How to renew the Puppet CA certificate

Many thanks to https://blog.flyingcircus.io/2017/09/01/how-to-renew-puppet-ca-and-server-certificates-in-place for these instructions.

How to renew Puppet CA and server certificates in place

If you see a message like this when running the puppet agent it is time to renew your certs.

Warning: Certificate 'Puppet CA: puppetmaster.example.com' will expire on 2019-10-14T12:31:13GMT

The CA certificate must be renewed *before* it expires or else you will need to clean and resign *all* of your client node certificates along with the CA cert.

To renew the existing CA cert follow these steps. *BACK UP* your CA data before doing this.

Recreate missing CSRs:

A missing CSR can be generated from an existing certificate. To regenerate the CA's CSR run this command:

cd /etc/puppetlabs/puppet/ssl/ca
openssl x509 -x509toreq -in ca_crt.pem -signkey ca_key.pem -out ca_csr.pem

The procedure for generating the puppet *server* certificate is similar however you will need to follow these steps to ensure the proper SANs are included.

Note, that those requests aren’t perfect: the certificate CA extensions are missing, but we’ll fill them in during the next step.

Sign your new CSRs:

Next, we generate new certificates from the existing private key and the signing request. To get the necessary X509v3 extensions into the CA certificate, we first create a suitable OpenSSL config file snippet:

cat > extension.cnf <<_EOT_
[CA_extensions]
basicConstraints = critical,CA:TRUE
nsComment = "Puppet Ruby/OpenSSL Internal Certificate"
keyUsage = critical,keyCertSign,cRLSign
subjectKeyIdentifier = hash
_EOT_

Sign your CSR using this configuration.

cp ca_crt.pem ca_crt.pem.backup
openssl x509 -req -days 3650 -in ca_csr.pem -signkey ca_key.pem -out ca_crt.pem -extfile extension.cnf -extensions CA_extensions

Now use the new CA cert to regenerate the puppet master's certificate.

cp /etc/pki/tls/openssl.cnf /tmp/openssl.cnf
export sans="[SAN]\nsubjectAltName=DNS:puppet.example.com,DNS:puppet\n"
printf $sans >> /tmp/openssl.cnf
openssl req -new -sha256 -key ../private_keys/puppetmaster.example.com.pem -reqexts SAN -config /tmp/openssl.cnf -out requests/puppetmaster.example.com.pem
openssl x509 -req -days 3650 -in requests/puppetmaster.example.com.pem -CA ca_crt.pem -CAkey ca_key.pem -CAserial serial -out signed/puppetmaster.example.com.pem

You can also use the "puppet cert command":

puppet cert sign --allow-dns-alt-names puppetmaster.example.com

After the cert has been signed copy the cert into place and restart puppetserver.

cp signed/puppetmaster.example.com.pem /etc/puppetlabs/puppet/ssl/certs/puppetmaster.example.com.pem
systemctl restart puppetserver

Distribute the CA certificate

Puppet clients need the CA certificate to be locally available so that they can verify other certificates against it. We copy the newly generated ca_crt.pem into some Puppet module and let Puppet place it on all clients:

file { '/etc/puppetlabs/puppet/ssl/certs/ca.pem': 
  source => 'puppet:///path/to/ca_crt.pem', 
  owner => 'puppet', 
  group => 'puppet', 
}

That’s it! No more warnings, everyone happy. 🙂