Commit c4bb778

title: How to Monitor Python Web Applications

slug: monitor-python-web-applications

meta: Learn how to add monitoring to a Python web application using a hosted monitoring service such as Rollbar.

category: post

date: 2017-09-26

modified: 2017-09-26

headerimage: /img/170926-monitor-python-web-apps/header.jpg

headeralt: Python, Rollbar and Bottle logos, copyright their respective owners.

A quick way to check for errors and issues in your operational

[Python web application](/web-development.html) is to drop-in one of many

awesome hosted [monitoring](/monitoring.html) tools.

Let's learn to quickly add [Rollbar monitoring](https://rollbar.com)

to a web app to visualize when our application is running properly and

when it has issues. This tutorial will use [Bottle](/bottle.html) as the

example [web framework](/web-frameworks.html) along with Rollbar as the

monitoring service but you can also check out the list of other tools

on the [monitoring page](/monitoring.html).

We can use either [Python 2 or 3](/python-2-or-3.html) to build this

tutorial, but Python 3 is *strongly* recommended for all new applications.

[Python 3.6.2](https://www.python.org/downloads/release/python-362/) to

was used to build this tutorial. We will also use the following

[application dependencies](/application-dependencies.html) throughout

the post:

* [pip](https://pip.pypa.io/en/stable/) and

[virtualenv](https://virtualenv.pypa.io/en/latest/), which come installed

with Python 3, to install and isolate the Bottle and Rollbar libraries

from your other projects

* [Bottle](/bottle.html) web framework,

[version 0.12.13](https://bottlepy.org/docs/0.12/)

* [pyrollbar](https://rollbar.com/docs/notifier/pyrollbar/) monitoring

instrumentation library,

[version 0.13.13](https://github.com/rollbar/pyrollbar/tree/v0.13.13)

in Bottle applications so pyrollbar can report on all errors

* A [free Rollbar account](https://rollbar.com/) where we will send error

data and view it when it is captured

If you need help getting your

[development environment](/development-environments.html) configured

before running this code, take a look at

[this guide for setting up Python 3 and Bottle on Ubuntu 16.04 LTS](/blog/python-3-bottle-green-unicorn-ubuntu-1604-xenial-xerus.html).

All code in this blog post is available open source under the MIT license

on GitHub under the

[monitor-python-bottle-apps directory of the blog-code-examples repository](https://github.com/fullstackpython/blog-code-examples).

Use and abuse the source code as you desire for your own applications.

Create a new virtual environment for this project using the following

command. I recommend keeping a separate directory for virtualenvs under

`~/Envs/` so you will know where all your project virtualenvs are located.

python3 -m venv monitorpython

Activate the virtualenv with the `activate` shell script:

source monitorpython/bin/activate

The command prompt will change after activating the virtualenv:

<img src="/img/170926-monitor-python-web-apps/activate-python-virtualenv.png" width="100%" class="technical-diagram img-rounded" style="border:1px solid #ccc" alt="Activating our Python virtual environment on the command line.">

Remember that you need to activate your virtualenv in every new terminal

window where you want to use the virtualenv to run the project.

We can now install Bottle and Rollbar into the activated

virtualenv.

Look for output like the following to confirm the

dependencies installed correctly.

We have our dependencies ready to go so now we can build

our Python web application.

Create a folder for your project named `monitor-python-apps`. `cd` into

the folder and then create a file named `app.py` with the following

code.

import bottle

import os

import re

from bottle import route, template

TEMPLATE_STRING = """

MIN_MSG_LENGTH = 2

@route("/<msg>/")

def show_message(msg):

"""Display a message if the msg value is greater than 2 characters

valid_length = len(msg) >= MIN_MSG_LENGTH

valid_name = re.match('^[a-z\-]+$', msg.lower()) is not None

if valid_length and valid_name:

return template(TEMPLATE_STRING, h1=msg)

else:

error_msg = "Sorry, only alpha characters and hyphens allowed."

raise Exception(error_msg)

if __name__ == "__main__":

bottle.run(host='localhost', port=8080)

The above application code has a few standard Bottle imports so we can

create a Bottle web app and handle URL routes.

