Troubleshoot TemplateNotFound error from Flask und

Question

I've got a Flask app that I'm trying to deploy using Gunicorn and nginx. However, although it works fine locally, it throws a TemplateNotFound error when I run in with Gunicorn on my remote server.

I'm not sure how to even start debugging this, let alone why it's failing...would love help on the former, if not the latter. I thought maybe it was a permissions issue, so chmod'd the templates folder to 777...no luck. Here's all the relavant details:

install script

Starting with a bare Ubuntu 10.04 install, I run this to set up the server and pull in my code: https://github.com/total-impact/total-impact-deploy/blob/master/deploy.sh. Then I put this nginx config file at /etc/nginx/sites-available/total-impact:

server {
    location / {
        proxy_pass http://127.0.0.1:8000;
    }
}

Finally, I navigate the app directory and run gunicorn web:app, and hit the server's IP address. This generates a 500 in the browser, and this output on the command line:

stack trace:

root@jc:/home/ti/total-impact-webapp/totalimpactwebapp# gunicorn web:app2012-05-28 23:15:06 [15313] [INFO] Starting gunicorn 0.14.3
2012-05-28 23:15:06 [15313] [INFO] Listening at: http://127.0.0.1:8000 (15313)
2012-05-28 23:15:06 [15313] [INFO] Using worker: sync
2012-05-28 23:15:06 [15316] [INFO] Booting worker with pid: 15316
2012-05-28 23:15:12,274 - totalimpactwebapp.core - ERROR - Exception on / [GET]
Traceback (most recent call last):
  File "/usr/local/lib/python2.6/dist-packages/flask/app.py", line 1292, in wsgi_app
    response = self.full_dispatch_request()
  File "/usr/local/lib/python2.6/dist-packages/flask/app.py", line 1062, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/usr/local/lib/python2.6/dist-packages/flask/app.py", line 1060, in full_dispatch_request
    rv = self.dispatch_request()
  File "/usr/local/lib/python2.6/dist-packages/flask/app.py", line 1047, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/home/ti/total-impact-webapp/totalimpactwebapp/web.py", line 60, in home
    return render_template('index.html', commits=False)
  File "/usr/local/lib/python2.6/dist-packages/flask/templating.py", line 120, in render_template
    return _render(ctx.app.jinja_env.get_template(template_name),
  File "/usr/local/lib/python2.6/dist-packages/jinja2/environment.py", line 719, in get_template
    return self._load_template(name, self.make_globals(globals))
  File "/usr/local/lib/python2.6/dist-packages/jinja2/environment.py", line 693, in _load_template
    template = self.loader.load(self, name, globals)
  File "/usr/local/lib/python2.6/dist-packages/jinja2/loaders.py", line 115, in load source, filename, uptodate = self.get_source(environment, name)
  File "/usr/local/lib/python2.6/dist-packages/flask/templating.py", line 61, in get_source
    raise TemplateNotFound(template)
TemplateNotFound: index.html

Answer 1

Today, I experienced identical problems after a long period of my Flask app behaving quite normally (ie not throwing TemplateNotFound exceptions). None of the approaches mentioned by others here hit the mark or seemed appropriate (eg app.debug, path manipulation).

Instead, I tracked it down to the standard Flask app initialisation line:

app = Flask(__name__)

I had changed __name__ to another value (to get access to a named logger), not expecting for all this carnage to unfold :-) Don't change this value unless you are very familiar with Flask internals.

Answer 2

Are your templates in [app root]/templates/?

If so, check to be sure your path is correct. Put this as the first line in the view that handles your homepage:

return app.root_path

If that's what you expect to see - or if you're using Blueprints or another method that changes the default Jinja Environment somehow - it's a little more complicated.

Oddly, Jinja doesn't seem to have a jinja2.Environment.FileSystemLoader.get_search_path() method. I assumed it would have one :(

Answer 3

I have just spent 2 hours in a very similar situation and thought I'd post what ended up being the solution.

I was suddenly getting TemplateNotFound errors in the Apache logs from my Flask application, in production, which had been running fine until then. This resulted in 500 errors across the site.

First issue was that the TemplateNotFound errors did not show unless I had Flask's "debug" flag on -- there was no sign of any problems at all in the Apache log despite LogLevel set to info.

Running the app "locally" (Flask listens on localhost:5000) was fine (one can test the pages via wget 127.0.0.0:5000). It turned out that a copy of the main web app python code had somehow landed in the directory above where it should have been. This was imported by wsgi first and, as a result, the relative path to templates was incorrect.