How To Create a Multi-Node MySQL Cluster on Ubuntu 18.04

Introduction

The MySQL Cluster distributed database provides high availability and throughput for your MySQL database management system. A MySQL Cluster consists of one or more management nodes (ndb_mgmd) that store the cluster’s configuration and control the data nodes (ndbd), where cluster data is stored. After communicating with the management node, clients (MySQL clients, servers, or native APIs) connect directly to these data nodes.

With MySQL Cluster there is typically no replication of data, but instead data node synchronization. For this purpose a special data engine must be used — NDBCluster (NDB). It’s helpful to think of the cluster as a single logical MySQL environment with redundant components. Thus, a MySQL Cluster can participate in replication with other MySQL Clusters.

MySQL Cluster works best in a shared-nothing environment. Ideally, no two components should share the same hardware. For simplicity and demonstration purposes, we’ll limit ourselves to using only three servers. We will set up two servers as data nodes which sync data between themselves. The third server will be used for the Cluster Manager and also for the MySQL server/client. If you spin up additional servers, you can add more data nodes to the cluster, decouple the cluster manager from the MySQL server/client, and configure more servers as Cluster Managers and MySQL servers/clients.

Prerequisites

To complete this tutorial, you will need a total of three servers: two servers for the redundant MySQL data nodes (ndbd), and one server for the Cluster Manager (ndb_mgmd) and MySQL server/client (mysqld and mysql).

In the same DigitalOcean data center, create the following Droplets with private networking enabled:

• Three Ubuntu 18.04 Droplets with private networking enabled
• A non-root user with sudo privileges configured for each Droplet. You can learn how to do this in Initial Server Setup with Ubuntu 18.04.

Be sure to note down the private IP addresses of your three Droplets. In this tutorial our cluster nodes have the following private IP addresses:

• 198.51.100.0 will be the first MySQL Cluster data node
• 198.51.100.1 will be the second data node
• 198.51.100.2 will be the Cluster Manager & MySQL server node

Once you’ve spun up your Droplets, configured a non-root user, and noted down the IP addresses for the 3 nodes, you’re ready to begin with this tutorial.

Step 1 — Installing and Configuring the Cluster Manager

We’ll first begin by downloading and installing the MySQL Cluster Manager, ndb_mgmd.

To install the Cluster Manager, we first need to fetch the appropriate .deb installer file from the the official MySQL Cluster download page.

From this page, under Select Operating System, choose Ubuntu Linux. Then, under Select OS Version, choose Ubuntu Linux 18.04 (x86, 64-bit).

Scroll down until you see DEB Package, NDB Management Server, and click on the Download link for the one that does not contain dbgsym (unless you require debug symbols). You will be brought to a Begin Your Download page. Here, right click on No thanks, just start my download. and copy the link to the .deb file.

Now, log in to your Cluster Manager Droplet (in this tutorial, 198.51.100.2), and download this .deb file:

cd ~
wget https://dev.mysql.com/get/Downloads/MySQL-Cluster-7.6/mysql-cluster-community-management-server_7.6.6-1ubuntu18.04_amd64.deb

Install ndb_mgmd using dpkg:

sudo dpkg -i mysql-cluster-community-management-server_7.6.6-1ubuntu18.04_amd64.deb

We now need to configure ndb_mgmd before first running it; proper configuration will ensure correct synchronization and load distribution among the data nodes.

The Cluster Manager should be the first component launched in any MySQL cluster. It requires a configuration file, passed in as an argument to its executable. We’ll create and use the following configuration file: /var/lib/mysql-cluster/config.ini.

On the Cluster Manager Droplet, create the /var/lib/mysql-cluster directory where this file will reside:

sudo mkdir /var/lib/mysql-cluster

Then create and edit the configuration file using your preferred text editor:

sudo nano /var/lib/mysql-cluster/config.ini

Paste the following text into your editor:

[ndbd default]
# Options affecting ndbd processes on all data nodes:
NoOfReplicas=2	# Number of replicas

[ndb_mgmd]
# Management process options:
hostname=198.51.100.2 # Hostname of the manager
datadir=/var/lib/mysql-cluster 	# Directory for the log files

[ndbd]
hostname=198.51.100.0 # Hostname/IP of the first data node
NodeId=2			# Node ID for this data node
datadir=/usr/local/mysql/data	# Remote directory for the data files

[ndbd]
hostname=198.51.100.1 # Hostname/IP of the second data node
NodeId=3			# Node ID for this data node
datadir=/usr/local/mysql/data	# Remote directory for the data files

[mysqld]
# SQL node options:
hostname=198.51.100.2 # In our case the MySQL server/client is on the same Droplet as the cluster manager

After pasting in this text, being sure to replace the hostname values above with the correct IP addresses of the Droplets you’ve configured. Setting this hostname parameter is an important security measure that prevents other servers from connecting to the Cluster Manager.

