Simple flask app on heroku – all steps (almost)

Note – instructions assume Ubuntu Linux.

See Getting Started with Python on Heroku (Flask) for the official instructions. The instructions below tackle things differently and include redis-specific steps.

Don’t need postgresql for my app even though needed for heroku demo app. Using redis for simple key-value store.

Main reason for each step is indicated in bold at start. There are lots of steps but there are lots of things being achieved. And each purpose only requires a few steps so probably hard to streamline any further.

  1. APP & BEST PRACTICE
    >> sudo apt-get install python3 python3-pip python-virtualenv git ruby redis-server redis-tools
  2. HEROKU
    Get free heroku account
  3. HEROKU
    Install heroku toolbelt Heroku setup. Sets up virtualenvwrapper for you too (one less thing to figure out)
  4. HEROKU
    Do the once-ever authentication
    >> heroku login
  5. APP
    Make project folder e.g.
    >> mkdir ~/projects/myproj
  6. APP
    >> cd ~/projects/myproj
  7. HEROKU
    >> echo “web: python main.py” > Procfile
  8. HEROKU & BEST PRACTICE
    >> git init
  9. HEROKU & BEST PRACTICE
    >> mkvirtualenv sticky

    So requirements for specific project can be separated from other project – lets heroku identify actual requirements. Normally “workon sticky” thereafter; deactivate to exit virtual env

  10. APP
    >> pip3 install flask
    Note – installed within virtualenv
  11. HEROKU
    Save the following as requirements.txt – needed by heroku so it knows the dependencies. Update version of redis as appropriate. gunicorn is a better approach than the flask test server
    flask
    gunicorn
    redis==2.10.3
  12. HEROKU
    So we can use Python 3.4 instead of the current default of 2.7:
    >> echo “python-3.4.3″ > runtime.txt
  13. APP & HEROKU

    Make a toy app to get started from.

    Note – modify the standard demo flask app to add a port to ease eventual heroku deployment. Otherwise the app will fail because of a problem with the port when running

    heroku ps:scale web=1

    Starting process with command `python main.py`
    ...
    Web process failed to bind to $PORT within 60 seconds of launch

    Here is an example (may need updating if flask changes):

    import os
    from flask import Flask
    app = Flask(__name__)

    @app.route("/")
    def hello():
        return "Hello World!"

    if __name__ == "__main__":
        port = int(os.environ.get("PORT", 33507))
        app.run(host='0.0.0.0', port=port)

  14. BEST PRACTICE
    >> deactivate
  15. Make a module to make it easier to work with redis – let’s call it store.py:

    import os
    import urllib
    import redis

    url = urllib.parse.urlparse(os.environ.get('REDISTOGO_URL',
        'redis://localhost:6379'))
    redis = redis.Redis(host=url.hostname, port=url.port, db=0,
        password=url.password)

    We can then use redis like this:
    from store import redis

  16. APP
    Keep building app locally. The following is good for redis: Redis docs. And flasks docs are always good: Flask Docs – Minimal Application
  17. HEROKU & BEST PRACTICE

    Before deploying to production:

    1. Update git otherwise you’ll be deploying old code – heroku uses git for deployment
    2. set app.debug to False (although no rush when just getting started and not expecting the app to get hit much)
    3. probably switch to gunicorn sooner or later (will need to change ProcFile to
      web: gunicorn main:app --workers $WEB_CONCURRENCY
      )
    4. Example nginx.conf:

      # As long as /etc/nginx/sites-enable/ points to
      # this conf file nginx can use it to work with
      # the server_name defined (the name of the file
      # doesn't matter - only the server_name setting)
      # sudo ln -s /home/vagrant/src/nginx.conf ...
      #     ... /etc/nginx/sites-enabled/myproj.com
      # Confirm this link is correct
      # e.g. less /etc/nginx/sites-enabled/myproj.com

      server {
          listen 80;
          server_name localhost;

          location /static { # static content is

              # handled directly by NGINX which means
              # the nginx user (www-data) will need
              # read permissions to this folder
              root /home/vagrant/src;

          }

          location / { # all else passed to Gunicorn to handle
              # Pass to wherever I bind Gunicorn to serve to
              # Only gunicorn needs rights to read, write,
              # and execute scripts in the app folders
              proxy_pass http://127.0.0.1:8888;
          }
      }

    5. Example gunicorn.conf
      import multiprocessing

      bind = "127.0.0.1:8888" # ensure nginx passes to this port
      logfile = "/home/vagrant/gunicorn.log"
      workers = multiprocessing.cpu_count() * 2 + 1

  18. HEROKU
    >> heroku create

    Should now be able to browse to the url supplied as stdout fom command e.g.
    https://not-real-1234.herokuapp.com/. Note – not working yet – still need to deploy to new app

