How to enable a virtualenv in a systemd service unit?

Question

I want to "activate" a virtualenv in a systemd service file.

I would like avoid to have a shell process between the systemd process and the python interpreter.

My current solution looks like this:

[Unit]
Description=fooservice
After=syslog.target network.target

[Service]
Type=simple
User=fooservice
WorkingDirectory={{ venv_home }}
ExecStart={{ venv_home }}/fooservice --serve-in-foreground
Restart=on-abort
EnvironmentFile=/etc/sysconfig/fooservice.env

[Install]
WantedBy=multi-user.target

/etc/sysconfig/fooservice.env

PATH={{ venv_home }}/bin:/usr/local/bin:/usr/bin:/bin
PYTHONIOENCODING=utf-8
PYTHONPATH={{ venv_home }}/...
VIRTUAL_ENV={{ venv_home }}

But I am having trouble. I get ImportErrors since some enties in sys.path are missing.

Solution 1

The virtualenv is "baked into the Python interpreter in the virtualenv". This means you can launch python or console_scripts directly in that virtualenv and don't need to activate the virtualenv first or manage PATH yourself.:

ExecStart={{ venv_home }}/bin/fooservice --serve-in-foreground

or

ExecStart={{ venv_home }}/bin/python {{ venv_home }}/fooservice.py --serve-in-foreground

and remove the EnvironmentFile entry.

To verify that it is indeed correct you can check sys.path by running

{{ venv_home }}/bin/python -m site

and comparing the output to

python -m site

Solution 2

While the path for libraries is indeed baked into the python interpreter of the virtualenv, I've had issues with python tools that were using binaries installed in that virtualenv. For instance, my apache airflow service wouldn't work because it couldn't find the gunicorn binary. To work around this, here's my ExecStart instruction, with an Environment instruction (which sets an environment variable for the service alone).

ExecStart={{ virtualenv }}/bin/python {{ virtualenv }}/bin/airflow webserver
Environment="PATH={{ virtualenv }}/bin:{{ ansible_env.PATH }}"

ExecStartexplicitly uses the python interpreter of the virtualenv. I'm also adding a PATH variable, which adds the binary folder of the virtualenv before the system PATH. That way, I get the desired python libraries as well as binaries.

Note that I'm using ansible to build this service, ergo the curly braces of jinja2.

Solution 3

In my case I just tried to add environment variables required for Flask, for instance

[Service]
Environment="PATH=/xx/yy/zz/venv/bin"
Environment="FLASK_ENV=development"
Environment="APP_SETTINGS=config.DevelopmentConfig"

I was using virtualenv so /xx/yy/zz/venv/bin is the path of virtualenv folder.

Solution 4

I'm not using virtualenv but pyenv: here is it just to use the real .pyenv path in the shebang and make sure it is in the PATH

Ex: pyenv activate flask-prod for user mortenb which is running in prod

/home/mortenb/.pyenv/versions/flask-prod/bin/python --version
Python 3.6.2

Then to my flask scripts starting in systemd *.service I add the following shebang:

#!/home/mortenb/.pyenv/versions/flask-prod/bin/python3

View more solutions

Comments

[guettli]

Yes, sys.path is correct. Thank you. I checked the difference between os.environ. It seems that VIRTUAL_ENV is not set, if I use {{ venv_home }}/bin/python. Can this make trouble?

[Nils Werner]

I don't know for certain but I have never had issues with VIRTUAL_ENV not being set.

[stelios]

good point Nils. Btw, fooservice.py doesn't make sense to be inside venv_home directory, I suppose its a typo in the question.

[Mark Edington]

Note the suggested print commands are not compatible with Python 3. If you are using at least python 2.4, you can alternatively just use: python -m site to get a nicely formatted output of the sys.path variable along with additional information.

[Nils Werner]

Neat, I didn't know about python -m site. I have adjusted my answer.

[Shubham Namdeo]

Worked like a charm for me. Thanks.

[Jason R. Coombs]

This approach doesn't work when the python process you're starting expects the virtualenv to be activated. For example, consider {{ venv_home }}/bin/python -m newrelic.admin run-program python -m myapp. That will launch python in the venv, invoke New Relic, and then it will fail to launch the app because python is not in the path because the venv is not activated.

[Nils Werner]

Have you tried {{ venv_home }}/bin/python -m newrelic.admin run-program {{ venv_home }}/bin/python -m myapp?

[brainstorm]

Also appears to fail with python3 when the (python3 -mvenv created) venv has third party modules not in the python3 stdlib? See here: gist.github.com/brainstorm/bff8b439072ffadbd95ae901c659a6b5

[Nils Werner]

@brainstorm I cannot reproduce your issues on OSX: gist.github.com/nils-werner/d98aff2b865dac9375570340ce635844‌​. Maybe it has to with pcgr

[brainstorm]

@NilsWerner I ended up solving it by spawning a shell, nothing else worked on Ubuntu 17.10: github.com/umccr/pcgr-deploy/blob/master/ansible/files/… ... please ignore the jinja2 templating for ansible, it expands correctly when deployed.

[ankostis]

For those wondering if this is ninja2....no, the double curly-braces are just placeholders the OP invented: superuser.com/questions/1209919/…

[Shankara Narayana]

what exactly does --serve-in-foreground do?

[Nils Werner]

That's a parameter of the Python server the OP invented.

[FilBot3]

When I use the {{ venv_home }} syntax, I get errors that it's not a path.

[pyFiddler]

Literally came looking for how to set the environment in a service because airflow couldn't find gunicorn. Was NOT disappointed! Thank you! I'm up and running.

[Manju N]

Exactly , I was in need of Airflow automation through Ansible . Thank you so much :)