I'd just like to share a few hard-won tips for writing pulsar functions
in python.
(1) Pulsar is hard-wired to start "python" not "python3". I hope this
will change <https://github.com/apache/pulsar/issues/5518>, but until
then there is a very risky workaround on Ubuntu:
|sudo update-alternatives --install /usr/bin/python python
/usr/bin/python3 10|
Only do this on a system where python(2) is *not* installed and you are
sure you will never install it - not even as a dependency of some other
package. If it's a VM dedicated to pulsar you may be OK.
(2) If a python function crashes at startup, you won't see its stderr
output from the "localrun" command or the pulsar daemon. But you *will*
find it logged to
apache-pulsar-2.4.1/logs/functions/<tenant>/<namespace>/<function>/<function>-<n>.log
(3) If you have a python function which includes a class, e.g.
/home/ubuntu/func1.py contains class FirstFunction, then you have to
start it like this:
--py /home/ubuntu/func1.py --class func1.FirstFunction
(that is, "func1" appears twice). I didn't see any example like this in
the documentation, and you don't get much help if you get it wrong! :-)
It works by adding the dirname (/home/ubuntu in this case) to sys.path.
Hope this helps someone else.
Cheers,
Brian.