Save the file and close your text editor.

This is a pared-down, minimal configuration file for a MySQL Cluster. You should customize the parameters in this file depending on your production needs. For a sample, fully configured ndb_mgmd configuration file, consult the MySQL Cluster documentation.

In the above file you can add additional components like data nodes (ndbd) or MySQL server nodes (mysqld) by appending instances to the appropriate section.

We can now start the manager by executing the ndb_mgmd binary and specifying its config file using the -f flag:

sudo ndb_mgmd -f /var/lib/mysql-cluster/config.ini

You should see the following output:

Output
MySQL Cluster Management Server mysql-5.7.22 ndb-7.6.6
2018-07-25 21:48:39 [MgmtSrvr] INFO     -- The default config directory '/usr/mysql-cluster' does not exist. Trying to create it...
2018-07-25 21:48:39 [MgmtSrvr] INFO     -- Successfully created config directory

This indicates that the MySQL Cluster Management server has successfully been installed and is now running on your Droplet.

Ideally, we’d like to start the Cluster Management server automatically on boot. To do this, we’re going to create and enable a systemd service.

Before we create the service, we need to kill the running server:

sudo pkill -f ndb_mgmd

Now, open and edit the following systemd Unit file using your favorite editor:

sudo nano /etc/systemd/system/ndb_mgmd.service

Paste in the following code:

[Unit]
Description=MySQL NDB Cluster Management Server
After=network.target auditd.service

[Service]
Type=forking
ExecStart=/usr/sbin/ndb_mgmd -f /var/lib/mysql-cluster/config.ini
ExecReload=/bin/kill -HUP $MAINPID
KillMode=process
Restart=on-failure

[Install]
WantedBy=multi-user.target

Here, we’ve added a minimal set of options instructing systemd on how to start, stop and restart the ndb_mgmd process. To learn more about the options used in this unit configuration, consult the systemd manual.

Save and close the file.

Now, reload systemd’s manager configuration using daemon-reload:

sudo systemctl daemon-reload

We’ll enable the service we just created so that the MySQL Cluster Manager starts on reboot:

sudo systemctl enable ndb_mgmd

Finally, we’ll start the service:

sudo systemctl start ndb_mgmd

You can verify that the NDB Cluster Management service is running:

sudo systemctl status ndb_mgmd

You should see the following output:

● ndb_mgmd.service - MySQL NDB Cluster Management Server
   Loaded: loaded (/etc/systemd/system/ndb_mgmd.service; enabled; vendor preset: enabled)
   Active: active (running) since Thu 2018-07-26 21:23:37 UTC; 3s ago
  Process: 11184 ExecStart=/usr/sbin/ndb_mgmd -f /var/lib/mysql-cluster/config.ini (code=exited, status=0/SUCCESS)
 Main PID: 11193 (ndb_mgmd)
    Tasks: 11 (limit: 4915)
   CGroup: /system.slice/ndb_mgmd.service
           └─11193 /usr/sbin/ndb_mgmd -f /var/lib/mysql-cluster/config.ini

Which indicates that the ndb_mgmd MySQL Cluster Management server is now running as a systemd service.

The final step for setting up the Cluster Manager is to allow incoming connections from other MySQL Cluster nodes on our private network.

If you did not configure the ufw firewall when setting up this Droplet, you can skip ahead to the next section.

We’ll add rules to allow local incoming connections from both data nodes:

sudo ufw allow from 198.51.100.0
sudo ufw allow from 198.51.100.1

After entering these commands, you should see the following output:

Output
Rule added

The Cluster Manager should now be up and running, and able to communicate with other Cluster nodes over the private network.

Step 2 — Installing and Configuring the Data Nodes

In this step, we’ll install the ndbd MySQL Cluster data node daemon, and configure the nodes so they can communicate with the Cluster Manager.

To install the data node binaries we first need to fetch the appropriate .deb installer file from the official MySQL download page.

From this page, under Select Operating System, choose Ubuntu Linux. Then, under Select OS Version, choose Ubuntu Linux 18.04 (x86, 64-bit).

Scroll down until you see DEB Package, NDB Data Node Binaries, and click on the Download link for the one that does not contain dbgsym (unless you require debug symbols). You will be brought to a Begin Your Download page. Here, right click on No thanks, just start my download. and copy the link to the .deb file.

