Alwaysdata
Context
I have been using the service offered by alwaysdata for more than two years now. I have deployed some ruby on rails apps, and some django apps too. This time, I decided to give a flask application a try. It hasn’t been that easy. For your information, I am far from being proficient with any system administration work, so I got frustrated pretty quickly. The documentation on alwaysdata related to deploying a flask application was almost non-existent. This is why I decided to write this post, which will take you through:
- installation of a custom python (2.7.5)
- installation of setuptools and pip
- installation of virtualenv
- installation of flask and requirements of your app
- creation of your wsgi file
- troubleshooting
Installation of a custom python
jeremydagorn@ssh:~ $ cd
jeremydagorn@ssh:~ $ mkdir python
jeremydagorn@ssh:~ $ cd python
jeremydagorn@ssh:~/python $ mkdir src
jeremydagorn@ssh:~/python $ cd src
Here, we created the folder which will contain our python version that we download by doing the following:
jeremydagorn@ssh:~/python/src $ wget http://www.python.org/ftp/python/2.7.5/Python-2.7.5.tgz
jeremydagorn@ssh:~/python/src $ tar xvfz Python-2.7.5.tgz
jeremydagorn@ssh:~/python/src $ cd Python-2.7.5
We extract the files from the archive and install python:
jeremydagorn@ssh:~/python/src/Python-2.7.5 $ mkdir ~/python/python27
jeremydagorn@ssh:~/python/src/Python-2.7.5 $ ./configure --prefix=~/python/python27
jeremydagorn@ssh:~/python/src/Python-2.7.5 $ make
jeremydagorn@ssh:~/python/src/Python-2.7.5 $ make install
You can of course name python27 whatever you want. Just be careful while following the next steps of the tutorial.
The next step is to make the system recognize the newly installed python as the default one. To do so, just declare it in your .bash_profile.
jeremydagorn@ssh:~/python/src $ echo "export PATH=$HOME/python/python27/bin:$PATH" >> ~/.bash_profile
jeremydagorn@ssh:~/python/src $ source ~/.bash_profile
To verify that your system is using your newly installed python:
jeremydagorn@ssh:~/python/src $ which python
If everything worked as expected, you should see something like this:
jeremydagorn@ssh:/home/jeremydagorn/python/python27/bin/python
Installation of setuptools and pip
Verify that you are still in the src file of your python directory.
jeremydagorn@ssh:~/python/src $ wget https://pypi.python.org/packages/source/s/setuptools/setuptools-1.1.6.tar.gz --no-check-certificate
jeremydagorn@ssh:~/python/src $ tar xvfz setuptools-1.1.6.tar.gz
jeremydagorn@ssh:~/python/src $ cd setuptools-1.1.6
jeremydagorn@ssh:~/python/src/setuptools-1.1.6 $ python setup.py install
jeremydagorn@ssh:~/python/src/setuptools-1.1.6 $ cd ..
jeremydagorn@ssh:~/python/src $ wget https://pypi.python.org/packages/source/p/pip/pip-1.4.tar.gz --no-check-certificate
jeremydagorn@ssh:~/python/src $ tar xvfz pip-1.4.tar.gz
jeremydagorn@ssh:~/python/src $ cd pip-1.4
jeremydagorn@ssh:~/python/src/pip-1.4 $ python setup.py install
Nothing crazy here, we just download, extract the files from the archives and install (as the title says actually).
Installation of virtualenv
Now that pip is installed, installing virtualenv and virtualenvwrapper is really easy.
jeremydagorn@ssh:~ $ pip install virtualenv
jeremydagorn@ssh:~ $ pip install virtualenvwrapper
Now, let’s create a folder which will contain our future virtualenv:
jeremydagorn@ssh:~ $ cd
jeremydagorn@ssh:~ $ mkdir .virtualenvs
jeremydagorn@ssh:~ $ echo ". /home/jeremydagorn/python/python27/bin/virtualenvwrapper.sh" >> .bash_profile
jeremydagorn@ssh:~ $ source .bash_profile
jeremydagorn@ssh:~ $ mkvirtualenv env
Once again, you can specify the name of your virtualenv to match the project using it, so it is easy to identify.
