September 29, 2014 · mysql virtual machines high availability

Highly Available and Scalable Master-Master MySQL on Azure Virtual Machines

Introduction

Achieving High Availability on your database level is essential in order to maintain your application availability. On Azure, you can provision a managed highly-available MySQL database cluster through a 3rd party ClearDB.

In this post, I'm going to explore creating a highly available and scalable MySQL environment using Master-Master replication and the Azure Load Balancer.

Setting up Master-Master replication

MySQL replication is the process by which data stored in a MySQL database, is continuously copied to a second server, called "Master-Slave" replication. On the other hand, what we will be exploring here is "Master-Master" replication, where data is bi-directionally copied between two servers. This allows us to perform reads or writes from either server, ensuring high availability and scalability.

Step 1 - Setting up the infrastructure

Login to the new Azure Portal and click on New, then choose Ubuntu 14.04 LTS to start.
Creating the VM

Now fill in the data require. In my setup I've used mysql1 as the hostname of this first machine, and I've customized the Cloud Service name to be mysqlha.

Additionally, you'll need to provide an SSH key for logging in to the machines with certificates, so here is how to generate an SSH key for Azure if you haven't already.

Configuration of the VM

Additionally, we will need to manually assign a static IP address (instead of relying on DHCP) to ensure that even if we stop or restart a machine, it will come up with the same address.

Assign static IP address

Once the machine has been created, we need to add it to an Availability Set

Configure Availability Set

Now, let's add a second Virtual Machine to the same Cloud Service and availablity set by going to the Resource Group, and adding a new resource (Virtual Machine), specifying the hostname to be mysql2 and the same user name and SSH key.

Adding another VM to the Resource Group

What is important to notice is, when creating this second Virtual Machine, you have to add it to the same Availability Set of the first mysql1 machine. You might also want to use the same Storage Account.

Make sure you configure a different Static IP.

Create the VM in the same Availablility Set

Now let the portal create the second Virtual Machine.

Step 2 - Installing MySQL

Once both machines are up and running, we'll need to SSH into each machine and run a few commands to install MySQL and setup the replication.

The SSH endpoint on both machines would be your Cloud Service name, in my case here that would be mysqlha.cloudapp.net and the port would be the one defined in the Endpoints. For mysql1 that would be port 22, for mysql2 that would be 50793 which was randomly assigned by the portal.

Finding out the SSH endpoint

Using your favorite SSH client, SSH into your machines one by one to setup.

Virtual Machine: mysql1

Install MySQL

Once you're connected, update the package sources
sudo apt-get update

Then let's install mysql-server and mysql-client packages
sudo apt-get install mysql-server mysql-client

Create replication user

Create the replication user and specify a password
create user 'replicator'@'%' identified by 'aComplexPassword';

Then give him permissions to replicate all databases (that are specified in the config file)
grant replication slave, replication client on *.* to 'replicator'@'%';

Then run flush privileges; to apply changes to the user table.

After this step is completed, you should be able to login to mysql1 from mysql2 through the replicator user.

Configure replication

We need to edit and set some parameters in MySQL configuration to ensure correct replication. Open the config file using your favorite editor bysudo nano /etc/mysql/my.cnf

relay-log = /var/log/mysql/relay-bin
relay-log-index = /var/log/mysql/relay-bin.index
relay-log-info-file = /var/log/mysql/relay-bin.info
auto_increment_increment = 2
auto_increment_offset    = 1

To summarize, here are the final list of changes and variables under [mysqld]:

#bind-address = 127.0.0.1
server-id = 1
log_bin = /var/log/mysql/mysql-bin.log
binlog_do_db = exampledb # your database name here
relay-log = /var/log/mysql/relay-bin
relay-log-index = /var/log/mysql/relay-bin.index
relay-log-info-file = /var/log/mysql/relay-bin.info
auto_increment_increment = 2
auto_increment_offset    = 1
log_slave_updates         = 1

Ctrl-X then Y to save and exit.

Restart mysql sudo service mysql restart

Finally, we need 2 pieces of information to setup the replication on the slave mysql2, we can obtain them through show master status; which will output something similar to:

+------------------+----------+--------------+------------------+
| File             | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+------------------+----------+--------------+------------------+
| mysql-bin.000001 |      343 | exampledb    |                  |
+------------------+----------+--------------+------------------+
1 row in set (0.00 sec)

The information we need is the File and Position. Make note of them, they are probably different on your server than from what you see here.

Virtual Machine: mysql2

For our second MySQL node, mysql2, we'll configure it using the exact same steps as we've did for mysql1 (install MySQL, add replication user and configure) with the exception to setting the server-id = 2 and auto_increment_offset = 2 in the /etc/mysql/my.cnf config file.