Now, log in to your first data node Droplet (in this tutorial, 198.51.100.0), and download this .deb file:

cd ~
wget https://dev.mysql.com/get/Downloads/MySQL-Cluster-7.6/mysql-cluster-community-data-node_7.6.6-1ubuntu18.04_amd64.deb

Before we install the data node binary, we need to install a dependency, libclass-methodmaker-perl:

sudo apt update
sudo apt install libclass-methodmaker-perl

We can now install the data note binary using dpkg:

sudo dpkg -i mysql-cluster-community-data-node_7.6.6-1ubuntu18.04_amd64.deb

The data nodes pull their configuration from MySQL’s standard location, /etc/my.cnf. Create this file using your favorite text editor and begin editing it:

sudo nano /etc/my.cnf

Add the following configuration parameter to the file:

[mysql_cluster]
# Options for NDB Cluster processes:
ndb-connectstring=198.51.100.2  # location of cluster manager

Specifying the location of the Cluster Manager node is the only configuration needed for ndbd to start. The rest of the configuration will be pulled from the manager directly.

Save and exit the file.

In our example, the data node will find out that its data directory is /usr/local/mysql/data, per the manager’s configuration. Before starting the daemon, we’ll create this directory on the node:

sudo mkdir -p /usr/local/mysql/data

Now we can start the data node using the following command:

sudo ndbd

You should see the following output:

Output
2018-07-18 19:48:21 [ndbd] INFO     -- Angel connected to '198.51.100.2:1186'
2018-07-18 19:48:21 [ndbd] INFO     -- Angel allocated nodeid: 2

The NDB data node daemon has been successfully installed and is now running on your server.

We also need to allow incoming connections from other MySQL Cluster nodes over the private network.

If you did not configure the ufw firewall when setting up this Droplet, you can skip ahead to setting up the systemd service for ndbd.

We’ll add rules to allow incoming connections from the Cluster Manager and other data nodes:

sudo ufw allow from 198.51.100.0
sudo ufw allow from 198.51.100.2

After entering these commands, you should see the following output:

Output
Rule added

Your MySQL data node Droplet can now communicate with both the Cluster Manager and other data node over the private network.

Finally, we’d also like the data node daemon to start up automatically when the server boots. We’ll follow the same procedure used for the Cluster Manager, and create a systemd service.

Before we create the service, we’ll kill the running ndbd process:

sudo pkill -f ndbd

Now, open and edit the following systemd Unit file using your favorite editor:

sudo nano /etc/systemd/system/ndbd.service

Paste in the following code:

[Unit]
Description=MySQL NDB Data Node Daemon
After=network.target auditd.service

[Service]
Type=forking
ExecStart=/usr/sbin/ndbd
ExecReload=/bin/kill -HUP $MAINPID
KillMode=process
Restart=on-failure

[Install]
WantedBy=multi-user.target

Here, we’ve added a minimal set of options instructing systemd on how to start, stop and restart the ndbd process. To learn more about the options used in this unit configuration, consult the systemd manual.

Save and close the file.

Now, reload systemd’s manager configuration using daemon-reload:

sudo systemctl daemon-reload

We’ll now enable the service we just created so that the data node daemon starts on reboot:

sudo systemctl enable ndbd

Finally, we’ll start the service:

sudo systemctl start ndbd

You can verify that the NDB Cluster Management service is running:

sudo systemctl status ndbd

You should see the following output:

Output
● ndbd.service - MySQL NDB Data Node Daemon
   Loaded: loaded (/etc/systemd/system/ndbd.service; enabled; vendor preset: enabled)
   Active: active (running) since Thu 2018-07-26 20:56:29 UTC; 8s ago
  Process: 11972 ExecStart=/usr/sbin/ndbd (code=exited, status=0/SUCCESS)
 Main PID: 11984 (ndbd)
    Tasks: 46 (limit: 4915)
   CGroup: /system.slice/ndbd.service
           ├─11984 /usr/sbin/ndbd
           └─11987 /usr/sbin/ndbd

Which indicates that the ndbd MySQL Cluster data node daemon is now running as a systemd service. Your data node should now be fully functional and able to connect to the MySQL Cluster Manager.

Once you’ve finished setting up the first data node, repeat the steps in this section on the other data node (198.51.100.1 in this tutorial).

Step 3 — Configuring and Starting the MySQL Server and Client

A standard MySQL server, such as the one available in Ubuntu’s APT repository, does not support the MySQL Cluster engine NDB. This means we need to install the custom SQL server packaged with the other MySQL Cluster software we’ve installed in this tutorial.

