# MariaDB

This directory contains a simple systemd service for running an instance of MariaDB 10.6.

## Deployment and Use

Including the `spec.bu` file here in your host configuration is enough to have MariaDB enabled on the
system -- no other configuration is needed. The following commands will manage the service
accordingly:

  - Starting MariaDB: `sudo systemctl start mariadb`
  - Stopping MariaDB: `sudo systemctl stop mariadb`
  - Getting logs for the running service: `journalctl -feu mariadb`

By default, MariaDB listens on the `internal` network under the `mariadb` hostname, port 3306. Any
services that wish to connect to MariaDB for that hostname and port need to also be included in the
`internal` network.

The systemd service for MariaDB tries to delay readiness checks for until the listener is correctly
set up, and will run periodic health-checks to ensure the same.

## Use

Depending on MariaDB from other systemd services is as simple as declaring an ordered dependency in
the systemd service file, for example:

```ini
[Unit]
Description=Service That Uses MariaDB
Wants=container-build@example.service mariadb.service
After=container-build@example.service mariadb.service
```

MariaDB will then be guaranteed to be running before the example service is.

## Database Migrations

Services can define an initial state for databases used internally by way of special
`mariadb-migrate.sql` files, which are used by the included `mariadb-migrate@` service. 

For example, given a service `example` (in its own directory), we would need a file
`example/service/mariadb-migrate.sql`, containing SQL calls for creating databases, users:

```sql
-- Create default database.
CREATE DATABASE IF NOT EXISTS `${EXAMPLE_DATABASE_NAME}`;

-- Create default user with pre-defined password.
CREATE USER IF NOT EXISTS '${EXAMPLE_DATABASE_USERNAME}'@'%' IDENTIFIED BY '${EXAMPLE_DATABASE_PASSWORD}';
GRANT ALL PRIVILEGES ON `${EXAMPLE_DATABASE_NAME}`.* TO '${EXAMPLE_DATABASE_USERNAME}'@'%';
```

As evidenced above, this file can also have environment variables defined, which are derived from the
service-specific `example/example.env.template` file (if any exists). Running these migrations is as
simple a matter as running the aforementioned service, e.g.:

```
sudo systemctl start mariadb-migrate@example 
```

The systemd journal should provide evidence of execution and reference to any issues that may have occured.