django-orchestra/docs/create-services.md

# Creating New Services

1. Think about if the service can fit into one of the existing service models like: SaaS or WebApps, refere to the related documentation if that is the case.
2. Create a new django app using `startapp` management command. For ilustrational purposes we will create a crontab services that will allow orchestra to manage user-based crontabs.
    ```bash
    python3 manage.py startapp crontabs
    ```
3. Add the new *crontabs* app to the `INSTALLED_APPS` in your project's `settings.py`
3. Create a `models.py` file with the data your service needs to keep in order to be managed by orchestra
    ```python
    from django.db import models
    
    class CrontabSchedule(models.Model):
        account = models.ForeignKey('accounts.Account', verbose_name=_("account"))
        minute = models.CharField(_("minute"), max_length=64, default='*')
        hour = models.CharField(_("hour"), max_length=64, default='*')
        day_of_week = models.CharField(_("day of week"), max_length=64, default='*')
        day_of_month = models.CharField(_("day of month"), max_length=64, default='*')
        month_of_year = models.CharField(_("month of year"), max_length=64, default='*')
        
        class Meta:
            ordering = ('month_of_year', 'day_of_month', 'day_of_week', 'hour', 'minute')
        
        def __str__(self):
            rfield = lambda f: f and str(f).replace(' ', '') or '*'
            return "{0} {1} {2} {3} {4} (m/h/d/dM/MY)".format(
                rfield(self.minute), rfield(self.hour), rfield(self.day_of_week),
                rfield(self.day_of_month), rfield(self.month_of_year),
            )
    
    class Crontab(models.Model):
        account = models.ForeignKey('accounts.Account', verbose_name=_("account"))
        schedule = models.ForeignKey(CrontabSchedule, verbose_name=_("schedule"))
        description = models.CharField(_("description"), max_length=256, blank=True)
        command = models.TextField(_("content"))
        
        def __str__(self):
            return (self.description or self.command)[:32]
    ```

4. Create a `admin.py` to enable the admin interface, refere to [Django Admin documentation](https://docs.djangoproject.com/en/1.9/ref/contrib/admin/) for further customization.
    ```python
    from django.contrib import admin
    from .models import CrontabSchedule, Crontab

    class CrontabScheduleAdmin(admin.ModelAdmin):
        pass

    class CrontabAdmin(admin.ModelAdmin):
        pass

    admin.site.register(CrontabSchedule, CrontabScheduleAdmin)
    admin.site.register(Crontab, CrontabAdmin)
    ```

5. Create a `api.py` to enable the REST API.

6. Create a `backends.py` fiel with the needed backends for service orchestration and monitoring.
    ```python
    import os
    import textwrap
    from django.utils.translation import gettext_lazy as _
    from orchestra.contrib.orchestration import ServiceController, replace
    from orchestra.contrib.resources import ServiceMonitor
    
    class UNIXCronBackend(ServiceController):
        """
        Basic UNIX cron support.
        """
        verbose_name = _("UNIX cron")
        model = 'crons.CronTab'
        
        def prepare(self):
            super(UNIXCronBackend, self).prepare()
            self.accounts = set()
        
        def save(self, crontab):
            self.accounts.add(crontab.account)
        
        def delete(self, crontab):
            self.accounts.add(crontab.account)
        
        def commit(self):
            for account in self.accounts:
                crontab = None
                self.append("echo '' > %(crontab_path)s" % context)
                for crontab in account.crontabs.all():
                    self.append("
    ```
7. Configure the routing