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Encrypting PXC Traffic

There are two kinds of traffic in Percona XtraDB Cluster:

  1. Client-Server traffic (the one between client applications and cluster nodes).

  2. Replication traffic, that includes SST, IST, write-set replication, and various service messages.

    Percona XtraDB Cluster supports encryption for all types of traffic. Replication traffic encryption can be configured either in automatic or in manual mode.

Encrypting Client-Server Communication

Percona XtraDB Cluster uses the underlying MySQL encryption mechanism to secure communication between client applications and cluster nodes.

Specify the following settings in the my.cnf configuration file for each node:



After restart the node will use these files to encrypt communication with clients. MySQL clients require only the second part of the configuration to communicate with cluster nodes.

Starting from the version 5.7, MySQL generates default key and certificate files and places them in data directory. You can either use them or generate new certificates. For generation of new certificate please refer to Generating Keys and Certificates Manually section.

Encrypting Replication Traffic

Replication traffic refers to the inter-node traffic which includes SST traffic, IST traffic, and replication traffic.

Traffic of each type is transferred via different channel, and so it is important to configure secure channels for all 3 variants to completely secure the replication traffic.

Starting from 5.7, PXC supports a single configuration option which helps to secure complete replication traffic, and is often referred as Automatic Configuration. User can also ignore this and configure security of each channel by specifying independent parameters.

Section below will help, covering this aspect.

SSL Automatic Configuration

Enabling pxc-encrypt-cluster-traffic

Percona XtraDB Cluster includes the pxc-encrypt-cluster-traffic variable that enables automatic configuration of SSL encryption there-by encrypting SST, IST, and replication traffic.

This variable is not dynamic and so cannot be changed on runtime. To enable automatic configuration of SSL encryption, set pxc-encrypt-cluster-traffic=ON in the the [mysqld] section of the my.cnf file, and restart the cluster (by default it is disabled there-by using non-secured channel for replication).


Setting pxc-encrypt-cluster-traffic=ON has effect of applying the following settings in my.cnf configuration file:



For wsrep_provider_options, only the mentioned options are affected (socket.ssl_key, socket,ssl_cert, and socket.ssl_ca), the rest is not modified.

Automatic configuration of the SSL encryption needs key and certificate files. Starting from the version 5.7, MySQL generates default key and certificate files and places them in data directory. These auto-generated files are suitable for automatic SSL configuration, but you should use the same key and certificate files on all nodes. Also you can override auto-generated files with manually created ones, as covered by the Generating Keys and Certificates Manually section.

Necessary key and certificate files are first searched at the ssl-ca, ssl-cert, and ssl-key options under [mysqld]. If these options are not set, it then looks in the data directory for ca.pem, server-cert.pem, and server-key.pem files.


The [sst] section is not searched.

If all three files are found, they are used to configure encryption. If any of the files is missing, a fatal error is generated.

SSL Manual Configuration

If user wants to enable encryption for specific channel only or use different certificates or other mix-match, then user can opt for manual configuration. This helps to provide more flexibility to end-users.

To enable encryption manually, the location of the required key and certificate files shoud be specified in the Percona XtraDB Cluster configuration. If you do not have the necessary files, see Generating Keys and Certificates Manually.


Encryption settings are not dynamic. To enable it on a running cluster, you need to restart the entire cluster.

There are three aspects of Percona XtraDB Cluster operation, where you can enable encryption:

This refers to SST traffic during full data copy from one cluster node (donor) to the joining node (joiner).

This refers to all internal Percona XtraDB Cluster communication, such as, write-set replication, IST, and various service messages.

Encrypting SST Traffic

This refers to full data transfer that usually occurs when a new node (JOINER) joins the cluster and receives data from an existing node (DONOR).

For more information, see State Snapshot Transfer.


If keyring_file plugin is used, then SST encryption is mandatory: when copying encrypted data via SST, the keyring must be sent over with the files for decryption. In this case following options are to be set in my.cnf on all nodes:

The cluster will not work if keyring configuration across nodes is different.