We have a single function, `show_message`, that handles a single Bottle

URL route. `show_message` checks if the URL path contains only alphabetic

characters and hyphens for a message to display. If the message passes

the conditions then a page is rendered with that message

in an `h1` element. If `msg` does not pass the condition test then an

exception is thrown that only alpha characters and hyphens are allowed.

Save `app.py` and we can run our code. Execute `app.py` using the `python`

command as follows (make sure your virtualenv is still activated in the

terminal where you are running this command):

python app.py

The Bottle development server should start up and display a few lines

of output.

<img src="/img/170926-monitor-python-web-apps/run-bottle-app.png" width="100%" class="technical-diagram img-rounded" style="border:1px solid #ccc" alt="Run the local Bottle development server.">

What if we try to access the application running on

[localhost port 8080](http://localhost:8080)?

<img src="/img/170926-monitor-python-web-apps/localhost-404.png" width="100%" class="technical-diagram img-rounded" style="border:1px solid #ccc" alt="Testing our Bottle web app at the base URL gets an HTTP 404 error.">

HTTP status 404 page not found, which is what we expected because we only

defined a single route and it did not live at the base path.

Try a URL with a path that contains only alphabetic characters and hyphens,

such as

[localhost:8080/hello-world/](http://localhost:8080/hello-world/).

<img src="/img/170926-monitor-python-web-apps/localhost-hello-world.png" width="100%" class="technical-diagram img-rounded" style="border:1px solid #ccc" alt="Testing at /hello-world/ returns an HTTP 200 response.">

The application was successful in displaying "hello-world" but what if we

try a URL that contains numbers in addition to the alphabetic characters,

such as

[localhost:8080/fullstackpython123/](http://localhost:8080/fullstackpython/)?

<img src="/img/170926-monitor-python-web-apps/localhost-500.png" width="100%" class="technical-diagram img-rounded" style="border:1px solid #ccc" alt="We receive a 500 error when numbers are added to the URL.">

An HTTP 500 error. That is surely not a good user experience.

The 500 error is obvious to us right now because we are

testing the application locally during development. However, what happens

when the app is deployed and a user gets the error in their own web

browser? They will likely quit out of frustration and you will never

know what happened unless you add some error tracking and application

monitoring.

Time to modify our code to add Rollbar to report errors that occur.

Go to the [Rollbar homepage in your browser](https://rollbar.com/)

to add their tool to our Bottle app.

<img src="/img/170926-monitor-python-web-apps/rollbar-homepage.jpg" width="100%" class="technical-diagram img-rounded" style="border:1px solid #ccc" alt="The Rollbar homepage in the Chrome web browser.">

Click the "Sign Up" button in the upper right-hand corner. Enter your

email address, a username and the password you want on the sign up page.

<img src="/img/170926-monitor-python-web-apps/sign-up-page.jpg" width="100%" class="technical-diagram img-rounded" style="border:1px solid #ccc" alt="Enter your account information on the sign up page.">

After the sign up page you will see the onboarding flow where you can

enter a project name and select a programming language. For the project

name type in "Full Stack Python" then select that you are monitoring a

Python app.

<img src="/img/170926-monitor-python-web-apps/create-new-project.jpg" width="100%" class="technical-diagram img-rounded" style="border:1px solid #ccc" alt="Create a new project named 'Battlegrounds' and select Python as the programming language.">

Press the "Continue" button at the bottom to move along. The next

screen shows us a few instructions to add monitoring to a Python

application.

<img src="/img/170723-monitor-flask-apps/project-setup.jpg" width="100%" class="technical-diagram img-rounded" style="border:1px solid #ccc" alt="Set up your project using your server-side access token.">

Let's change our Bottle code to let Rollbar collect and aggregate the

errors that pop up in our application. Modify `app.py` to include the

following highlighted lines.

import bottle

import os

import re

from bottle import route, template

~~from rollbar.contrib.bottle import RollbarBottleReporter

TEMPLATE_STRING = """

MIN_MSG_LENGTH = 2

~~ROLLBAR_SECRET = os.environ.get("ROLLBAR_SECRET")

~~rb_monitor = RollbarBottleReporter(access_token=ROLLBAR_SECRET,

~~ environment='production')

