TLS certificate setup

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Pacemaker optionally supports encrypting communications with TLS certificates for two things:

1. Pacemaker Remote node connections
2. Remote CIB operations (CIB_user=... CIB_encrypted=... CIB_port=... cibadmin -Q)

This is especially important for remote CIB operations which have no encryption at all otherwise.

Testing this requires a fair bit of setup. We assume that users will use TLS certificates as follows:

• They will set up their own Certificate Authority (CA). In the real world, you pay a real CA a lot of money to sign your credentials. This is because web browsers have lists of CAs they trust, and so if you use one of those then your credentials will be trusted. Otherwise the user will get a scary error about self-signed certificates and things like that. However, we expect that people will keep their clusters on private networks and connect via our own command line tools, so there's no real need for a trusted, real CA.

• They will generate one set of credentials for each server. If they have ten Pacemaker Remote nodes (remember - remote nodes are the server, the cluster is the client) then each would have its own server cert and key.

• They will generate one set of credentials for each client. If they have ten admin machines that need to run cibadmin to do remote CIB operations, then each would have its own client cert and key. This makes it possible to revoke a single client's credentials if necessary without a lot of annoying work.

In addition, this document will assume there is not an intermediate CA involved. In the real world, you would create a root CA and only use that to sign credentials for intermediate CAs. The intermediate CA would then sign the client/server credentials. The reason for this is that if your CA gets compromised, everything it has ever signed is now compromised as well. The root CA credentials would be locked away and only taken out on the rare time when you need a new intermediate. Pacemaker should support this just fine as long as the root CA and intermediate CA credentials get bundled together. I'm not going to cover how to do that here.

If you look around, you'll find tons of explanations for how to set this stuff up. These instructions worked for me. There very well may be much simpler ways to do all of this.

To generate TLS credentials, you need to do all of the following...

Create your own CA

Set up the directory structure

$ mkdir -p ~/cert-stuff/ca/{certs,newcerts,private,csr}
$ mkdir -p ~/cert-stuff/{clients,servers}
$ cd ~/cert-stuff/ca
$ echo 01 > serial
$ echo 01 > crlnumber
$ touch index.txt

Create openssl.cnf

If you don't create your own config file and specify it on the openssl command line, it will default to using /etc/pki/tls/openssl.cnf. This may or may not be what you want. So, we'll create our own just to make sure everything is explicitly defined. Much of this is largely just boilerplate. However, pay attention to the dir setting and the default values in req_distinguished_name.

[ ca ]
# Use the options from the CA_default section
default_ca = CA_default


[ CA_default ]
# Directory and file locations.
dir               = /root/cert-stuff/ca
certs             = $dir/certs
crl_dir           = $dir/crl
new_certs_dir     = $dir/newcerts
database          = $dir/index.txt
serial            = $dir/serial
RANDFILE          = $dir/private/.rand

# The root key and root certificate.
private_key       = $dir/private/ca.key.pem
certificate       = $dir/certs/ca.cert.pem

# For certificate revocation lists.
crlnumber         = $dir/crlnumber
crl               = $dir/crl/ca.crl.pem
crl_extensions    = crl_ext
default_crl_days  = 30

# SHA-1 is deprecated, so use SHA-2 instead.
default_md        = sha256

# Formatting option for names
name_opt          = ca_default
# Certificate output options
cert_opt          = ca_default
# Default certificate validity
default_days      = 375
# Preserve existing extensions
preserve          = no
# Certificate policy section
policy            = policy_strict


# Policy section to use for validating root CA signatures

[ policy_strict ]
countryName             = match
stateOrProvinceName     = match
organizationName        = match
organizationalUnitName  = optional
commonName              = supplied
emailAddress            = optional


# Options to apply when creating certs or CSRs

[ req ]
default_bits        = 2048
distinguished_name  = req_distinguished_name
string_mask         = utf8only

# SHA-1 is deprecated, so use SHA-2 instead.
default_md          = sha256

# Extension to add when the -x509 option is used.
x509_extensions     = v3_ca


# Information required in a CSR, with optional defaults

[ req_distinguished_name ]
countryName                     = Country Name (2 letter code)
stateOrProvinceName             = State or Province Name
localityName                    = Locality Name
0.organizationName              = Organization Name
organizationalUnitName          = Organizational Unit Name
commonName                      = Common Name
emailAddress                    = Email Address

# Optionally, specify some defaults.
countryName_default             = US
stateOrProvinceName_default     = NH
localityName_default            = Merrimack
0.organizationName_default      = Cluster
#organizationalUnitName_default =
#emailAddress_default           =


# Options that are applied when `-extensions v3_ca` is given when creating
# the root certificate

[ v3_ca ]
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid:always,issuer
basicConstraints = critical, CA:true
keyUsage = critical, digitalSignature, cRLSign, keyCertSign


# Options that are applied when `-extensions server_cert` is given when signing
# server certificates

[ server_cert ]
basicConstraints = CA:FALSE
nsCertType = server
nsComment = "OpenSSL Generated Server Certificate"
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer:always
keyUsage = critical, digitalSignature, keyEncipherment
extendedKeyUsage = serverAuth


# Options that are applied when `-extensions client_cert` is given when signing
# client certificates

[ client_cert ]
basicConstraints = CA:FALSE
nsCertType = client, email
nsComment = "OpenSSL Generated Client Certificate"
subjectKeyIdentifier = hash
authorityKeyIdentifier = keyid,issuer
keyUsage = critical, nonRepudiation, digitalSignature, keyEncipherment
extendedKeyUsage = clientAuth, emailProtection


# Options that are applied when creating CRLs

[ crl_ext ]
authorityKeyIdentifier = keyid:always

Generate the root CA certificate

Set days to something appropriate - this is how many days until the root CA expires. For testing, shorter is fine. For real world use, make it very long. When the root CA expires, everything it signed expires too. Years would be appropriate. You can optionally provide -subj on the command line, but if you don't, openssl will prompt you for this information.

