socat tunnel for encrypted rsync SST

wsrep_sst_rsync_tunnel is an extension of the rsync-based SST implementation that ships with mariadb. Its purpose is to encrypt communication between the donor and the joiner during an SST.

Encryption is implemented by means of a socat tunnel, using OPENSSL addresses. It can be configured via the regular openssl flags exposed by socat.

How to configure the script

This SST script can configured by setting a few keys in your favorite mariadb option file in addition to the usual galera settings.

[mysqld]
...
bind_address=<node-name>
wsrep_sst_method=rsync_tunnel
...

[sst]
tca=/path/to/your/ca-file.crt
tcert=/path/to/node/certificate.crt
tkey=/path/to/node/key.key
sockopt=<openssl-address-options-as-per-socat-manual>

When a joiner node requests an SST, wsrep_sst_rsync_tunnel uses socat to listen to incoming SSL connections on port 4444 in lieu of the original rsync daemon. Received data will be forwarded to the rscynd daemon started locally to replicate the database.

When a donor node serves the SST, wsrep_sst_rsync_tunnel makes a series of rsync calls that target a locally started socat daemon. The daemon tunnels all rsync traffic into an encrypted SSL connection that targets the joiner's end of the socat tunnel.

Encryption parameters are specified under the [sst] group in the mariadb option file, where tkey and tcert are respectively the key and the certificate that are used by both sides of the socat tunnel. Each node typically has a different key and cert. Both key and certificate can be combined into a single PEM file and referenced by tcert. Option tca holds a list of the trusted signing certificates.

In case you need to tweak the creation of the SSL connection, you can pass valid socat options (as per socat manual) via the sockopt key. For debugging purpose, the exact socat command that is being executed shows up in the mariadb log file.

Note that socat verifies that the certificate's commonName matches that of the host that is being targeted. The target name comes from the value configured in bind_address, so it's important that it matches the certificate's commonName. An IP address can be used for bind_address, but you may get into trouble in case different hostnames resolve to the same IP (e.g. multiple networks per host).

Examples of use

Suppose you're running a 3-node galera cluster node1.my.cluster, node2.my.cluster, node3.my.cluster.

Scenario: using self-signed certificates

On each node, create a key and a certificate, and bundle them into a single PEM file. For instance on node1.my.cluster:

openssl genrsa -out /tls/mysql-$(hostname -f).key 2048
openssl req -new -key /tls/mysql-$(hostname -f).key -x509 -days 365000 -subj "/CN=$(hostname -f)" -out /tls/mysql-$(hostname -f).crt -batch
cat /tls/mysql-$(hostname -f).key /tls/mysql-$(hostname -f).crt > /tls/mysql.pem

Then, on each node, create a cafile that will contain all the certs to trust:

for n in node1.my.cluster node2.my.cluster node3.my.cluster; do
   ssh $n 'cat /tls/mysql-$(hostname -f).crt' >> /tls/all-mysql.crt
done

Once you have those two files on each host, you can configure the SST appropriately. For instance from /etc/my.cnf.d/galera.cnf:

[mysqld]
...

[sst]
tca=/tls/all-mysql.crt
tcert=/tls/mysql.pem

Scenario: using self-signed certificates, without verification

By default, when socat tries to establish a SSL connection to a peer, it also verifies that it can trust the peer's certificate. If for some reason you need to disable that feature, you can amend the previous configuration with a sockopt option:

[mysqld]
...

[sst]
tca=/tls/all-mysql.crt
tcert=/tls/mysql.pem
sockopt="verify=0"

The associated sockopt value is passed to socat when the donor or the joiner configures his part of the tunnel.

Note: please do not do so in production, this is inherently insecure as you will not verify the identity of the peer you're connecting to!

Scenario: using certificates from a CA

Suppose you have a FreeIPA service which generated a key file and a certificate file for the three galera nodes, respectively located at /tls/mysql.key and /tls/mysql.crt.

Assuming that the certificate for the FreeIPA server is available at /etc/ipa/ca.crt, you can configure you galera servers as follows:

[sst]
tca=/etc/ipa/ca.crt
tcert=/tls/mysql.crt
tkey=/tls/mysql.key

apevec/wsrep_sst_rsync_tunnel