A cron job runner with self-healing and job dependencies.
License: MPL 2
How to run tests
First you need to create a dedicated test database. We recommend you
test_crontabber. Then you need the necessary credentials for
Before running the tests you need to install some extras to be able to run tests at all:
pip install -r test-requirements.txt
Next, in the root directory of the project create a file called
test-crontabber.ini and it should look something like this:
[crontabber] user=myusername password=mypassword dbname=test_crontabber
To start all the tests run:
If you want to run a specific test in a specific file in a specific
class you can define it per the
nosetests standard like this for
PYTHONPATH=. nosetests tests crontabber/tests/test_crontabber.py:TestCrontabber.test_basic_run_job
If you want the tests to stop as soon as the first test fails add
to that same command above.
Also, if you want
nosetests to not capture
to that same command as above.
How to do code coverage analysis
First you need to install the
coverage module. Then,
nosetests, you can run this:
PYTHONPATH=. nosetests --with-coverage --cover-erase --cover-html --cover-package=crontabber
After it has run, you can open the file
cover/index.html in browser.
How to run the exampleapp
The example app helps you set up a playground to play around with and test crontabber to gain a better understanding of how it works.
The best place to start with is to read the
file and go through its steps. Once you get the basics to work you can
start experimenting with adding your job classes.
How locking works
crontabber supports locking. It basically means if you start a second instance of crontabber whilst it's already ongoing in another terminal/server the second one will exist early. This is only applicable if there is an actual job ongoing.
There are two kinds of locking.
- General locking. The first thing crontabber does before it starts
an app is to ask the state (stored in PostgreSQL) if it's ongoing and
if it is, it exists with an error code of
- Sub-second locking. If the general locking (see point above) says
"No, the job is not ongoing", it's going to proceed to update the
state with a row-level locking transaction in
That basically means PostgreSQL only allows one single
UPDATEfrom the process that gets there first. The second crontabber process will will exit early with an error code of
2if the first crontabber process managed to run the
Imagine two separate terminals starting crontabber at the almost same time:
# Terminal 1 $ python crontabber.py --admin.conf=crontabber.ini $ echo $? 0
# Terminal 2 (started almost simultaneously) $ python crontabber.py --admin.conf=crontabber.ini $ echo $? 3
Note! If a job has been ongoing to a maximum period of time, the
locking is ignored. This is controlled by the config option
crontabber.max_ongoing_age_hours which defaults to 12 hours.
This is applicable if crontabber, updates the state that it's starting a
job, then when it tries to update the state that it finished
(successfully or not) and that write fails, if for example it's unable
to make a connection to PostgreSQL. If this happens crontabber will just
ignore the lock and run it anyway.