bsder and Kathryn Hancox
The author selected the Free and Open Source Fund to receive a donation as part of the Write for DOnations program.
Clustering adds high availability to your database by distributing changes to different servers. In the event that one of the instances fails, others are quickly available to continue serving.
Clusters come in two general configurations, active-passive and active-active. In active-passive clusters, all writes are done on a single active server and then copied to one or more passive servers that are poised to take over only in the event of an active server failure. Some active-passive clusters also allow SELECT
operations on passive nodes. In an active-active cluster, every node is read-write and a change made to one is replicated to all.
MariaDB is an open source relational database system that is fully compatible with the popular MySQL RDBMS system. You can read the official documentation for MariaDB at this page. Galera is a database clustering solution that enables you to set up multi-master clusters using synchronous replication. Galera automatically handles keeping the data on different nodes in sync while allowing you to send read and write queries to any of the nodes in the cluster. You can learn more about Galera at the official documentation page.
In this guide, you will configure an active-active MariaDB Galera cluster. For demonstration purposes, you will configure and test three Debian 9 Droplets that will act as nodes in the cluster. This is the smallest configurable cluster.
To follow along, you will need a DigitalOcean account, in addition to the following:
sudo
privileges.
sudo
privileges, follow our Initial Server Setup with Debian 9 tutorial.While the steps in this tutorial have been written for and tested against DigitalOcean Droplets, much of them should also be applicable to non-DigitalOcean servers with private networking enabled.
In this step, you will add the relevant MariaDB package repositories to each of your three servers so that you will be able to install the right version of MariaDB used in this tutorial. Once the repositories are updated on all three servers, you will be ready to install MariaDB.
One thing to note about MariaDB is that it originated as a drop-in replacement for MySQL, so in many configuration files and startup scripts, you’ll see mysql
rather than mariadb
. For consistency’s sake, we will use mysql
in this guide where either could work.
In this tutorial, you will use MariaDB version 10.4. Since this version isn’t included in the default Debian repositories, you’ll start by adding the external Debian repository maintained by the MariaDB project to all three of your servers.
To add the repository, you will first need to install the dirmngr
and software-properties-common
packages. dirmngr
is a server for managing repository certificates and keys. software-properties-common
is a package that allows easy addition and updates of source repository locations. Install the two packages by running:
- sudo apt install dirmngr software-properties-common
Note: MariaDB is a well-respected provider, but not all external repositories are reliable. Be sure to install only from trusted sources.
You’ll add the MariaDB repository key with the apt-key
command, which the APT package manager will use to verify that the package is authentic:
- sudo apt-key adv --recv-keys --keyserver hkp://keyserver.ubuntu.com:80 0xF1656F24C74CD1D8
Once you have the trusted key in the database, you can add the repository with the following command:
- sudo add-apt-repository 'deb [arch=amd64] http://nyc2.mirrors.digitalocean.com/mariadb/repo/10.4/debian stretch main'
After adding the repository, run apt update
in order to include package manifests from the new repository:
- sudo apt update
Once you have completed this step on your first server, repeat for your second and third servers.
Now that you have successfully added the package repository on all three of your servers, you’re ready to install MariaDB in the next section.
In this step, you will install the actual MariaDB packages on your three servers.
Beginning with version 10.1
, the MariaDB Server and MariaDB Galera Server packages are combined, so installing mariadb-server
will automatically install Galera and several dependencies:
- sudo apt install mariadb-server
You will be asked to confirm whether you would like to proceed with the installation. Enter yes
to continue with the installation.
From MariaDB version 10.4
onwards, the root MariaDB user does not have a password by default. To set a password for the root user, start by logging into MariaDB:
- sudo mysql -uroot
Once you’re inside the MariaDB shell, change the password by executing the following statement:
- set password = password("your_password");
You will see the following output indicating that the password was set correctly:
OutputQuery OK, 0 rows affected (0.001 sec)
Exit the MariaDB shell by running the following command:
- quit;
If you would like to learn more about SQL or need a quick refresher, check out our MySQL tutorial.
You now have all of the pieces necessary to begin configuring the cluster, but since you’ll be relying on rsync
in later steps, make sure it’s installed:
- sudo apt install rsync
This will confirm that the newest version of rsync
is already available or prompt you to upgrade or install it.
Once you have installed MariaDB and set the root password on your first server, repeat these steps for your other two servers.
Now that you have installed MariaDB successfully on each of the three servers, you can proceed to the configuration step in the next section.
In this step you will configure your first node. Each node in the cluster needs to have a nearly identical configuration. Because of this, you will do all of the configuration on your first machine, and then copy it to the other nodes.