~~bottle.install(rb_monitor)

@route("/<msg>/")

def show_message(msg):

"""Display a message if the msg value is greater than 2 characters

valid_length = len(msg) >= MIN_MSG_LENGTH

valid_name = re.match('^[a-z\-]+$', msg.lower()) is not None

if valid_length and valid_name:

return template(TEMPLATE_STRING, h1=msg)

else:

error_msg = "Sorry, only alpha characters and hyphens allowed."

raise Exception(error_msg)

if __name__ == "__main__":

bottle.run(host='localhost', port=8080)

A new import `from rollbar.contrib.bottle import RollbarBottleReporter`

is our conduit between the application and the Rollbar server. `rollbar`

is the library we installed earlier.

The `ROLLBAR_SECRET` token needs to be set in an environment variable.

Save and quit `app.py`. Run the following command in the terminal where your

virtualenv is activated:

export ROLLBAR_SECRET='token here'

```

If you are uncertain about what your secret token is, it can be found on

the Rollbar onboarding screen.

Note that I typically store all my environment variables in a `.env`

file and use a

[template.env](https://github.com/fullstackpython/blog-code-examples/blob/master/monitor-flask-apps/template.env)

as a template for what I should fill into `.env`. `.env` can be invoked

from the terminal using the `. .env` command. Make sure to *never* commit

your secret tokens to a source control repository though, especially if

the repository is public!

After exporting your `ROLLBAR_SECRET` key as an environment variable

we can test that Rollbar is working as we run our application. Run it

now using `python`:

python app.py

Back in your web browser press the "Done! Go to Dashboard" button.

If an event hasn't been reported yet we'll see a waiting screen like this

one:

<img src="/img/170926-monitor-python-web-apps/waiting.jpg" width="100%" class="technical-diagram img-rounded" style="border:1px solid #ccc" alt="Waiting for data on the Rollbar dashboard.">

Make sure your Bottle development server is running and try to go to

[localhost:8080/fullstackpython123/](http://localhost:8080/fullstackpython123/).

A 500 server error is immediately reported on the dashboard:

<img src="/img/170926-monitor-python-web-apps/exception-reported.jpg" width="100%" class="technical-diagram img-rounded" style="border:1px solid #ccc" alt="Viewing the 500 errors reported in the Rollbar dashboard.">

We even get an email with the error (which can also be turned off if you

don't want emails for every error):

<img src="/img/170926-monitor-python-web-apps/email-error-report.jpg" width="100%" class="technical-diagram img-rounded" style="border:1px solid #ccc" alt="Email with the Rollbar error report.">

Nice, with just a few lines of code we now have our Bottle app reporting

errors for any user that's working with our application.

We just learned how to catch and handle errors with Rollbar as a hosted

monitoring platform in a simple example

[Bottle application](/bottle.html). Next you will want to

add [monitoring](/monitoring.html) to more complicated web apps, including

ones that use [Django](/django.html) or [Flask](/flask.html). You can also

try Rollbar's more advanced features to:

* [set up rules to group errors](https://rollbar.com/docs/custom-grouping/)

* [debug and track deployment issues](https://rollbar.com/docs/deploy-tracking/)

* [sort and view errors by user](https://rollbar.com/docs/person-tracking/)

There is plenty more to learn about in the areas of

[web development](/web-development.html) and

[deployments](/deployments.html) so keep learning by reading

about [web frameworks](/web-frameworks.html). You can also learn more

about integrating Rollbar with Python applications via

[their Python documentation](https://rollbar.com/docs/notifier/pyrollbar/).

Questions? Let me know via

[a GitHub issue ticket on the Full Stack Python repository](https://github.com/mattmakai/fullstackpython.com/issues),

on Twitter

or [@mattmakai](https://twitter.com/mattmakai).

Do you see a typo, syntax issue or just something that's confusing in this

blog post? Fork

[this page's source on GitHub](https://github.com/mattmakai/fullstackpython.com/blob/master/content/posts/170926-monitor-python-web-apps.markdown)

and submit a pull request with a fix or

[file an issue ticket on GitHub](https://github.com/mattmakai/fullstackpython.com/issues).