MaxScale/Documentation/Tutorials/Galera-Cluster-Connection-Routing-Tutorial.md

# Connection Routing with Galera Cluster

# Environment & Solution Space

The object of this tutorial is to have a system that has two ports available,
one for write connections to the database cluster and the other for read
connections to the database.

## Setting up MariaDB MaxScale

The first part of this tutorial is covered in [MariaDB MaxScale Tutorial](MaxScale-Tutorial.md).
Please read it and follow the instructions for setting up MariaDB MaxScale with
the type of cluster you want to use.

Once you have MariaDB MaxScale installed and the database users created, we can
create the configuration file for MariaDB MaxScale.

## Creating Your MariaDB MaxScale Configuration

MariaDB MaxScale reads its configuration from `/etc/maxscale.cnf`. A template
configuration is provided with the MaxScale installation.

A global, `[maxscale]`, section is included within every MariaDB MaxScale
configuration file; this is used to set the values of various MariaDB MaxScale
wide parameters, perhaps the most important of these is the number of threads
that MariaDB MaxScale will use to handle client requests.

```
[maxscale]
threads=4
```

Since we are using Galera Cluster and connection routing we want a single to
which the client application can connect; MariaDB MaxScale will then route
connections to this port onwards to the various nodes within the Galera
Cluster. To achieve this within MariaDB MaxScale we need to define a service in
the ini file. Create a section for each in your MariaDB MaxScale configuration
file and set the type to service, the section name is the names of the service
and should be meaningful to the administrator. Names may contain whitespace.

```
[Galera Service]
type=service
```

The router for this section the readconnroute module, also the service should be
provided with the list of servers that will be part of the cluster. The server
names given here are actually the names of server sections in the configuration
file and not the physical hostnames or addresses of the servers.

```
[Galera Service]
type=service
router=readconnroute
servers=dbserv1, dbserv2, dbserv3
```

In order to instruct the router to which servers it should route we must add
router options to the service. The router options are compared to the status
that the monitor collects from the servers and used to restrict the eligible set
of servers to which that service may route. In our case we use the option that
restricts us to servers that are fully functional members of the Galera cluster
which are able to support SQL operations on the cluster. To achieve this we use
the router option synced.

```
[Galera Service]
type=service
router=readconnroute
router_options=synced
servers=dbserv1, dbserv2, dbserv3
```

The final step in the services section is to add the username and password that
will be used to populate the user data from the database cluster. There are two
options for representing the password, either plain text or encrypted passwords
may be used.  In order to use encrypted passwords a set of keys must be
generated that will be used by the encryption and decryption process. To
generate the keys use the `maxkeys` command and pass the name of the secrets
file in which the keys are stored.

```
maxkeys /var/lib/maxscale/.secrets
```

Once the keys have been created the maxpasswd command can be used to generate
the encrypted password.

```
maxpasswd plainpassword
96F99AA1315BDC3604B006F427DD9484
```

The username and password, either encrypted or plain text, are stored in the
service section using the user and passwd parameters.

```
[Galera Service]
type=service
router=readconnroute
router_options=synced
servers=dbserv1, dbserv2, dbserv3
user=maxscale
passwd=96F99AA1315BDC3604B006F427DD9484
```

This completes the definitions required by the services, however listening ports
must be associated with the services in order to allow network connections. This
is done by creating a series of listener sections. These sections again are
named for the convenience of the administrator and should be of type listener
with an entry labeled service which contains the name of the service to
associate the listener with. Each service may have multiple listeners.

```
[Galera Listener]
type=listener
service=Galera Service
```

A listener must also define the protocol module it will use for the incoming
network protocol, currently this must be the `MariaDBClient` protocol for all
database listeners. The listener must also supply the network port to listen on.

```
[Galera Listener]
type=listener
service=Galera Service
protocol=MariaDBClient
port=4306
```

An address parameter may be given if the listener is required to bind to a
particular network address when using hosts with multiple network addresses. The
default behavior is to listen on all network interfaces.

## Configuring the Monitor and Servers

The next step is the configuration of the monitor and the servers that the
service uses. This is process described in the
[Configuring Galera Monitor](Configuring-Galera-Monitor.md) document.

## Configuring the Administrative Interface

The MaxAdmin configuration is described in the
[Configuring MaxAdmin](Configuring-MaxAdmin.md) document.

## Starting MariaDB MaxScale

Upon completion of the configuration process MariaDB MaxScale is ready to be
started for the first time. For newer systems that use systemd, use the _systemctl_ command.

```
sudo systemctl start maxscale
```

For older SysV systems, use the _service_ command.

```
sudo service maxscale start
```

If MaxScale fails to start, check the error log in `/var/log/maxscale/` to see
if any errors are detected in the configuration file. The `maxadmin` command may
be used to confirm that MariaDB MaxScale is running and the services, listeners
etc have been correctly configured.

```
% sudo maxadmin list services

Services.
--------------------------+----------------------+--------+---------------
Service Name              | Router Module        | #Users | Total Sessions
--------------------------+----------------------+--------+---------------
Galera Service            | readconnroute        |      1 |     1
CLI                       | cli                  |      2 |     2
--------------------------+----------------------+--------+---------------
% sudo maxadmin list servers
Servers.
-------------------+-----------------+-------+-------------+-------------------
Server             | Address         | Port  | Connections | Status
-------------------+-----------------+-------+-------------+--------------------
dbserv1            | 192.168.2.1     |  3306 |           0 | Running, Synced, Master
dbserv2            | 192.168.2.2     |  3306 |           0 | Running, Synced, Slave
dbserv3            | 192.168.2.3     |  3306 |           0 | Running, Synced, Slave
-------------------+-----------------+-------+-------------+--------------------
```

A Galera Cluster is a multi-master clustering technology, however the monitor is able
to impose false notions of master and slave roles within a Galera Cluster in order to
facilitate the use of Galera as if it were a standard MariaDB Replication setup.
This is merely an internal MariaDB MaxScale convenience and has no impact on the behavior of the cluster.

You can control which Galera node is the master server by using the _priority_
mechanism of the Galera Monitor module. For more details,
read the [Galera Monitor](../Monitors/Galera-Monitor.md) documentation.

```
% sudo maxadmin list listeners

Listeners.
---------------------+--------------------+-----------------+-------+--------
Service Name         | Protocol Module    | Address         | Port  | State
---------------------+--------------------+-----------------+-------+--------
Galera Service       | MariaDBClient      | *               |  4306 | Running
CLI                  | maxscaled          | localhost       |  6603 | Running
---------------------+--------------------+-----------------+-------+--------
%
```

MariaDB MaxScale is now ready to start accepting client connections and routing
them to the cluster. More options may be found in the
[Configuration Guide](../Getting-Started/Configuration-Guide.md)
and in the router module documentation.

More detail on the use of `maxadmin` can be found in the
[MaxAdmin](../Reference/MaxAdmin.md) document.