We’ll once again grab the MySQL Cluster Server binary from the official MySQL Cluster download page.

From this page, under Select Operating System, choose Ubuntu Linux. Then, under Select OS Version, choose Ubuntu Linux 18.04 (x86, 64-bit).

Scroll down until you see DEB Bundle, and click on the Download link (it should be the first one in the list). You will be brought to a Begin Your Download page. Here, right click on No thanks, just start my download. and copy the link to the .tar archive.

Now, log in to the Cluster Manager Droplet (in this tutorial, 198.51.100.2), and download this .tar archive (recall that we are installing MySQL Server on the same node as our Cluster Manager – in a production setting you should run these daemons on different nodes):

cd ~
wget https://dev.mysql.com/get/Downloads/MySQL-Cluster-7.6/mysql-cluster_7.6.6-1ubuntu18.04_amd64.deb-bundle.tar

We’ll now extract this archive into a directory called install. First, create the directory:

mkdir install

Now extract the archive into this directory:

tar -xvf mysql-cluster_7.6.6-1ubuntu18.04_amd64.deb-bundle.tar -C install/

Move into this directory, containing the extracted MySQL Cluster component binaries:

cd install

Before we install the MySQL server binary, we need to install a couple of dependencies:

sudo apt update
sudo apt install libaio1 libmecab2

Now, we need to install the MySQL Cluster dependencies, bundled in the tar archive we just extracted :

sudo dpkg -i mysql-common_7.6.6-1ubuntu18.04_amd64.deb
sudo dpkg -i mysql-cluster-community-client_7.6.6-1ubuntu18.04_amd64.deb
sudo dpkg -i mysql-client_7.6.6-1ubuntu18.04_amd64.deb
sudo dpkg -i mysql-cluster-community-server_7.6.6-1ubuntu18.04_amd64.deb

When installing mysql-cluster-community-server, a configuration prompt should appear, asking you to set a password for the root account of your MySQL database. Choose a strong, secure password, and hit <Ok>. Re-enter this root password when prompted, and hit <Ok> once again to complete installation.

We can now install the MySQL server binary using dpkg:

sudo dpkg -i mysql-server_7.6.6-1ubuntu18.04_amd64.deb

We now need to configure this MySQL server installation.

The configuration for MySQL Server is stored in the default /etc/mysql/my.cnf file.

Open this configuration file using your favorite editor:

sudo nano /etc/mysql/my.cnf

You should see the following text:

# Copyright (c) 2015, 2016, Oracle and/or its affiliates. All rights reserved.
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; version 2 of the License.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA

#
# The MySQL Cluster Community Server configuration file.
#
# For explanations see
# http://dev.mysql.com/doc/mysql/en/server-system-variables.html

# * IMPORTANT: Additional settings that can override those from this file!
#   The files must end with '.cnf', otherwise they'll be ignored.
#
!includedir /etc/mysql/conf.d/
!includedir /etc/mysql/mysql.conf.d/

Append the following configuration to it:

. . .
[mysqld]
# Options for mysqld process:
ndbcluster                      # run NDB storage engine

[mysql_cluster]
# Options for NDB Cluster processes:
ndb-connectstring=198.51.100.2  # location of management server

Save and exit the file.

Restart the MySQL server for these changes to take effect:

sudo systemctl restart mysql

MySQL by default should start automatically when your server reboots. If it doesn’t, the following command should fix this:

sudo systemctl enable mysql

A SQL server should now be running on your Cluster Manager / MySQL Server Droplet.

In the next step, we’ll run a few commands to verify that our MySQL Cluster installation is functioning as expected.

Step 4 — Verifying MySQL Cluster Installation

To verify your MySQL Cluster installation, log in to your Cluster Manager / SQL Server node.

We’ll open the MySQL client from the command line and connect to the root account we just configured by entering the following command:

mysql -u root -p 

Enter your password when prompted, and hit ENTER.

You should see an output similar to:

Output
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.7.22-ndb-7.6.6 MySQL Cluster Community Server (GPL)

Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql>

Once inside the MySQL client, run the following command:

SHOW ENGINE NDB STATUS \G

You should now see information about the NDB cluster engine, beginning with connection parameters:

Output
*************************** 1. row ***************************
  Type: ndbcluster
  Name: connection
Status: cluster_node_id=4, connected_host=198.51.100.2, connected_port=1186, number_of_data_nodes=2, number_of_ready_data_nodes=2, connect_count=0
. . .

