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Vault PKI Formula

A SaltStack formula to issue and automatically update and distribute certificates from a private certificate authority backed by Hashicorp Vault.

Server-side installation and operation is covered in the documentation for the Vault PKI Runner. This formula requires the associated Vault PKI Runner to be installed on the Salt master to operate.

Overview of Operation

Below is an overview of the operation of the client-side (minion-side) functionality of Vault PKI.

Events from the minion perspective, during first application, in order:

  1. cert state installs client at /usr/local/bin/vault_pki
  2. cert state runs vault_pki checkgen which creates the /etc/vault_pki directory structure, generates a CSR and fires a Salt event with the CSR and other data to request a signed certificate.
  3. Server side magic modifies the CSR and gets it signed, see Vault PKI Runner docs for details.
  4. More server side magic writes the signed certificate to the minion and runs the react_activate_cert state on minion. The state in turn runs vault_pki activate with the new certificate version.
  5. Activation ensures the key, signed certificate, and full certificate chain of the new version are all in place. Symbolic links in the live directory are all updated to the new version or none are.
  6. If activation of the new certificate version was successful the /etc/vault_pki/post-activate.d directory is searched for scripts with the executable bit set. Each script is run in turn logging output.

Usage

Apply the cert state to minions you wish to receive certificates. They will receive certificates according to the defaults and overrides configured on the Salt master (see Vault PKI Runner docs for details).

TLDR;

  • vault_pki checkgen is safe to run. Once up to date certificates are in place it simply verifies the certificate age and exits. If the certificates are too old, or missing, it requests new ones.
  • Minions receive a certificate for their Salt minion id, which should be the hostname but make sure your Salt minion deployment agrees.
  • Any SANs or IPSANs you wish to apply must be specified in the Vault PKI overrides file on the Salt master (on a hostname or a minion pattern basis).
  • Validity periods are also determined from a default setting on the Salt master, or are overridden in aforementioned overrides file.
  • Post-Activation scripts can be setup to kick any server that needs to know about a new certificate being delivered.
  • Certificates are delivered asynchronously and may take up to 10-15 seconds to arrive (vault_pki checkgen, currently, does not block and wait for them and instead logs the certificate request was sent and exits).

Always configure servers to use the keys and certificates in the /etc/vault_pki/live/$hostname directory.

This ensures when the certificate is updated your server does not need to be reconfigured (maybe just reloaded/restarted/etc). (If you simply must copy the key and certificate out of the managed directory see Note 1).

Post-Activation: To ensure your running servers are informed of a new certificate upon delivery, create a script to notify your service as desired and place it in /etc/vault_pki/post-activate.d/ with the executable bit set.

Important Caveat: Because the cert state incorporates asynchronous behavior it is not currently possible to use it in a requisite properly. (e.g. to make the nginx state require the cert be applied first -- without which can lead to nginx starting up and crashing because certificates haven't been delivered yet) This is only an issue during the first application of highstate, and a fix is being worked on.

Certificate Updates

A cron job is installed on the minion to ensure it checks the freshness of the certificate once per day -- and will request a new one when the validity period is 50% past.

For example is a minion is issued a certificate valid for 30 days, on the 16th day the minion will request a new certificate.

To force an update sooner, after say adding a new override, simply run vault_pki checkgen --force on the minion.

File + Directory Structure

The directory and file structure for the Vault PKI client was adapted from the EFF project Certbot.

File Purpose
privkey.pem Private key in the OpenSSL traditional format.
privkey.pkcs8 Private key in PKCS#8 -- frequently used by Java programs.
cert.pem The minion certificate with no intermediate chained certificates.
fullchain.pem Minion certificate with all chained certificates--when in doubt use this file.
Directory Purpose
/etc/vault_pki Base directory of Vault PKI client.
/etc/vault_pki/live/$hostname Contains symlinks to active key + certificate version.
/etc/vault_pki/archive/$hostname Contains all versions of certificate material.
/etc/vault_pki/archive/$hostname/$version Certificate material for version X.
/etc/vault_pki/keys/$hostname Contains all version of key material.
/etc/vault_pki/keys/$hostname/$version Key material for version X.

Version numbers are zero-padded 4 digit numbers, starting at 1. Example: 0001, 0002, 0003, ...

Notes

  1. If you must copy the key + certificate material out of the Vault PKI client directory -- do it in a post-activate script if possible so that your server still gets the newest version regularly.