Use digidevice.appmonitor to monitor your application

The appmonitor Python module allows you to monitor the health of your Python application and take action on failure.

The application monitor daemon acts as a system service, allowing external applications to register with the daemon , and the daemon will take a specific action when a registered application does not refresh the daemon within the refresh timeout. The daemon can be configured to:

Application monitor workflow

  1. The application registers with the application monitor daemon. In this step, the application must provide:

    • The refresh timeout.

    • The action to take in case of failure.

    • The restart command to execute in the case the application will be restarted.

  2. The daemon stores the registered application information and begins monitoring the application refresh time.

  3. The application periodically sends a refresh request to the daemon. The time between refresh requests should be lower than the configured refresh timeout.

  4. If the application does not send a refresh request during the configured timeout, the daemon executes the action specified when the application was registered.

The application can stop the monitoring process at any time by sending an unregister request to the daemon.

digidevice.appmonitor API

This API provides all the required methods and objects to access and interact with the application monitor daemon.

Register the application

The first step to start using the application monitor daemon is to register the application in it. To do so, the appmonitor module provides the register_app method:

Method register_app(timeout, action, restart_command)
Description Registers a new application to the application monitor daemon with the provided data.
Parameters

  • timeout: Maximum amount of time -in milliseconds- to wait without a refresh before executing the action.

  • action: An AppMonitorAction to execute when the application has not contacted the service within the timeout period. Must be one of:

    • AppMonitorAction.KILL: Terminates the application.

    • AppMonitorAction.RESTART: Restarts the application using the provided command.

    • AppMonitorAction.REBOOT: Reboots the device.

  • restart_command: Command to execute when AppMonitorAction.RESTART action is used. None by default.
Returns

An AppMonitorHandler object to use to refresh or unregister the application from the Application Monitor daemon.

Raises

  • ValueError if timeout, or action is not valid.

  • AppMonitorError if there is an error registering the application.

Usage example:

from digidevice import appmonitor
from digidevice.appmonitor import AppMonitorAction
		
...
		
mon_handle = appmonitor.register_app(5000, AppMonitorAction.KILL)
#mon_handle = appmonitor.register_app(5000, AppMonitorAction.REBOOT)
#mon_handle = appmonitor.register_app(5000, AppMonitorAction.RESTART, "<restart_command>")

Refresh the application

After the application has been registered, it must start sending refresh requests to the application monitor daemon, using the refresh() method of the received application monitor handler. The time between the refresh calls should not be longer than the timeout specified in the registration process; otherwise, the daemon will execute the registered action.

Method refresh()
Description Refreshes the application in the application monitor daemon.
Parameters None.
Returns

None.
Raises

AppMonitorError if there is an error refreshing the application.

Usage example:

import time
	
...

while True:
  mon_handle.refresh()
  time.sleep(1)

Unregister the application

The application can be unregistered from the application monitor daemon at any time by calling the unregister function of the the received application monitor handler.

Method unregister()
Description Unregisters the application from the application monitor daemon.
Parameters None.
Returns

None.
Raises

AppMonitorError if there is an error unregistering the application.

Usage example:

...

mon_handle.unregister()