Daemonising Celery and Flower on Windows - Legacy

To ensure that the Celery task queue and Flower are started at system start-up it is advisable to launch them using batch files and configure Windows Task Scheduler to run each of these at system start-up.

Celery will sometimes fall over during the execution of a long task. If Celery frequently falls over on your system then Windows Task Scheduler can be used to restart Celery on a regular basis. The Task Scheduler can also be used to ensure celery is running a few minutes prior to scheduled PACS queries.

An example batch file is shown below for running and restarting Celery. This calls separate batch files to start Celery and Flower, also shown below.

Celery control batch file

celery_task.bat, to be run as a scheduled task.

:: Create variables containing the name and path of the Celery pid file and the
:: names and paths to the batch files used to run Celery and Flower.
SET celeryPidFile=E:\media_root\celery\default.pid
SET celeryStartFile=D:\Server_Apps\celery\celery_start.bat
SET flowerStartFile=D:\Server_Apps\flower\flower_start.bat

:: Celery 3.1.25 cannot be shutdown gracefully, and has to be killed. The
:: following command will kill all celery.exe processes and any python.exe
:: processes associated with Celery. The celery.exe process that is running
:: Flower will also be killed by this command.
TASKKILL /IM celery.exe /T /F

:: Force the deletion of the Celery pid file so that Celery can be restarted.
DEL /F "%celeryPidFile%"

:: Start Flower again.
START /B CMD /C CALL "%flowerStartFile%"

:: Start Celery again.
START /B CMD /C CALL "%celeryStartFile%"

Celery start batch file

celery_start.bat, called by celery_task.bat.

:: Create variables containing the drive and path to OpenREM and the name and
:: path of the Celery pid and log files.
SET openremDrive=D:
SET openremPath=D:\Server_Apps\python27\Lib\site-packages\openrem
SET celeryPidFile=E:\media_root\celery\default.pid
SET celeryLogFile=E:\media_root\celery\default.log

:: Change to the drive on which OpenREM is installed and navigate to the
:: OpenREM folder.
%openremDrive%
CD "%openremPath%"

:: Start Celery.
celery worker -n default -Ofair -A openremproject -c 4 -Q default --pidfile=%celeryPidFile% --logfile=%celeryLogFile%

Flower start batch file

flower_start.bat, called by celery_task.bat and also used to start Flower at system start-up.

:: Create variables containing the drive and path to OpenREM and the name and
:: path of the Flower log file and the Flower port.
SET openremDrive=D:
SET openremPath=D:\Server_Apps\python27\Lib\site-packages\openrem
SET flowerLogFile=E:\media_root\celery\flower.log
SET flowerPort=5555

:: Change to the drive on which OpenREM is installed and navigate to the
:: OpenREM folder.
%openremDrive%
CD "%openremPath%"

:: Start Flower using Celery.
celery -A openremproject flower --port="%flowerPort%" --loglevel=info --log-file-prefix="%flowerLogFile%"

Setting up a scheduled task

For Celery

Open Task Scheduler on the OpenREM server and then click on the Task Scheduler Library item in the left-hand pane. This should look something like figure 1 below, but without the OpenREM tasks present.

Task scheduler overview

Figure 1: An overview of Windows Task Scheduler

To create a new task for celery click on Create Task... in the Actions menu in the right-hand pane. Give the task a name and description. Next, click on the Change User or Group button and type system in to the box, then click Check Names, then click OK. This sets the server’s SYSTEM user to run the task. Also check the Run with highest prilileges box. Your task should now look similar to figure 2.

Task scheduler overview

Figure 2: General properties

Next, click on the Triggers tab so that you can set when the task will be run. As a minimum you should add an At startup trigger. To do this, click New.... In the dialogue box that appears select At startup from the Begin the task options and ensure that the Enabled checkbox is selected. Then click OK. You may wish to add other triggers that take place at specific times during the day, as shown in figure 3.

In the example shown in figure 3 celery is started at system start up, and restarted multiple times each day to ensure that it is running before any PACS queries. Your requirements may be more straightforward than this example.

Task scheduler overview

Figure 3: Trigger properties

Now click on the Actions tab so that you can add the action that is taken when the task is run. Click on New..., and in the dialogue box that appears select Start a program as the Action. Click on Browse and select the celery batch file that you created earlier. Click OK to close the New Action dialogue box. Figure 4 shows an example of the the Actions tab.

Task scheduler overview

Figure 4: Action properties

There are no particular conditions set for the task, as shown in figure 5.

Task scheduler overview

Figure 5: Condition properties

Finally, click on the Settings tab (figure 6). Check the Allow task to be run on demand box, and also the If the running task does not end when requested, force it to stop box. Choose Stop the existing instance from the If the task is already running, then the following rule applies: list. Then click the OK button to add the task to the scheduler library.

Task scheduler overview

Figure 6: Task settings

For Flower

Repeat the above steps for the Flower batch file, but only configure the Flower task to trigger on system start-up: there should be no need to schedule re-starts of Flower.