another secret store (secretstores.jose in this example).

[[secretstores.systemd]]
  id = "systemd"

[[secretstores.jose]]
  id = "mysecrets"
  path = "/etc/telegraf/secrets"
  password = "@{systemd:initial}"

Here we assume that an initial credential was injected through the service file. This initial secret is then used to unlock the jose secret store which might provide many different secrets backed by encrypted files.

Input and output plugins can the use the jose secrets (via @{mysecrets:...}) to fill sensitive data such as usernames, passwords or tokens.

Troubleshooting

Please always make sure your systemd version matches Telegraf’s requirements.

When not being able to start the service please check the logs. A common issue is using the --name option which does not work with systemd’s ImportCredential setting. Check for a mismatch between the name stored in the credential (given during systemd-creds encrypt) and the one used in the LoadCredentialEncrypted statement.

In case you are having trouble referencing credentials in Telegraf, you should check what is available via

CREDENTIALS_DIRECTORY=/etc/credstore.encrypted sudo systemd-creds list

for the example above you should see

NAME                   SECURE   SIZE PATH
-------------------------------------------------------------------
telegraf.http_password insecure 146B /etc/credstore.encrypted/telegraf.http_password
telegraf.http_user     insecure 142B /etc/credstore.encrypted/telegraf.http_user

Remember to remove the prefix configured in your secret store from the NAME column to get the secrets’ key.

To get the actual value of a credential use

sudo systemd-creds decrypt /etc/credstore.encrypted/telegraf.http_password -

Please use the above command(s) with care as they do reveal the secret value of the credential!

Additional Information

This plugin only supports reading the secrets, it cannot create or modify them.