    >> git push heroku master

    Must then actually spin up the app:

    >> heroku ps:scale web=1

    A shortcut for opening is

    >> heroku open

  19. HEROKU
    Add redis support (after first deployment – otherwise

    ! No app specified.
    ! Run this command from an app folder or specify which app to use with --app APP.
    )
    >> heroku addons:create redistogo

    Note – need to register credit card to use any add-ons, even if free ones. Go to https://heroku.com/verify

Some other points: when developing on a different machine, I needed to supply my public key to heroku from that other machine (Permission denied (publickey) when deploying heroku code. fatal: The remote end hung up unexpectedly).

heroku keys:add ~/.ssh/id_rsa.pub

And the full sequence for upgrading your app after the prerequisites have been fulfilled is:

  1. git commit to local repo
  2. Then git push to heroku
  3. Then run heroku ps:scale web=1 again

And I had a problem when I switched from Python 2 to 3 with redis – my heroku push wouldn’t work. By looking at the logs (>> heroku logs –tail) I found that import imap wouldn’t work and searching on that generally found I needed a newer version of redis than I had specified foolishly in requirements.txt.

F-spot vanished in Ubuntu 15.04 (Vivid)

F-spot has been removed from Ubuntu Vivid (15.04).

http://www.ubuntuupdates.org/package/core/utopic/universe/base/f-spot

Dependency is not satisfiable: liblcms1 (>= 1.15-1)

None of the data for f-spot was gone, just the ability to run the application – probably something to do with mono library deprecation.

~$ find / -name f-spot 2>/dev/null
/home/g/.gconf/apps/f-spot
/home/g/.config/f-spot

1.3MB in /home/g/.config/f-spot/photos.db

Anyway, opened Shotwell, “Import from Application”, “Import media from: F-Spot”, moving on.

Printer driver for Canon MG-7100 on Ubuntu

Once again I was solving a computer problem for my parents-in-law ;-). This time, it was yet another new printer they had bought – a Canon MG7100. Usually, I have had a really good experience with modern Ubuntu and popular printers. They Just Work. And this time it seemed things had gone well again. And they almost had. Except the colours were a bit off. On the Ubuntu printer test page Magenta was brown, bright green was instead a darker green, and yellow was very muddy – more like taupe. I wasted a lot of time cleaning ink nozzles etc etc but the actual solution was to choose a slightly different driver manually from the Canon list. There were two v4.0 options and it was the second that worked.

Category Good setting Bad setting
Job ID Canon-MG7100-2-671 Canon-MG7100-665
Driver CNMG7100.PPD STP00541.PPD
Driver Version 1.0 5.2.10-pre2
Description Canon MG7100 Canon MG7100
Driver Version Canon MG7100 Canon MG7100
Make and Model Canon MG7100 series Ver.4.00 Canon MG7100 series – CUPS+Gutenprint v5.2.10
Printer Canon-MG7100-2 Canon-MG7100

Hope this helps someone else.

Listing Python scripts changed most recently

find / -name *.py -type f -mtime -60 -printf '%TY-%Tm-%Td %TT %p\n' 2>/dev/null | sort -r

Command/options Explanation
find Not as fast as locate but has many advantages. See locate vs find: usage, pros and cons of each other
-name *.py Only find python scripts
-mtime -60 -mtime is days
-printf ‘%TY-%Tm-%Td %TT %p\n’ Displays output with easy-to-read dates
2>/dev/null Pumps all the annoying output about lacking permissions into /dev/null i.e. ignores them
| Pipes output through to be sorted
sort -r Sort so most recent are at top

Also see
How to find recently modified files on Linux

Complex good – complicated bad

In the Zen of Python we are taught that complex is better than complicated. Which is fair enough if we understand the terms as follows:

It is ok if something is complex so long as it is not complicated.

complex: composed of many interconnected parts; compound; composite

complicated: difficult to analyze or understand

Complex vs Complicated

Any decent web framework is going to be a bit complex becauise of all the moving parts it has to handle. But it should make sense and be logically structured enough to avoid being overly complicated.