Step 3 - Setup replication between mysql1 and mysql2

Create the database on mysql1

On mysql1, in a MySQL prompt, create the exampledb
create database exampledb;

Point the slave mysql2 to master mysql1

On mysql2, in this step, we will need:

Then run the below on the MySQL prompt replacing the values with your values:

slave stop;
CHANGE MASTER TO MASTER_HOST = 'mysql1', MASTER_USER = 'replicator', MASTER_PASSWORD = 'aComplexPassword', MASTER_LOG_FILE = 'mysql-bin.000001',  MASTER_LOG_POS = 344;

Start replication

After doing the above, start the slave on mysql2 then show the status of the replication relationship

slave start;
show slave status;

Test mysql1 to mysql2 replication

On mysql1, create a new table on the exampledb
create table exampledb.dummy(id INT NOT NULL AUTO_INCREMENT PRIMARY KEY, data varchar(100)); then insert a couple of rows

insert into exampledb.dummy SET data='mysql 1 to 2 replication test';
insert into exampledb.dummy SET data='mysql 1 to 2 replication test another row';

Once you do that and do a select * from exampledb.dummy on mysql2 you should find the rows nicely waiting for you:

mysql> select * from exampledb.dummy;
+----+-------------------------------------------+
| id | data                                      |
+----+-------------------------------------------+
|  1 | mysql 1 to 2 replication test             |
|  3 | mysql 1 to 2 replication test another row |
+----+-------------------------------------------+
2 rows in set (0.00 sec)

Step 4 - Setup replication between mysql2 and mysql1

Point the slave mysql1 to master mysql2

On mysql1, in this step, we will need:

Then run the below on the MySQL prompt replacing the values with your values:

slave stop;
CHANGE MASTER TO MASTER_HOST = 'mysql2', MASTER_USER = 'replicator', MASTER_PASSWORD = 'aComplexPassword', MASTER_LOG_FILE = 'mysql-bin.000003',  MASTER_LOG_POS = 107;

Start replication

After doing the above, start the slave on mysql1 then show the status of the replication relationship

slave start;
show slave status;

Test mysql2 to mysql1 replication

On mysql2, then insert a couple of rows

insert into exampledb.dummy SET data='mysql 2 to 1 replication test';
insert into exampledb.dummy SET data='mysql 2 to 1 replication test another row';

Once you do that and do a select * from exampledb.dummy on mysql1 you should find the rows nicely waiting for you:

mysql> select * from exampledb.dummy;
+----+-------------------------------------------+
| id | data                                      |
+----+-------------------------------------------+
|  1 | mysql 1 to 2 replication test             |
|  3 | mysql 1 to 2 replication test another row |
|  4 | mysql 2 to 1 replication test             |
|  6 | mysql 2 to 1 replication test another row |
+----+-------------------------------------------+
4 rows in set (0.00 sec)

Step 5 - Load balance between mysql1 and mysql2

Now that we have setup the Master-Master replication between mysql1 and mysql2, we need to ensure that applications using this database always find a healthy replica.

There are a couple of ways to do this, one of them being setting up another Virtual Machine running HAProxy for example or in our case, I'm going to make use of the Azure Load Balancer that comes with the Cloud Service to setup load balancing.

Note that in this setup, I'm going to expose my MySQL database to the internet over a public endpoint (3306), I could apply ACL to the endpoint to allow only specific IP addresses to connect, or I can make use of the Internal Azure Load balancer. For the purpose of this blog post, I'll just leave it public.

Create Load balanced set on mysql1

Let's go back to our portal, click on the mysql1 VM, scroll down to Load balanced sets and click there, then click on Join, then Configure required settings.
Setting up load balanced set

Then Create new with Public and Private ports 3306, specify a 6 second interval and 2 retries before considering node unavailable then save and wait for the set to show in the table.
Settings for load balanced set

Join the same Load balanced set on mysql2

Repeat the same procedure for mysql2 but instead of creating a new set, join the previously created one.
Join load balanced set

Step 6 - Test load balancing

Additionally, for the purpose of the blog post, on both servers, run:

grant all privileges on *.* to 'root'@'%' identified by 'aComplexPassword';
flush privileges;

which essentially allows the root user to connect remotely.

You should now be able to connect to your MySQL "farm" on
mysqlha.cloudapp.net:3306 so test it from any machine and do a show variables like "server_id" to get

+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| server_id     | 2     |
+---------------+-------+
1 row in set (0.00 sec)

if you disconnect and connect again, you might get

+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| server_id     | 1     |
+---------------+-------+
1 row in set (0.00 sec)

Step 6 - Test Fail over

Now Shutdown one of the VMs (for example mysql2) on Azure and try to connect to mysqlha.cloudapp.net and insert a couple of rows.

+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| server_id     | 1     |
+---------------+-------+
1 row in set (0.00 sec)

mysql> insert into exampledb.dummy SET data='mysql 1 is up, testing failover';

Now Start the mysql2 VM again and directly connect to it's MySQL instance, then select * from exampledb.dummy. You should find the row inserted while the instance was offline synced:

+----+-------------------------------------------+
| id | data                                      |
+----+-------------------------------------------+
|  1 | mysql 1 to 2 replication test             |
|  3 | mysql 1 to 2 replication test another row |
|  4 | mysql 2 to 1 replication test             |
|  6 | mysql 2 to 1 replication test another row |
|  7 | Testing Load balancing                    |
|  8 | Testing Load balancing 2                  |
|  9 | mysql 1 is up, testing failover           |
+----+-------------------------------------------+
7 rows in set (0.00 sec)
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