Configuration¶

Firewall¶

Galera Cluster requires that you open the following ports to network traffic:

• On 3306, Galera Cluster uses TCP for database client connections and State Snapshot Transfers methods that require the client, (that is, mysqldump).
• On 4567, Galera Cluster uses TCP for replication traffic. Multicast replication uses both TCP and UDP on this port.
• On 4568, Galera Cluster uses TCP for Incremental State Transfers.
• On 4444, Galera Cluster uses TCP for all other State Snapshot Transfer methods.

This can be achieved using the iptables command:

# iptables --append INPUT --in-interface eth0 \
  --protocol tcp --match tcp --dport ${PORT} \
  --source ${NODE-IP-ADDRESS} --jump ACCEPT

Make sure to save the changes once you are done. This will vary depending on your distribution:

• For Ubuntu
• For Fedora

Alternatively, make modifications using the firewall-cmd utility for FirewallD that is available on many Linux distributions:

# firewall-cmd --add-service=mysql --permanent
# firewall-cmd --add-port=3306/tcp --permanent

SELinux¶

Security-Enhanced Linux is a kernel module for improving security on Linux operating systems. It is commonly enabled and configured by default on Red Hat-based distributions. In the context of Galera Cluster, systems with SELinux may block the database service, keep it from starting, or prevent it from establishing network connections with the cluster.

To configure SELinux to permit Galera Cluster to operate, you may need to use the semanage utility to open the ports it uses. For example:

# semanage port -a -t mysqld_port_t -p tcp 3306

Older versions of some distributions, which do not have an up-to-date policy for securing Galera, may also require SELinux to be more relaxed about database access and actions:

# semanage permissive -a mysqld_t

AppArmor¶

Application Armor is a kernel module for improving security on Linux operating systems. It is developed by Canonical and commonly used on Ubuntu-based distributions. In the context of Galera Cluster, systems with AppArmor may block the database service from operating normally.

To configure AppArmor to work with Galera Cluster, complete the following steps on each cluster node:

1. Create a symbolic link for the database server in the disable directory:

   # ln -s /etc/apparmor.d/usr /etc/apparmor.d/disable/.sbin.mysqld
   

2. Restart AppArmor. For servers that use init, run the following command:

   # service apparmor restart
   

   For servers that use systemd, run the following command:

   # systemctl restart apparmor
   

AppArmor now permits Galera Cluster to operate.

Configuring mysqld¶

While all of the configuration parameters available to the standard MySQL, MariaDB, or Percona XtraDB database servers are available in Galera Cluster, there are some that you must define an outset to avoid conflict or unexpected behavior.

• Ensure that the database server is not bound only to the localhost: 127.0.0.1. Also, do not bind it to 0.0.0.0. Binding to the localhost or 0.0.0.0 makes mySQL bind to all IP addresses on the machine, including the virtual IP address causing HAProxy not to start. Instead, bind to the management IP address of the controller node to enable access by other nodes through the management network:

  bind-address=10.0.0.12
  

• Ensure that the binary log format is set to use row-level replication, as opposed to statement-level replication:

  binlog_format=ROW
  

Configuring InnoDB¶

Galera Cluster does not support non-transactional storage engines and requires that you use InnoDB by default. There are some additional parameters that you must define to avoid conflicts.

• Ensure that the default storage engine is set to InnoDB:

  default_storage_engine=InnoDB
  

• Ensure that the InnoDB locking mode for generating auto-increment values is set to 2, which is the interleaved locking mode:

  innodb_autoinc_lock_mode=2
  

  Do not change this value. Other modes may cause INSERT statements on tables with auto-increment columns to fail as well as unresolved deadlocks that leave the system unresponsive.

• Ensure that the InnoDB log buffer is written to file once per second, rather than on each commit, to improve performance:

  innodb_flush_log_at_trx_commit=0
  

  Setting this parameter to 1 or 2 can improve performance, but it introduces certain dangers. Operating system failures can erase the last second of transactions. While you can recover this data from another node, if the cluster goes down at the same time (in the event of a data center power outage), you lose this data permanently.

• Define the InnoDB memory buffer pool size. The default value is 128 MB, but to compensate for Galera Cluster’s additional memory usage, scale your usual value back by 5%:

  innodb_buffer_pool_size=122M
  

Configuring wsrep replication¶

Galera Cluster configuration parameters all have the wsrep_ prefix. You must define the following parameters for each cluster node in your OpenStack database.

• wsrep Provider: The Galera Replication Plugin serves as the wsrep provider for Galera Cluster. It is installed on your system as the libgalera_smm.so file. Define the path to this file in your my.cnf:

  wsrep_provider="/usr/lib/libgalera_smm.so"
  

• Cluster Name: Define an arbitrary name for your cluster.

  wsrep_cluster_name="my_example_cluster"
  

  You must use the same name on every cluster node. The connection fails when this value does not match.

• Cluster Address: List the IP addresses for each cluster node.

  wsrep_cluster_address="gcomm://192.168.1.1,192.168.1.2,192.168.1.3"
  

  Replace the IP addresses given here with comma-separated list of each OpenStack database in your cluster.

• Node Name: Define the logical name of the cluster node.

  wsrep_node_name="Galera1"
  

• Node Address: Define the IP address of the cluster node.

  wsrep_node_address="192.168.1.1"
  

SHOW VARIABLES LIKE 'wsrep_%';

+------------------------------+-------+
| Variable_name                | Value |
+------------------------------+-------+
| wsrep_auto_increment_control | ON    |
+------------------------------+-------+
| wsrep_causal_reads           | OFF   |
+------------------------------+-------+
| wsrep_certify_nonPK          | ON    |
+------------------------------+-------+
| ...                          | ...   |
+------------------------------+-------+
| wsrep_sync_wait              | 0     |
+------------------------------+-------+