$ openssl genrsa -out private/ca.key.pem 4096
$ chmod 400 private/ca.key.pem
$ openssl req -config openssl.cnf -key private/ca.key.pem -new -x509 -days 100 -sha256 -extensions v3_ca -out certs/ca.cert.pem
$ chmod 444 certs/ca.cert.pem

Installation

For real world use, keep the private ca.key.pem file private. Set ownership and permissions restrictively. Maybe store it on a USB key instead of permanently on the system. The ca.cert.pem file should be installed to every client and server system and readable by the cluster user (hacluster:haclient most likely). This file should also be referenced in /etc/sysconfig/pacemaker as PCMK_ca_file.

Generate server stuff

For each server (Pacemaker Remote node or hosts that you want to be able to access via cibadmin) do the following:

Generate private key and Certificate Signing Request (CSR)

Replace <servername> with the hostname (not FQDN) of the server. You can name it whatever you want, actually, but using the hostname makes keeping track of these things easier if there's a bunch of them.

$ openssl genrsa -out ../servers/<servename>.key.pem 4096
$ chmod 400 ../servers/<servername>.key.pem
$ openssl req -config openssl.cnf -new -key ../servers/<servername>.key.pem -out ../servers/<servername>.csr

Answer any questions openssl asks. If it asks for a passphrase, don't provide one. This has not been tested yet and it's likely the cluster will hang asking for the passphrase when it tries to read the key. When it asks for a Common Name, use the FQDN of the server. Note that the server's Common Name cannot be the same as the root CA's Common Name.

Create and sign the server certificate

Again, change <servername> to the hostname and set days to something that makes sense.

$ openssl ca -config openssl.cnf -extensions server_cert -days 100 -notext -md sha256 -in ../servers/<servername>.csr -out ../servers/<servername>.cert.pem
$ chmod 444 ../servers/<servername>.cert.pem

Installation

Copy <servername>.cert.pem and <servername>.key.pem to the server. Both should be owned by the cluster user (hacluster:haclient most likely). The key should only be readable by the cluster user. I think it's okay if the cert is world-readable. These files should also be referenced in /etc/sysconfig/pacemaker as PCMK_cert_file and PCMK_key_file.

Generate client stuff

Everything is exactly the same on clients, except the paths will be different and there's a different extension to use. I'm not going to cover any of this in depth, just list the commands. Refer to the server section for details.

Generate private key and CSR

$ openssl genrsa -out ../clients/<clientname>.key.pem 4096
$ chmod 400 ../clients/<clientname>.key.pem
$ openssl req -config openssl.cnf -new -key ../clients/<clientname>.key.pem -out ../clients/<clientname>.csr

For clients, the Common Name should be something like an email address.

Create and sign the client certificate

$ openssl ca -config openssl.cnf -extensions client_cert -days 100 -notext -md sha256 -in ../clients/<clientname>.csr -out ../clients/<clientname>.cert.pem
$ chmod 444 ../clients/<clientname>.cert.pem

Installation

Installation of the client side is the same as the server side.

Revoking a certificate

If one of the admin machines used to access the CIB remotely is compromised, stolen, or can otherwise not be trusted, a Certificate Revocation List can be used to tell cluster machines to no longer allow use of that certificate. It's also possible to revoke the certificate of a server to prevent clients from accessing a potentially compromised server. In both cases, the commands are the same.

$ openssl ca -config openssl.cnf -gencrl -out crl/rootca.crl
$ openssl ca -config openssl.cnf -revoke ../<clients/servers>/<name>.cert.pem

CRLs should be regenerated frequently (according to the config file's default_crl_days setting, they expire in 30 days) and distributed to all clients and servers.

Having done all that, using it is a lot less complicated. Pacemaker Administration and Pacemaker Explained cover this in more depth, but the quick explanation is:

• For remote CIB operations, the admin machine is the client and the cluster machine is the server. Make sure the server has the server credentials and they are listed in /etc/sysconfig/pacemaker. Command line tools (like cibadmin, most commonly used for remote CIB operations) do not read the sysconfig file so all the credentials must be passed by the environment. Note that in addition to the TLS parameters, you must still give a username and password. See Pacemaker Administration for more details.

• For Pacemaker Remote nodes, the cluster machine running the remote resource is the client and the system running pacemaker_remoted is the server. Here, both sides are running a daemon so make sure the appropriate credentials are listed in /etc/sysconfig/pacemaker on both ends of the connection. There is no need to pass anything in the environment.