airflow systemd fails due to gunicorn - gunicorn

Question

I am unable to start the airflow webserver using systemd even though it starts and functions properly outside of systemd like so:
export AIRFLOW_HOME=/path/to/my/airflow/home ; airflow webserver -p 8080
The systemd log leads me to believe that the issue comes from gunicorn, even though gunicorn starts without issue when I run the above command (i.e. it's only an issue in systemd). I have configured the following systemd files according to the airflow docs (running Ubuntu 16).
/etc/default/airflow
AIRFLOW_HOME=/path/to/my/airflow/home
SCHEDULER_RUNS=5
/lib/systemd/system/airflow-webserver.service
[Unit]
Description=Airflow webserver daemon
After=network.target
[Service]
EnvironmentFile=/etc/default/airflow
User=ubuntu
Group=ubuntu
Type=simple
ExecStart=/bin/bash -c "export AIRFLOW_HOME=/path/to/my/airflow/home ; airflow webserver -p 8080 "
Restart=on-failure
RestartSec=5s
PrivateTmp=true
[Install]
WantedBy=multi-user.target
/etc/tmpfiles.d/airflow.conf
D /run/airflow 0755 airflow airflow
This results in the following error when I start the service with systemctl.
systemctl start airflow-webserver.service
Jul 15 22:41:27 ip-172-31-19-64 systemd[1]: Started Airflow webserver daemon.
Jul 15 22:41:27 ip-172-31-19-64 bash[31494]: [2018-07-15 22:41:27,555] {driver.py:120} INFO - Generating grammar tables from /usr/lib/python3.5/lib2to3/Grammar.txt
Jul 15 22:41:27 ip-172-31-19-64 bash[31494]: [2018-07-15 22:41:27,592] {driver.py:120} INFO - Generating grammar tables from /usr/lib/python3.5/lib2to3/PatternGrammar.txt
Jul 15 22:41:27 ip-172-31-19-64 bash[31494]: [2018-07-15 22:41:27,729] {__init__.py:45} INFO - Using executor SequentialExecutor
Jul 15 22:41:28 ip-172-31-19-64 bash[31494]: ____________ _____________
Jul 15 22:41:28 ip-172-31-19-64 bash[31494]: ____ |__( )_________ __/__ /________ __
Jul 15 22:41:28 ip-172-31-19-64 bash[31494]: ____ /| |_ /__ ___/_ /_ __ /_ __ \_ | /| / /
Jul 15 22:41:28 ip-172-31-19-64 bash[31494]: ___ ___ | / _ / _ __/ _ / / /_/ /_ |/ |/ /
Jul 15 22:41:28 ip-172-31-19-64 bash[31494]: _/_/ |_/_/ /_/ /_/ /_/ \____/____/|__/
Jul 15 22:41:28 ip-172-31-19-64 bash[31494]:
Jul 15 22:41:28 ip-172-31-19-64 bash[31494]: [2018-07-15 22:41:28,042] {models.py:189} INFO - Filling up the DagBag from /path/to/my/airflow/home/dags
Jul 15 22:41:28 ip-172-31-19-64 bash[31494]: /home/ubuntu/.local/lib/python3.5/site-packages/flask/exthook.py:71: ExtDeprecationWarning: Importing flask.ext.cache is deprecated, use flask_cach
Jul 15 22:41:28 ip-172-31-19-64 bash[31494]: .format(x=modname), ExtDeprecationWarning
Jul 15 22:41:28 ip-172-31-19-64 bash[31494]: Running the Gunicorn Server with:
Jul 15 22:41:28 ip-172-31-19-64 bash[31494]: Workers: 4 sync
Jul 15 22:41:28 ip-172-31-19-64 bash[31494]: Host: 0.0.0.0:8080
Jul 15 22:41:28 ip-172-31-19-64 bash[31494]: Timeout: 120
Jul 15 22:41:28 ip-172-31-19-64 bash[31494]: Logfiles: - -
Jul 15 22:41:28 ip-172-31-19-64 bash[31494]: =================================================================
Jul 15 22:41:28 ip-172-31-19-64 bash[31494]: Traceback (most recent call last):
Jul 15 22:41:28 ip-172-31-19-64 bash[31494]: File "/usr/local/bin/airflow", line 27, in <module>
Jul 15 22:41:28 ip-172-31-19-64 bash[31494]: args.func(args)
Jul 15 22:41:28 ip-172-31-19-64 bash[31494]: File "/usr/local/lib/python3.5/dist-packages/airflow/bin/cli.py", line 788, in webserver
Jul 15 22:41:28 ip-172-31-19-64 bash[31494]: gunicorn_master_proc = subprocess.Popen(run_args)
Jul 15 22:41:28 ip-172-31-19-64 bash[31494]: File "/usr/lib/python3.5/subprocess.py", line 947, in __init__
Jul 15 22:41:28 ip-172-31-19-64 bash[31494]: restore_signals, start_new_session)
Jul 15 22:41:28 ip-172-31-19-64 bash[31494]: File "/usr/lib/python3.5/subprocess.py", line 1551, in _execute_child
Jul 15 22:41:28 ip-172-31-19-64 bash[31494]: raise child_exception_type(errno_num, err_msg)
Jul 15 22:41:28 ip-172-31-19-64 bash[31494]: FileNotFoundError: [Errno 2] No such file or directory: 'gunicorn'
Jul 15 22:41:28 ip-172-31-19-64 systemd[1]: airflow-webserver.service: Main process exited, code=exited, status=1/FAILURE
Is there some configuration I need to do to make gunicorn compatible with systemd?
Edit:
Following suggestions that this was a permission issue, I installed gunicorn via:sudo apt-get install gunicornand upon re-running the systemctl got the following error Error: No module named airflow.www.gunicorn_config. I figured that this was due to an inconsistency between the gunicorn that I had just installed and the gunicorn my ubuntu user was using to run airflow, so I replaced the gunicorn in /usr/bin/ with the former. This hotfix is likely not the best way to make the fix, but afterwards I was successfully able to run airflow via systemd.

Answer 1

I had the same problem on Ubuntu 18.04 LTS and Apache Airflow version 1.10.1 installed in a virtual environment under /srv/airflow. After lots of trial and errors I ended up with this working solution.
My airflow-webserver.service file:
[Unit]
Description=Airflow webserver daemon
After=network.target
[Service]
Environment="PATH=/srv/airflow/bin"
Environment="AIRFLOW_HOME=/srv/airflow"
User=airflow
Group=airflow
Type=simple
ExecStart=/srv/airflow/bin/airflow webserver --pid /srv/airflow/webserver.pid
Restart=on-failure
RestartSec=5s
PrivateTmp=true
[Install]
WantedBy=multi-user.target
I did this to install the service:
sudo cp airflow-webserver.service /lib/systemd/system/
sudo systemctl daemon-reload
sudo systemctl enable airflow-webserver.service
sudo systemctl start airflow-webserver.service

Answer 2

Yeah, ExecStart=..airflow/bin/airflow requires ..airflow/bin/python but systemd found system python instead. Airflow needs Environment="PATH=..airflow/bin", always.

Answer 3

In Ubuntu Bionic, I found that sudo apt-get install python3-gunicorn first and then sudo apt-get install gunicorn while in the root python environment resolves this problem.