Eclipse and PyDev on Utopic

I upgraded to Utopic (Utopic Unicorn a.k.a 14.10) and eclipse wouldn’t complete loading anymore. Solution:

Download latest plain vanilla Eclipse from the standard downloads page. And feel free to donate something too.

sudo su

chown -R root:root /home/username/eclipse && mv /home/username/Downloads/eclipse /opt

ln -s /opt/eclipse/eclipse /usr/local/bin/eclipse && exit

Start by running:

eclipse

It didn’t even break PyDev so my luck’s finally turning ;-).

https://www.tumblr.com/search/install+eclipse+ubuntu

Testing new Ubuntu versions

Newer Ubuntu versions are less dramatically new these days, which is probably a good thing, but I like to take them for a spin anyway – old habits and all that. One nice change since the days of Dapper Drake is the ability to boot off a usb stick – much easier than having to burn CDs. On my laptop, I get to the boot menu by pressing the Esc key soon after booting and then selecting the USB stick to boot off. But there can still be problems. In particular, I was receiving the error message:

gfxboot.c32: not a COM32R image

Turns out you need to press the tab key and then type in “live”. Obvious really (not) Ubuntu 14.04 LTS live USB boot error (gfxboot.c32:not a valid COM32R imag).

Another good thing about modern Ubuntus is that they generally work out of the box just how I like them. I remove items from the launcher, shrink the icon size and add the Show Desktop icon to the launcher (under System Settings > Appearance), and I’m almost good to go. There is still one thing that takes a bit of fiddling – adding the ability to minimise on click (Ubuntu 14.04 Adds ‘Click to Minimize App’ Option to Unity Launcher).

Step 1: Open Ubuntu Software Centre
Step 2: Install CompizConfig Settings Manager
Step 3: Open Ubuntu Unity plugin
Step 4: Launcher > Minimize Single Window Applications (Unsupported)

On the one hand the version changes aren’t as exciting as they used to be, but on the other, it’s never been easier to check them out.

Deploying simple flask app on heroku

I’m now a fan of Heroku. How cool is it to be able to deploy a Python app to free hosting?!

Blackbox flask app on Heroku

But in spite of great docs at Getting Started with Python on Heroku there were a few issues I had to handle. The main problems were because the instructions assumed you wanted to start with their demo app and not your own – which meant that they only explained things like requirements.txt and Procfile after you needed to have already made them (they were already present in the demo version).

Note – I am already familiar with git so I don’t explain that here – see Starting a simple Flask app with Heroku for more fleshed-out instructions.

Anyway, here is what I needed to do at the start:

1) Change the app.run(host='0.0.0.0') line to
port = int(os.environ.get("PORT", 33507))
app.run(host='0.0.0.0', port=port)

Otherwise the app would fail because of a problem with the port when I ran

heroku ps:scale web=1

Starting process with command `python main.py`
...
Web process failed to bind to $PORT within 60 seconds of launch

2) I really needed to use virtualenvwrapper and create a requirements.txt file e.g.

cd <folder with code in it>
mkvirtualenv blackbox

Otherwise heroku wouldn’t know what dependencies my app needed fulfilled to work successfully.

To update requirements.txt after changes,

cd <folder with code in it>
workon blackbox
pip freeze > requirements.txt
deactivate blackbox

3) I needed to make a Procfile:

web: python main.py

Note, this was a toy flask app so not using gunicorn etc. Probably should look into that later:

4) Setting debug mode off probably isn’t essential for deployment but probably a good idea anyway: app.debug = False before deploying.

Some other points: when developing on a different machine, I needed to supply my public key to heroku from that other machine (Permission denied (publickey) when deploying heroku code. fatal: The remote end hung up unexpectedly).

heroku keys:add ~/.ssh/id_rsa.pub

And the full sequence for upgrading your app after the prerequisites have been fulfilled is:

  1. Make sure you have the port set for heroku
  2. Then git to local repo
  3. Then git push to heroku
  4. Then run heroku ps:scale web=1 again
  5. Revert from the heroku port back to local for local testing and dev.

heroku addons:add redistogo

To add redis support – NB need to register credit card to use any add-ons, even if free ones.

IDLE3 as default for py files on Ubuntu

Yes – I know, there are better alternatives to IDLE out there, but I am used to it for quick and dirty changes to python files (I use eclipse + pydev for more serious work). And I am increasingly making the switch to Python 3. So when I double click on a py file, odds are I want to open it with IDLE for Python 3 not Python 2.

Start by making sure you have a desktop file like the following:

gksudo gedit /usr/share/applications/idle-python3.4.desktop

[Desktop Entry]
Name=IDLE (using Python-3.4)
Comment=Integrated Development Environment for Python (using Python-3.4)
Exec=/usr/bin/idle-python3.4
Icon=/usr/share/pixmaps/python3.4.xpm
Terminal=false
Type=Application
Categories=Application;Development;
StartupNotify=true

Then make the desktop entry the default for python files:

gedit ~/.local/share/application/mimeapps.list

[Default Applications]
text/w-python=idle-python3.4.desktop

Note – no trailing semi-colon.

And in Linux Mint:

Linux Mint:

ls /usr/share/applications/

identify appropriate .desktop file

gedit /usr/share/applications/defaults.list

add the appropriate .desktop file reference at the front of the python line as appropriate.