By default, MariaDB is configured to check the /etc/mysql/conf.d
directory to get additional configuration settings from files ending in .cnf
. Create a file in this directory with all of your cluster-specific directives:
- sudo nano /etc/mysql/conf.d/galera.cnf
Add the following configuration into the file. The configuration specifies different cluster options, details about the current server and the other servers in the cluster, and replication-related settings. Note that the IP addresses in the configuration are the private addresses of your respective servers; replace the highlighted lines with the appropriate IP addresses.
[mysqld]
binlog_format=ROW
default-storage-engine=innodb
innodb_autoinc_lock_mode=2
bind-address=0.0.0.0
# Galera Provider Configuration
wsrep_on=ON
wsrep_provider=/usr/lib/galera/libgalera_smm.so
# Galera Cluster Configuration
wsrep_cluster_name="test_cluster"
wsrep_cluster_address="gcomm://First_Node_IP,Second_Node_IP,Third_Node_IP"
# Galera Synchronization Configuration
wsrep_sst_method=rsync
# Galera Node Configuration
wsrep_node_address="This_Node_IP"
wsrep_node_name="This_Node_Name"
mysqld
must not be bound to the IP address for localhost
. You can learn about the settings in more detail on the Galera Cluster system configuration page.wsrep_cluster_name
to something more meaningful than test_cluster
or leave it as-is, but you must update wsrep_cluster_address
with the private IP addresses of your three servers.rsync
, because it’s commonly available and does what you’ll need for now.wsrep_node_address
must match the address of the machine you’re on, but you can choose any name you want in order to help you identify the node in log files.When you are satisfied with your cluster configuration file, copy the contents into your clipboard, save and close the file. With the nano text editor, you can do this by pressing CTRL+X
, typing y
, and pressing ENTER
.
Now that you have configured your first node successfully, you can move on to configuring the remaining nodes in the next section.
In this step, you will configure the remaining two nodes. On your second node, open the configuration file:
- sudo nano /etc/mysql/conf.d/galera.cnf
Paste in the configuration you copied from the first node, then update the Galera Node Configuration
to use the IP address or resolvable domain name for the specific node you’re setting up. Finally, update its name, which you can set to whatever helps you identify the node in your log files:
. . .
# Galera Node Configuration
wsrep_node_address="This_Node_IP"
wsrep_node_name="This_Node_Name"
. . .
Save and exit the file.
Once you have completed these steps, repeat them on the third node.
You’re almost ready to bring up the cluster, but before you do, make sure that the appropriate ports are open in your firewall.
In this step, you will configure your firewall so that the ports required for inter-node communication are open. On every server, check the status of the firewall by running:
- sudo ufw status
In this case, only SSH is allowed through:
OutputStatus: active
To Action From
-- ------ ----
OpenSSH ALLOW Anywhere
OpenSSH (v6) ALLOW Anywhere (v6)
Since only SSH traffic is permitted in this case, you’ll need to add rules for MySQL and Galera traffic. If you tried to start the cluster, it would fail because of firewall rules.
Galera can make use of four ports:
3306
For MySQL client connections and State Snapshot Transfer that use the mysqldump
method.4567
For Galera Cluster replication traffic. Multicast replication uses both UDP transport and TCP on this port.4568
For Incremental State Transfer.4444
For all other State Snapshot Transfer.In this example, you’ll open all four ports while you do your setup. Once you’ve confirmed that replication is working, you’d want to close any ports you’re not actually using and restrict traffic to just servers in the cluster.
Open the ports with the following command:
- sudo ufw allow 3306,4567,4568,4444/tcp
- sudo ufw allow 4567/udp
Note: Depending on what else is running on your servers you might want to restrict access right away. The UFW Essentials: Common Firewall Rules and Commands guide can help with this.
After you have configured your firewall on the first node, create the same firewall settings on the second and third node.
Now that you have configured the firewalls successfully, you’re ready to start the cluster in the next step.
In this step, you will start your MariaDB cluster. To begin, you need to stop the running MariaDB service so that you can bring your cluster online.
Use the following command on all three servers to stop MariaDB so that you can bring them back up in a cluster:
- sudo systemctl stop mysql
systemctl
doesn’t display the outcome of all service management commands, so to be sure you succeeded, use the following command:
- sudo systemctl status mysql
If the last line looks something like the following, the command was successful:
Output. . .
Apr 26 03:34:23 galera-node-01 systemd[1]: Stopped MariaDB 10.4.4 database server.
Once you’ve shut down mysql
on all of the servers, you’re ready to proceed.
To bring up the first node, you’ll need to use a special startup script. The way you’ve configured your cluster, each node that comes online tries to connect to at least one other node specified in its galera.cnf
file to get its initial state. Without using the galera_new_cluster
script that allows systemd to pass the --wsrep-new-cluster
parameter, a normal systemctl start mysql
would fail because there are no nodes running for the first node to connect with.