Installation of flask and requirements of your app
Here, I consider the case where you have copied/cloned the repo containing your code to your workspace.
Go into your project repository:
jeremydagorn@ssh:~$ cd www/jeremydagorn-blog/
jeremydagorn@ssh:~/www/jeremydagorn-blog$ ls
authentication.py base.pyc database.py installation.py models.py posts.py README.md static update-virtualenv.sh
authentication.pyc config.pyc forms.py jdblog.db models.pyc posts.pyc requirements.txt templates wtfcustomwidgets.py
base.py config.py.local forms.pyc jdblog.wsgi posts Procfile schema.sql test_base.py wtfcustomwidgets.pyc
If you have a requirements.txt file containing all your requirements and dependencies (or equivalent) simply run:
jeremydagorn@ssh:~ $ pip install -r requirements.txt
This will install all the dependencies using pip. To be able to create this kind of file, just run:
pip freeze > file_which_will_contain_dependencies_name
Creation of your wsgi file
To be able to run your app, you need to create a WSGI file. This file contains the code which is executing on startup to get the application object.
In most of the cases, it should just be able to import your app and will contain something like:
from base import app as application
base.py in my case being the file containing my main method.
You also need to tell this file to start your virtual environment, to get all the different dependencies you use.
You also need to tell this file which python-modules you should use. You can use the method addsitedir() of the module site.
Then, you will have something that looks like the following:
import os
import sys
import site
ALLDIRS = ['/home/jeremydagorn/.virtualenvs/env7/lib/python2.7/site-packages']
# Remember original sys.path.
prev_sys_path = list(sys.path)
# Add each new site-packages directory.
for directory in ALLDIRS:
site.addsitedir(directory)
# Reorder sys.path so new directories at the front.
new_sys_path = []
for item in list(sys.path):
if item not in prev_sys_path:
new_sys_path.append(item)
sys.path.remove(item)
sys.path[:0] = new_sys_path
activate_this = '/home/jeremydagorn/.virtualenvs/env7/bin/activate_this.py'
execfile(activate_this, dict(__file__=activate_this))
sys.path.append(os.path.dirname(__file__))
from base import app as application
application.debug = True
Now, just go to the addresse where your application is supposed to run and check that everything works.
In case something is wrong, first check the apache log.
jeremydagorn@ssh:~$ cd ~/admin/log/
jeremydagorn@ssh:~/admin/log$ ls
2011 2012 2013 2014 access.log error.log
The error should be easy to spot in error.log
Troubleshooting
1. How can I use basic http authentication in production?
Basic http auth is easy to use in flask. Nevertheless, there is an option in Apache not set by default. This option will prevent apache to consume the required headers, meaning that nothing will be sent to your application.
To prevent this just create an .htaccess in your repo and add the following line:
WSGIPassAuthorization On
2. How can I debug if something goes wrong with mod_wsgi configuration?
Check this page and copy/paste the class LoggingMiddleware in your app.wsgi. You will be able to see the request and response sent in your error.log apache file.
3. pip is not able to install my requirement as it does not find anything related to it. How do I install my dependency?
If you get something like the following:
Could not find any downloads that satisfy the requirement <requirement> in /usr/local/lib/python2.7/dist-packages
Some externally hosted files were ignored (use --allow-external spyder to allow).
No distributions at all found for ...
Check your version of pip. If your version is 1.5 or more, it could be related to the fact the pip no longer respects dependency links by default.
You can then either use the --process-dependency-links when installing your dependency, or, what worked for me:
pip install -U --allow-external twill --allow-unverified twill twill
4. How do I use python packages not installed in my virtual environment?
Alwaysdata has some documentation explaining how to install python modules. In my case, it was to install lxml. I installed it using easy_install. If you follow the alwaysdata documentation correctly, it will be as easy as adding a new line there:
ALLDIRS = ['/home/jeremydagorn/.virtualenvs/env7/lib/python2.7/site-packages', "<folder_where_your_package_is_installed"]
Conclusion
I hope this helps. It might not contain enough explanations, or contains wrong formulations. Let me know what you think about this, either on my twitter, or by leaving a comment directly on my github.
A french version of this article is available here.