The following SST methods are available: xtrabackup, rsync, and mysqldump.


This is the default SST method (the wsrep_sst_method is set to xtrabackup-v2), which uses Percona XtraBackup to perform non-blocking transfer of files. For more information, see Percona XtraBackup SST Configuration.

Encryption mode for this method is selected using the encrypt option:

  • encrypt=0 is the default value, meaning that encryption is disabled.

  • encrypt=1, encrypt=2, and encrypt=3 have been deprecated.

  • encrypt=4 enables encryption based on key and certificate files generated with OpenSSL. For more information, see Generating Keys and Certificates Manually.

To enable encryption for SST using XtraBackup, specify the location of the keys and certificate files in the each node’s configuration under [sst]:



SSL clients require DH parameters to be at least 1024 bits, due to the logjam vulnerability. However, versions of socat earlier than 1.7.3 use 512-bit parameters. If a dhparams.pem file of required length is not found during SST in the data directory, it is generated with 2048 bits, which can take several minutes. To avoid this delay, create the dhparams.pem file manually and place it in the data directory before joining the node to the cluster:

openssl dhparam -out /path/to/datadir/dhparams.pem 2048

For more information, see this blog post.


This SST method does not support encryption. Avoid using this method if you need to secure traffic between DONOR and JOINER nodes. If you using keyring plugin then keyring file needs to be send over from DONOR to JOINER. Avoid using this method in such cases too.


This SST method dumps data from DONOR and imports it to JOINER. Encryption in this case is performed using the same certificates configured for Encrypting Client-Server Communication, because mysqldump connects through the database client.

Here is how to enable encryption for SST using mysqldump in a running cluster:

  1. Create a user for SST on one of the nodes:

    mysql> CREATE USER 'sstuser'$'%' IDENTIFIED BY PASSWORD 'sst_password';


    This user must have the same name and password on all nodes where you want to use mysqldump for SST.

  2. Grant usage privileges to this user and require SSL:

    mysql> GRANT USAGE ON *.* TO 'sstuser' REQUIRE SSL;
  3. To make sure that the SST user replicated across the cluster, run the following query on another node:

    mysql> SELECT User, Host, ssl_type FROM mysql.user WHERE User='sstuser';

    The example of the output is the following:

    | User     | Host | ssl_type |
    | sstuser | %    | Any      |


    If the wsrep_OSU_method is set to ROI, you need to manually create the SST user on each node in the cluster.

  4. Specify corresponding certificate files in both [mysqld] and [client] sections of the configuration file on each node:


    For more information, see Encrypting Client-Server Communication.

  5. Also specify the SST user credentials in the wsrep_sst_auth variable on each node:

    wsrep_sst_auth = sstuser:sst_password
  6. Restart the cluster with the new configuration.

    If you do everything correctly, mysqldump will connect to DONOR with the SST user, generate a dump file, and import it to JOINER node.

Encrypting Replication/IST Traffic

Replication traffic refers to the following:

  • Write-set replication which is the main workload of Percona XtraDB Cluster (replicating transactions that execute on one node to all other nodes).

  • Incremental State Transfer (IST) which is copying only missing transactions from DONOR to JOINER node.

  • Service messages which ensure that all nodes are synchronized.

All this traffic is transferred via the same underlying communication channel (gcomm). Securing this channel will ensure that IST traffic, write-set replication, and service messages are encrypted. (For IST, a separate channel is configured using the same configuration parameters, so 2 sections are described together).

To enable encryption for all these processes, define the paths to the key, certificate and certificate authority files using the following wsrep provider options:

To set these options, use the wsrep_provider_options variable in the configuration file:



You must use the same key and certificate files on all nodes, preferably those used for Encrypting Client-Server Communication.

Check the Upgrading Certificates section on how to upgrade existing certificates.