- sudo galera_new_cluster
This command will not display any output on successful execution. When this script succeeds, the node is registered as part of the cluster, and you can see it with the following command:
- mysql -u root -p -e "SHOW STATUS LIKE 'wsrep_cluster_size'"
You will see the following output indicating that there is one node in the cluster:
Output+--------------------+-------+
| Variable_name | Value |
+--------------------+-------+
| wsrep_cluster_size | 1 |
+--------------------+-------+
On the remaining nodes, you can start mysql
normally. They will search for any member of the cluster list that is online, so when they find one, they will join the cluster.
Now you can bring up the second node. Start mysql
:
- sudo systemctl start mysql
No output will be displayed on successful execution. You will see your cluster size increase as each node comes online:
- mysql -u root -p -e "SHOW STATUS LIKE 'wsrep_cluster_size'"
You will see the following output indicating that the second node has joined the cluster and that there are two nodes in total.
Output+--------------------+-------+
| Variable_name | Value |
+--------------------+-------+
| wsrep_cluster_size | 2 |
+--------------------+-------+
It’s now time to bring up the third node. Start mysql
:
- sudo systemctl start mysql
Run the following command to find the cluster size:
- mysql -u root -p -e "SHOW STATUS LIKE 'wsrep_cluster_size'"
You will see the following output, which indicates that the third node has joined the cluster and that the total number nodes in the cluster is three.
Output+--------------------+-------+
| Variable_name | Value |
+--------------------+-------+
| wsrep_cluster_size | 3 |
+--------------------+-------+
At this point, the entire cluster is online and communicating successfully. Next, you can ensure the working setup by testing replication in the next section.
You’ve gone through the steps up to this point so that your cluster can perform replication from any node to any other node, known as active-active replication. Follow the steps below to test and see if the replication is working as expected.
You’ll start by making database changes on your first node. The following commands will create a database called playground
and a table inside of this database called equipment
.
- mysql -u root -p -e 'CREATE DATABASE playground;
- CREATE TABLE playground.equipment ( id INT NOT NULL AUTO_INCREMENT, type VARCHAR(50), quant INT, color VARCHAR(25), PRIMARY KEY(id));
- INSERT INTO playground.equipment (type, quant, color) VALUES ("slide", 2, "blue");'
In the previous command, the CREATE DATABASE
statement creates a database named playground
. The CREATE
statement creates a table named equipment
inside the playground
database having an auto-incrementing identifier column called id
and other columns. The type
column, quant
column, and color
column are defined to store the type, quantity, and color of the equipment respectively. The INSERT
statement inserts an entry of type slide
, quantity 2
, and color blue
.
You now have one value in your table.
Next, look at the second node to verify that replication is working:
- mysql -u root -p -e 'SELECT * FROM playground.equipment;'
If replication is working, the data you entered on the first node will be visible here on the second:
Output+----+-------+-------+-------+
| id | type | quant | color |
+----+-------+-------+-------+
| 1 | slide | 2 | blue |
+----+-------+-------+-------+
From this same node, you can write data to the cluster:
- mysql -u root -p -e 'INSERT INTO playground.equipment (type, quant, color) VALUES ("swing", 10, "yellow");'
From the third node, you can read all of this data by querying the table again:
- mysql -u root -p -e 'SELECT * FROM playground.equipment;'
You will see the following output showing the two rows:
Output +----+-------+-------+--------+
| id | type | quant | color |
+----+-------+-------+--------+
| 1 | slide | 2 | blue |
| 2 | swing | 10 | yellow |
+----+-------+-------+--------+
Again, you can add another value from this node:
- mysql -u root -p -e 'INSERT INTO playground.equipment (type, quant, color) VALUES ("seesaw", 3, "green");'
Back on the first node, you can verify that your data is available everywhere:
- mysql -u root -p -e 'SELECT * FROM playground.equipment;'
You will see the following output that indicates the rows are available on the first node.
Output +----+--------+-------+--------+
| id | type | quant | color |
+----+--------+-------+--------+
| 1 | slide | 2 | blue |
| 2 | swing | 10 | yellow |
| 3 | seesaw | 3 | green |
+----+--------+-------+--------+
You’ve successfully verified that you can write to all of the nodes and that replication is being performed properly.
At this point, you have a working three-node Galera test cluster configured. If you plan on using a Galera cluster in a production situation, it’s recommended that you begin with no fewer than five nodes.
Before production use, you may want to take a look at some of the other state snapshot transfer (sst) agents like xtrabackup, which allows you to set up new nodes very quickly and without large interruptions to your active nodes. This does not affect the actual replication, but is a concern when nodes are being initialized.
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