Template:OXLoadBalancingClustering Database

Overview

You can choose between Galera or two-sided Master/Slave ("Master/Master") replication.

Galera database setup

OX only supports the "Percona XtraDB Cluster 5.5" flavor of the Galera database.

Installation

Debian systems

The following has been adjusted to work with Wheezy, but works similar with Squeeze, only the repo paths need adjustments.

To install the software, we first need to configure the repository and its build key, update our sources lists and install the packages:

gpg --keyserver  hkp://keys.gnupg.net --recv-keys 1C4CBDCDCD2EFD2A
gpg -a --export CD2EFD2A | apt-key add -

cat >/etc/apt/sources.list.d/percona.list <<EOF
deb http://repo.percona.com/apt wheezy main
deb-src http://repo.percona.com/apt wheezy main
EOF

apt-get update
apt-get install percona-xtradb-cluster-client-5.5 percona-xtradb-cluster-server-5.5 percona-xtrabackup

RHEL 6 systems

Should also apply to CentOS 6.

First, disable selinux, iptables, ip6tables. (Galera does not run with selinux. Using iptables and ip6tables should work if you configure it correctly, but documentation thereof is out of scope of this document.) Reboot.

Percona XtraDB Cluster relies on socat which is not shipped by RHEL. We need to install from a different source. The epel repository can be used for that.

yum install epel-release

The installation command itself needs to be a composite remove, install command since yum is not clever enough to resolve the conflicts itself, so we need to tell it how.

wget http://www.percona.com/downloads/percona-release/percona-release-0.0-1.x86_64.rpm
yum localinstall percona-release-0.0-1.x86_64.rpm

yum shell
remove mysql-libs
install Percona-XtraDB-Cluster-server-55 Percona-XtraDB-Cluster-client-55
run
quit

Configuration

my.cnf configuration file

Galera needs also a my.cnf configuration file. Usually MySQL expects this file to be located at /etc/mysql/my.cnf. But the Percona packages don't ship any; on purpose: https://bugs.launchpad.net/percona-server/+bug/673844

Thus, you need to obtain / install / create one on your own. Make sure it has no settings which are forbidden for Galera. This includes the query_cache (it must not be enabled with Galera) and probably other settings which would contradict the settings explained in the next section.

Default location for my.cnf file based on different Linux Distros.

• If you are using Debian Linux file is located at /etc/mysql/my.cnf location
• If you are using Red Hat Linux/Centos Linux file is located at /etc/my.cnf location

Make sure you apply standard tunings for your memory size, number of allowed connections, and stuff.

We assume in the following that the my.cnf file has a directive like !includedir /etc/mysql/conf.d, such that you can put additional config files ending with .cnf there.

A sample my.cnf file serving as a starting point is provided here: My.cnf. Make sure you read the whole article and adjust that file to suit your needs before actually using it.

Caveat: we found out that Galera performs suboptimal when using innodb_flush_log_at_trx_commit=1. We leave up to you to assess whether this is a no-go for your environment or not. For Galera reasonable values for this parameter are innodb_flush_log_at_trx_commit=2 or ...=0. Make sure to read the documentataion of this parameter and that you understand its implication before using it.

Furthermore, you need to set the "datadir" configurable in the my.cnf file, even if you are on the default and do not want to change it. Some SST methods depend the setting being explicitly present in the configuration file.

wsrep.cnf configuration file

The Galera configuration then happens in a section called "wsrep", "write set replication", which is the internal name for the replication mechanism Galera is based on. A sample /etc/mysql/conf.d/wsrep.cnf file looks like:

[mysqld]
# the following lines are required for galera:
binlog_format=ROW
default-storage-engine=innodb
innodb_autoinc_lock_mode=2
innodb_locks_unsafe_for_binlog=1
query_cache_size=0
query_cache_type=0
bind-address=0.0.0.0
wsrep_provider=/usr/lib64/libgalera_smm.so
# NOTE: on Wheezy, use this path:
# wsrep_provider=/usr/lib/libgalera_smm.so
# the following lines need to be adjusted to your environment ... CHANGE THE PASSWORD! :-)
wsrep_cluster_name="my_wsrep_cluster"
wsrep_cluster_address="gcomm://<GALERA_NODE1_IP>,<GALERA_NODE2_IP>,<GALERA_NODE3_IP>"
wsrep_sst_method=xtrabackup
wsrep_sst_auth=wsrep:5ojijmedUg8
# It is recommended to run Galera in synchronous mode, which makes it possible
# to disable the OX builtin database replication monitor.
# Default is semi-synchronous mode. To enable synchronous mode, use
wsrep_causal_reads=1

When you adjusted those files, make sure they are identical on all nodes.

The replication user will be created later when the DB is running on the first node.

Cluster startup

Whenever not all nodes of a Galera cluster are running (like before starting the cluster for the very first time), the first Galera node needs to get started with the wsrep_cluster_address parameter overridden to the value "gcomm://" in order to denote that the node shall not try to join an existing cluster (which would inevitably fail now, because no other cluster nodes are running yet), but to bootstrap the cluster instead. This override can most conveniently done on the command line, instead of editing to wsrep.cnf file to and fro.

So, for the first node, the startup command is

mysqld_safe --wsrep_cluster_address=gcomm:// &

You should then verify the Galera module is loaded properly using

mysql -e "show status like 'wsrep%';"

You should verify some settings like

| wsrep_local_state_comment  | Synced                               |
| wsrep_cluster_size         | 1                                    |
| wsrep_cluster_status       | Primary                              |
| wsrep_connected            | ON                                   |
| wsrep_provider_name        | Galera                               |
| wsrep_provider_vendor      | Codership Oy <info@codership.com>    |
| wsrep_provider_version     | 2.8(r162)                            |
| wsrep_ready                | ON                                   |

Now you need to create the database user for the replication on this first node:

# create wsrep user: in mysql shell:
CREATE USER 'wsrep'@'localhost' IDENTIFIED BY '5ojijmedUg8';
GRANT RELOAD, LOCK TABLES, REPLICATION CLIENT ON *.* TO 'wsrep'@'localhost';
FLUSH PRIVILEGES;

The Galera peers can then be started on the nodes 2 and 3 using

mysqld_safe &

Since the standard service startup scripts cannot account for this special treatment, we recomment not to use them.

You can check the status of the Galera cluster using

mysql -e "show status like 'wsrep%';"

The output is lengthy. The most relevant fields are given as follows:

+----------------------------+----------------------------------------------------------------------+
| Variable_name              | Value                                                                |
+----------------------------+----------------------------------------------------------------------+
| wsrep_local_state_comment  | Synced                                                               |
| wsrep_incoming_addresses   | <GALERA_NODE1_IP>:3306,<GALERA_NODE2_IP>:3306,<GALERA_NODE3_IP>:3306 |
| wsrep_cluster_size         | 3                                                                    |
| wsrep_cluster_status       | Primary                                                              |
| wsrep_connected            | ON                                                                   |
| wsrep_ready                | ON                                                                   |
+----------------------------+----------------------------------------------------------------------+

Troubleshooting

The logs are helpful. Always.

Common mistakes are listed below.

If the Galera module does not get loaded at all:

• Configuration settings in my.cnf which are incompatible to Galera
• Wrong path of the shared object providing the Galera plugin in wsrep.cnf (wsrep_provider)

If the first node starts, but the second / third nodes can not be added to the cluster:

• User for the replication not created correctly on the first Galera node

Notes about configuring OX for use with Galera

Write requests

Open-Xchange supports Galera as database backend only in the configuration where all writes are directed to one Galera node. For availability, it makes sense to configure a floating IP as write IP for OX, which can be transferred from one Galera to another Galera node if needed. We recommend putting the control of such a floating IP under the control of some HA cluster software like pacemaker/corosync.

Read requests

You can chose between using a load balancer, using a floating IP for the read requests, or use the write requests floating IP.