Generating Keys and Certificates Manually

As mentioned above, MySQL generates default key and certificate files and places them in data directory. If user wants to override these certificates, the following new sets of files can be generated:

  • Certificate Authority (CA) key and certificate to sign the server and client certificates.

  • Server key and certificate to secure database server activity and write-set replication traffic.

  • Client key and certificate to secure client communication traffic.

These files should be generated using OpenSSL.


The Common Name value used for the server and client keys and certificates must differ from that value used for the CA certificate.

Generating CA Key and Certificate

The Certificate Authority is used to verify the signature on certificates.

  1. Generate the CA key file:

    $ openssl genrsa 2048 > ca-key.pem
  2. Generate the CA certificate file:

    $ openssl req -new -x509 -nodes -days 3600
        -key ca-key.pem -out ca.pem

Generating Server Key and Certificate

  1. Generate the server key file:

    $ openssl req -newkey rsa:2048 -days 3600 \
        -nodes -keyout server-key.pem -out server-req.pem
  2. Remove the passphrase:

    $ openssl rsa -in server-key.pem -out server-key.pem
  3. Generate the server certificate file:

    $ openssl x509 -req -in server-req.pem -days 3600 \
        -CA ca.pem -CAkey ca-key.pem -set_serial 01 \
        -out server-cert.pem

Generating Client Key and Certificate

  1. Generate the client key file:

    $ openssl req -newkey rsa:2048 -days 3600 \
        -nodes -keyout client-key.pem -out client-req.pem
  2. Remove the passphrase:

    $ openssl rsa -in client-key.pem -out client-key.pem
  3. Generate the client certificate file:

    $ openssl x509 -req -in client-req.pem -days 3600 \
       -CA ca.pem -CAkey ca-key.pem -set_serial 01 \
       -out client-cert.pem

Verifying Certificates

To verify that the server and client certificates are correctly signed by the CA certificate, run the following command:

$ openssl verify -CAfile ca.pem server-cert.pem client-cert.pem

If the verification is successful, you should see the following output:

server-cert.pem: OK
client-cert.pem: OK

Failed validation caused by matching CN

Sometimes, an SSL configuration may fail if the certificate and the CA files contain the same .

To check if this is the case run openssl command as follows and verify that the CN field differs for the Subject and Issuer lines.

$ openssl x509 -in server-cert.pem -text -noout

To obtain a more compact output run openssl specifying -subject and -issuer parameters:

$ openssl x509 -in server-cert.pem -subject -issuer -noout

Deploying Keys and Certificates

Use a secure method (for example, scp or sftp) to send the key and certificate files to each node. Place them under the /etc/mysql/certs/ directory or similar location where you can find them later.


Make sure that this directory is protected with proper permissions. Most likely, you only want to give read permissions to the user running mysqld.

The following files are required:

  • Certificate Authority certificate file (ca.pem)

This file is used to verify signatures.

  • Server key and certificate files (server-key.pem and server-cert.pem)

These files are used to secure database server activity and write-set replication traffic.

  • Client key and certificate files (client-key.pem and client-cert.pem)

These files are required only if the node should act as a MySQL client. For example, if you are planning to perform SST using mysqldump.


Upgrading Certificates subsection covers the details on upgrading certificates, if necessary.

Upgrading Certificates

The following procedure shows how to upgrade certificates used for securing replication traffic when there are two nodes in the cluster.

  1. Restart the first node with the socket.ssl_ca option set to a combination of the the old and new certificates in a single file.

    For example, you can merge contents of old-ca.pem and new-ca.pem into upgrade-ca.pem as follows:

    cat old-ca.pem > upgrade-ca.pem && \
    cat new-ca.pem >> upgrade-ca.pem

    Set the wsrep_provider_options variable as follows:

  2. Restart the second node with the socket.ssl_ca, socket.ssl_cert, and socket.ssl_key options set to the corresponding new certificate files.

  3. Restart the first node with the new certificate files, as in the previous step.

  4. You can remove the old certificate files.