This indicates that you’ve successfully connected to your MySQL Cluster.

Notice here the number of ready_data_nodes: 2. This redundancy allows your MySQL cluster to continue operating even if one of the data nodes fails. It also means that your SQL queries will be load balanced across the two data nodes.

You can try shutting down one of the data nodes to test cluster stability. The simplest test would be to restart the data node Droplet in order to fully test the recovery process. You should see the value of number_of_ready_data_nodes change to 1 and back up to 2 again as the node reboots and reconnects to the Cluster Manager.

To exit the MySQL prompt, simply type quit or press CTRL-D.

This is the first test that indicates that the MySQL cluster, server, and client are working. We’ll now go through an additional test to confirm that the cluster is functioning properly.

Open the Cluster management console, ndb_mgm using the command:

ndb_mgm

You should see the following output:

Output
-- NDB Cluster -- Management Client --
ndb_mgm>

Once inside the console enter the command SHOW and hit ENTER:

SHOW

You should see the following output:

Output
Connected to Management Server at: 198.51.100.2:1186
Cluster Configuration
---------------------
[ndbd(NDB)]	2 node(s)
id=2	@198.51.100.0  (mysql-5.7.22 ndb-7.6.6, Nodegroup: 0, *)
id=3	@198.51.100.1  (mysql-5.7.22 ndb-7.6.6, Nodegroup: 0)

[ndb_mgmd(MGM)]	1 node(s)
id=1	@198.51.100.2  (mysql-5.7.22 ndb-7.6.6)

[mysqld(API)]	1 node(s)
id=4	@198.51.100.2  (mysql-5.7.22 ndb-7.6.6)

The above shows that there are two data nodes connected with node-ids 2 and 3. There is also one management node with node-id 1 and one MySQL server with node-id 4. You can display more information about each id by typing its number with the command STATUS as follows:

2 STATUS
``` 

The above command shows you the status, MySQL version, and NDB version of node 2:

```
[secondary_label Output]
Node 2: started (mysql-5.7.22 ndb-7.6.6)
```

To exit the management console type `quit`, and then hit `ENTER`.

The management console is very powerful and gives you many other options for administering the cluster and its data, including creating an online backup. For more information consult the [official MySQL documentation](https://dev.mysql.com/doc/refman/5.7/en/mysql-cluster-management.html).

At this point, you’ve fully tested your MySQL Cluster installation. The concluding step of this guide shows you how to create and insert test data into this MySQL Cluster.

## Step 5 — Inserting Data into MySQL Cluster

To demonstrate the cluster’s functionality, let's create a new table using the NDB engine and insert some sample data into it. Note that in order to use cluster functionality, the engine must be specified explicitly as **NDB**. If you use InnoDB (default) or any other engine, you will not make use of the cluster.

First, let's create a database called `clustertest` with the command:

```custom_prefix(mysql>)
CREATE DATABASE clustertest;
```

Next, switch to the new database:

```custom_prefix(mysql>)
USE clustertest;
```

Now, create a simple table called `test_table` like this:

```custom_prefix(mysql>)
CREATE TABLE test_table (name VARCHAR(20), value VARCHAR(20)) ENGINE=ndbcluster;
```

We have explicitly specified the engine `ndbcluster` in order to make use of the cluster. 

Now, we can start inserting data using this SQL query:

```custom_prefix(mysql>)
INSERT INTO test_table (name,value) VALUES('some_name','some_value');
```

To verify that the data has been inserted, run the following select query:

```custom_prefix(mysql>)
SELECT * FROM test_table;
```

When you insert data into and select data from an `ndbcluster` table, the cluster load balances queries between all the available data nodes. This improves the stability and performance of your MySQL database installation.

You can also set the default storage engine to `ndbcluster` in the `my.cnf` file that we edited previously. If you do this, you won’t need to specify the `ENGINE` option when creating tables. To learn more, consult the MySQL [Reference Manual](https://dev.mysql.com/doc/refman/5.7/en/storage-engine-setting.html).

## Conclusion

In this tutorial, we’ve demonstrated how to set up and configure a MySQL Cluster on Ubuntu 18.04 servers. It’s important to note that this is a minimal, pared-down architecture used to demonstrate the installation procedure, and there are many advanced options and features worth learning about before deploying MySQL Cluster in production (for example, performing backups). To learn more, consult the official [MySQL Cluster  documentation](https://dev.mysql.com/doc/refman/5.7/en/mysql-cluster.html).

If you use InnoDB (default) or any other engine, you will not make use of the cluster.