• Load balancer based setup: Read requests get distributed aribtrarily between the Galera nodes. You require a load balancer for this. See next section. Then, in this configuration, you have two alternatives:
  • The Galera option wsrep_causal_reads=1 option enables you to configure OX with its replication monitor disabled (com.openexchange.database.replicationMonitor=false in configdb.properties).
  • Alternatively, you can run Galera with wsrep_causal_reads=0 when switching on OX builtin replication monitor. This setup however seems to be inferior from the performance point of view.
• Use a designated floating IP for the read requests: This eliminates the need of a load balancer. Since read requests do not seem to be performance-limiting, we expect to perform this option on par with the loadbalancer option.
• Use the floating IP for the writes also for the reads: In this scenario, you direct all database queries only to one Galera node, and the other two nodes are only getting queries in case of a failure of that node. In this case, you can even use wsrep_causal_reads=0 wile still having OX builtin replication monitor switched off.

Loadbalancer options

While the JDBC driver has some round-robin load balancing capabilities built-in, we don't recommend it for production use since it lacks possibilities to check the Galera nodes health states.

For most productions setup customers use enterprise-grade loadbalancing appliances. Those should get configured to check node availability not only on the TCP level, but to query the Galera sync status periodically. For an example of such an health check, see the our documentation for setting up a software loadbalancer using keepalived (next paragraph).

It is possible to use Keepalived to create a software loadbalancer on a therefore dedicated linux node. Documentation is available here. This implements the round-robin part for the read requests. For the single-node write behavior, we recommend to use a floating IP then.

In case where the Keepalived based approach is not feasible due to its requirements on the infrastructure, it is also possible to use a HAproxy based solution where HAproxy processes run on each of the OX nodes, configured for one round-robin and one active/passive instance. OX is then connecting to the local HAproxy instances. It is vital to configure HAproxy timeouts different from the defaults, otherwise HAproxy will kill active DB connections, causing errors. Some configuration hints for HAproxy are available here.

Master/Master database setup

This section describes the setup process "Master/Master replication" for new Open-Xchange database cluster. During configuration and initialization, other database operations must be prohibited.

The Master/Master replication is a vice versa setup of Master/Slave configurations. This means each server is afterwards the slave of the other.

Server IPs in the example are 1.1.1.1 and 9.9.9.9

Startup both database machines and install the mysql server packages

$ apt-get install mysql-server

During the installation, a dialog will show up to set a password for the MySQL 'root' user.

Open the MySQL configuration file on both servers:

$ vim /etc/mysql/my.cnf

Modify or enable the following configuration options in the mysqld-section, use 1 as ${unique Number} on the server 1.1.1.1 and 2 for 9.9.9.9:

bind-address            = 0.0.0.0
server-id               = ${unique Number}
log_bin                 = /var/log/mysql/mysql-bin.log
binlog_format           = statement
max_allowed_packet      = 16M

• bindaddress specifies the network address where MySQL is listening for network connections. Since the MySQL slave and both Open-Xchange Servers are dedicated machines it is required to have the master accessible through the network.
• server-id is just a unique number within a environment with multiple MySQL servers. It needs to be unique for each server in a replication cluster.
• log-bin enables the MySQL binary log which is required for Master/Master replication. In general every statement triggered at the database is stored there to get distributed through the database cluster.

To apply the configuration changes, restart the MySQL servers.

$ /etc/init.d/mysql restart

Then login to MySQL with the credentials given at the MySQL installation process

$ mysql -u root -p
Enter password:

First Master configuration

Choose one server to start with as the first Master (here we use 1.1.1.1).

Create a MySQL user with rights "REPLICATION". This account is used by the MySQL slave to fetch database updates. In this example, the username is "replication":

 mysql> GRANT REPLICATION SLAVE ON *.* TO 'replication'@'9.9.9.9' IDENTIFIED BY 'secret';

Verify that the MySQL daemon writes a binary log and note the log Position and File name:

mysql> SHOW MASTER STATUS;
+------------------+----------+--------------+------------------+
| File             | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+------------------+----------+--------------+------------------+
| mysql-bin.000001 |     1111 |              |                  |
+------------------+----------+--------------+------------------+

First Slave configuration

On 9.9.9.9, set the MySQL system user as owner of the binary log that has just been copied to the slave.

