Installation | Maintenance | Beyond Lino

The Lino Daemon with django-channels, an extension to the notification framework

This document explains why and how to configure a lino daemon process and also the capabilities of the lino.modlib.linod plugin.

A Lino application can declare background tasks. Such tasks run in the background, i.e. as a service in another process than the web server. That other process listens over channel protocol (provided by django-channels).

runworker linod_myprj

Starts a long-running process that by default only listens for immediate desktop notifications which it sends when found.

It also has the capabilities to run scheduled jobs and logging non-lino log entries. Run the following command to enable these functionalities.

$ python manage.py initiate_linod

On a development machine you simply run these commands in separate terminals. On a production server we recommend to run this as a daemon via Supervisor as described below.

This feature requires redis and the following python packages to be installed: django-channels, channels_redis.

As an application developer you define background tasks using dd.schedule_often and dd.schedule_daily. For example the send_pending_emails_often and clear_seen_messages of the lino.modlib.notify plugin.

use_linod

To enable this feature, you must set use_linod to True. This is usually done by the application developer, but this decision can be overridden by a system admin in a local settings.py file.

configure_linod

Additionally to having use_linod set to True, you must also set the supervisor configurations by doing configure_linod and restart supervisor using the command with sudo or root privilege:

$ service supervisor restart

The getlino configure --linod option specifies that every new Lino site will automatically configure a lino daemon process in the supervisor as a service.

Activating the feature

>>> from atelier.sheller import Sheller
>>> shell = Sheller("lino_book/projects/roger")
>>> shell("python manage.py linod")
This site does not use linod.

As a site maintainer you can check whether your application has scheduled background jobs by issuing the following command in your project directory:

$ python manage.py linod --dry-run

For example in the noi1e demo project there are 6 jobs:

>>> shell = Sheller("lino_book/projects/noi1e")
>>> shell("python manage.py linod --dry-run")
... 
# TODO

Installation instructions

This section has become useless because these things are now done automatically by getlino.

• Install the Supervisor package:

  $ sudo apt install supervisor
  

  The supervisor package is being installed system-wide, it is not related to any specific project.

• Create a file linod_myprj.conf in /etc/supervisor/conf.d/ with this content (given the context provided below):

  [program:linod_{{project_name}}]
  environment=
      DJANGO_SETTINGS_MODULE={{settings_module}}
  directory={{project_path}}
  command=/bin/bash -c "source {{env_activate}} && python manage.py runworker {{channels}}"
  stopsignal=KILL
  killasgroup=true
  priority=998
  startsecs=5
  username = www-data
  umask = 002
  
  [program:initiate_linod_{{project_name}}]
  environment=
      DJANGO_SETTINGS_MODULE={{settings_module}}
  directory={{project_path}}
  command=/bin/bash -c "source {{env_activate}} && python manage.py initiate_linod"
  autorestart=false
  priority=999
  username = www-data
  umask = 002
  

• Context to fill out the above template (a dictionary mapping with example and a comment as description):

  {
      'project_name': "myprj", # The name of your project
      'settings_module': "settings", # If you have a settings.py in your project's directory
      'project_path': "~/lino/lino_local/myprj", # The path at which your project is located
      'env_activate': "~/lino/lino_local/myprj/env/bin/activate", # The path to the binary that activates your project's python virtual environment
      'channels': "linod_myprj", # The name for linod with the prefix 'linod_' and your project name as the suffix, you can also add any additional channels.consumer.${"Sync"|"Async"}Consumer subclasses separated by a whitespace
  }
  

• Restart supervisord:

  $ sudo service supervisor restart
  

• Have a look at the log files in /var/log/supervisor.