E.g. you deploy with DATABASE_URL=x
This becomes DATABASE_URL=x PYTHON=3.0.0
You did not set the Python one, the image did via ENV.
Now a new version comes out with PYTHON=3.1.0.
Watchtower doesn't know which ENVs you set and which ones came from the container as docker inspect exposes them in the same way.
So now Watchtower deploys the new version (which only has Python 3.1.0) with DATABASE_URL=x PYTHON=3.0.0.
And stuff stops working.
I use an ansible playbook which maintains the only ENV vars that need to survive an update.
E.g. you deploy with DATABASE_URL=x
This becomes DATABASE_URL=x PYTHON=3.0.0
You did not set the Python one, the image did via ENV.
Now a new version comes out with PYTHON=3.1.0.
Watchtower doesn't know which ENVs you set and which ones came from the container as docker inspect exposes them in the same way.
So now Watchtower deploys the new version (which only has Python 3.1.0) with DATABASE_URL=x PYTHON=3.0.0.
And stuff stops working.
I use an ansible playbook which maintains the only ENV vars that need to survive an update.