$ chown mysql:adm /var/log/mysql/*

Configure MySQL on 9.9.9.9 to use 1.1.1.1 as Master Server. (Use the actual log File name and Position which you just obtained with the command SHOW MASTER STATUS on 1.1.1.1. as explained above.)

mysql> CHANGE MASTER TO MASTER_HOST='1.1.1.1', MASTER_USER='replication', MASTER_PASSWORD='secret', MASTER_LOG_FILE='mysql-bin.000001', MASTER_LOG_POS=1111;

Start the MySQL slave replication

mysql> START SLAVE;

And check the status

mysql> SHOW SLAVE STATUS\G;

"Slave_IO_Running" and "Slave_SQL_Running" should be set to "yes". Furthermore "Read_Master_Log_Pos" should be counting and "Seconds_Behind_Master" should be approaching the 0 mark.

Second Master configuration

This means, the first Master/Slave Replication is working and the "reverse" replication needs to be prepared. Please now create the replication user on 9.9.9.9:

 mysql> GRANT REPLICATION SLAVE ON *.* TO 'replication'@'1.1.1.1' IDENTIFIED BY 'secret';

Verify that the MySQL daemon writes a binary log and remember the log Position:

mysql> SHOW MASTER STATUS;
+------------------+----------+--------------+------------------+
| File             | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+------------------+----------+--------------+------------------+
| mysql-bin.000009 |      9999|              |                  |
+------------------+----------+--------------+------------------+

Second Slave configuration

1.1.1.1 is now the slave in this context and 9.9.9.9 is the master. Log in to 1.1.1.1

Configure MySQL on 1.1.1.1 to use 9.9.9.9 as Master Server. Use the remembered log and file position from 1.1.1.1.

mysql> CHANGE MASTER TO MASTER_HOST='9.9.9.9', MASTER_USER='replication', MASTER_PASSWORD='secret', MASTER_LOG_FILE='mysql-bin.000009', MASTER_LOG_POS=9999;

start the MySQL slave replication

mysql> START SLAVE;

and check the status

mysql> SHOW SLAVE STATUS\G;

"Slave_IO_Running" and "Slave_SQL_Running" should be set to "yes". Furthermore "Read_Master_Log_Pos" should be counting and "Seconds_Behind_Master" should be approaching the 0 mark.

Also check the syslog if the replication has been sucessfully started

$ tail -fn20 /var/log/syslog
Jul 26 19:03:45 dbslave mysqld[4718]: 090726 19:03:45 [Note] Slave I/O thread: connected to master 'replication@1.1.1.17:3306',  replication started in log 'mysql-bin.000001' at position 10000

Testing Master/Master

On 1.1.1.1, create a new database in MySQL:

mysql> CREATE DATABASE foo;

Verify the database to als be available on 9.9.9.9 afterwards:

mysql> SHOW DATABASES;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| foo                |
| mysql              |
+--------------------+

Delete the new database on 9.9.9.9:

mysql> DROP DATABASE foo;

Check if the database has also been removed on 1.1.1.1

mysql> SHOW DATABASES;
+--------------------+
| Database           |
+--------------------+
| information_schema |
| mysql              |
+--------------------+

Creating Open-Xchange user

Now setup access for the Open-Xchange Server database user 'openexchange' to configdb and the oxdb for both groupware server addresses. These databases do not exist yet, but will be created during the Open-Xchange Server installation.

Note: The IPs in this example belong to the two different Open-Xchange Servers, please adjust them accordingly.

mysql> GRANT ALL PRIVILEGES ON *.* TO 'openexchange'@'10.20.30.213' IDENTIFIED BY 'secret';
mysql> GRANT ALL PRIVILEGES ON *.* TO 'openexchange'@'10.20.30.215' IDENTIFIED BY 'secret';