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.

   python3 manage.py startapp crontabs

3. Add the new crontabs app to the INSTALLED_APPS in your project's settings.py

4. Create a models.py file with the data your service needs to keep in order to be managed by orchestra

   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]

5. Create a admin.py to enable the admin interface, refere to Django Admin documentation for further customization.

   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)

6. Create a api.py to enable the REST API.

7. Create a backends.py fiel with the needed backends for service orchestration and monitoring.

   import os
   import textwrap
   from django.utils.translation import ugettext_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("

8. Configure the routing