Setup AWS MySQL 5.6 Aurora as a Slave for an external Master with SSL

Setting up Aurora as a slave for an external MySQL server that acts as the master is a bit tricky. Of course we want a secured connection. For this reason we need to create client certificates to be used by AWS RDS. The steps below should work for RDS as well. 

Generate and Sign  the Certificates

The process is actually simple, but AWS is picky how you generate the certificates. I was using a SHA flag that was accepted by a regular MySQL 5.6 instance, but caused a cryptic (pun intended) MySQL 2026 Generic SSL error and it was quite hard to find the source.  Also note that you need to have different common names (CN) for all three certificate pairs. They do not necessarily need to fit the actual domain name, but they need to be different. 

First we need to create the certificate authority that can sign the keys

# Generate a certificate authority key pair
openssl genrsa 2048 > ca-key.pem
# Notice the CN name. It needs to be different for all of the three key pairs that we create!
openssl req -new -x509 -nodes -days 3600 -key ca-key.pem -out ca.pem -subj "/C=AT/ST=Tirol/L=Innsbruck/O=The Good Corp/OU=IT Department/CN=ca.mysql"

Then create the server key pair

#Generate a server key. Note again the different CN
openssl req -newkey rsa:2048 -days 3600 -nodes -keyout server-key.pem -out server-req.pem -subj "/C=AT/ST=Tirol/L=Innsbruck/O=The Good Corp/OU=IT Department/CN=server.mysql"
# Convert the format
openssl rsa -in server-key.pem -out server-key.pem
# Sign it
openssl x509 -req -in server-req.pem -days 3600 -CA ca.pem -CAkey ca-key.pem -set_serial 01 -out server-cert.pem

Finally we generate a client certificate and its key. You can repeat these steps to generate multiple certificates for clients

# Again, note the CN
openssl req -newkey rsa:2048 -days 3600 -nodes -keyout client-key.pem -out client-req.pem -subj "/C=AT/ST=Tirol/L=Innsbruck/O=The Good Corp/OU=IT Department/CN=client.mysql"
# Convert
openssl rsa -in client-key.pem -out client-key.pem
# Sign
openssl x509 -req -in client-req.pem -days 3600 -CA ca.pem -CAkey ca-key.pem -set_serial 01 -out client-cert.pem
# Verify
openssl verify -CAfile ca.pem server-cert.pem client-cert.pem

Now we have all the certs we need.

Master Setup

The setup is pretty standard. Add the server certificates to the MySQL configuration of your master and restart.

# SSL Server Certificate
ssl-ca=/etc/mysql/ssl/ca.pem
ssl-cert=/etc/mysql/ssl/server-cert.pem
ssl-key=/etc/mysql/ssl/server-key.pem

Then create a user for the slave

CREATE USER 'aws'@'%' IDENTIFIED BY 'SECRET';
GRANT REPLICATION CLIENT, REPLICATION SLAVE ON *.* TO 'aws'@'%' IDENTIFIED BY 'SECRET' REQUIRE SSL;

Slave Setup

On AWS you do not have SUPER() privileges, but can use stored procedures provided by Amazon to setup the slave.

Start fresh by removing old records. If there was no previous setup, there might be an error.

CALL mysql.rds_remove_binlog_ssl_material;
CALL mysql.rds_reset_external_master;

Now you need to pass the client certificate data as a JSON to AWS Aurora.

CALL mysql.rds_import_binlog_ssl_material('{"ssl_ca":"-----BEGIN CERTIFICATE-----
MIIBAgMBVRpcm9sMRIw...
...
-----END CERTIFICATE-----\n","ssl_cert":"-----BEGIN CERTIFICATE-----
KAoIBAQCzn28awhyN8V56Z2bskCiMhJt4
...
-----END CERTIFICATE-----\n","ssl_key":"-----BEGIN RSA PRIVATE KEY-----
SbeLNsRzrPoCVGGqwqR6gE6AZu
...
-----END RSA PRIVATE KEY-----"}');

A message that the SSL data was accepted will appear if you pasted the certificate, the key and the CA certificate correctly.

Finally, start the replication and check the status

CALL mysql.rds_start_replication;
SHOW SLAVE STATUS\G

Tests and Troubleshooting

On the master, you can check if the slave even tries to connect for instance with tcpdump. In the example below the IP 1.2.3.4 would be the AWS gateway address as seen by your firewall.

sudo tcpdump src host 1.2.3.4 -vv

 

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