Grocker, a Docker build chain for Python applications

Presenter Notes

Who am I

  • Senior developer at Polyconseil for 2 years
  • Member of the Autolib' [1] dev team
  • Working on DevOps subjects, among others
[1]Paris electric car sharing service

Presenter Notes

  • 6 electric car sharing services
  • Micro services (~30 different apps)
  • Apps based on web technologies, Django and our own libraries (for business logic)

Why we built Grocker

  • Debian packaging was hell (in 2015)
  • Containerized applications are the future!
  • OpenShift/Source-To-Image use source not package [2]
[2]I lied, when we built grocker, we did not know this project

Presenter Notes

  • Debian Packaging
    • Need to update metadata by hand
    • Our worst case: 48h to package one application and all its dependencies
    • Applications are deployed once a week, two days of packaging -> three days for live tests, bug fixes, testing the bug fixes and deployment
    • Setuptools entrypoints do not work (except if all your dependencies are exactly those in your files)
  • Our goal: to deploy all our applications at least once a day
  • Why Docker
    • Build dependencies are not installed on production servers
    • Atomics deployments!
    • Resource optimisation (one host = N Docker)

Other approaches we have considered

  • pip install on server
  • Distribution packages
  • Dockerfile
  • Slug (Heroku like)

Presenter Notes

  • pip install on a production server, seriously?
    • Build extensions in place (ie on production server)
    • Can fail
  • Infrastructure and application dependencies should not be mixed otherwise update of one part can be blocked by the other one.
  • Dockerfile:
    • Extension building: One RUN command to install build dependencies, build wheels, uninstall build dependencies (docker layer, size matters)
  • Slug:
    • Separate build and run phases
    • One base image for all applications
    • No system dependencies (they are on the base image)

How Grocker works

Runner Image dep debian:jessie Root Image Compiler Image Compiler dep App DataVolume Nginx dep dep App 1 2 3 4

Presenter Notes

Build phases:

  1. Build the root image based on debian:jessie (add system packages for runtime dependencies)
  2. Build the compiler image based on the root image (add system packages marked as build dependencies, install compiler script)
  3. Instantiate a container for the compiler image to build Python wheels for the application and its dependencies (and store them in a data volume)
  4. Build the runner image based on the root image (install compiled wheels served by a web server [3])

In fact, this is more complex, there is one root image and one compiler image by "config".

[3]We use the pip --no-index to install wheels.

Why using a compiler image?

  • Wheels, simple and reproducible deployment (see )
  • C extensions need dependencies to compile
  • Docker layers...

Presenter Notes

  • Wheels and C extensions have to be linked with the same library versions than those used at runtime
  • Docker layers: data on layers are never deleted, just masked

Current limitations

  • Root image size: between 200 MB (image used for tests) and 600 MB (for our most cumbersome applications)
    • debian:jessie: 125 MB
    • alpine: 5 MB, but missing zbar
  • Can only build packaged applications

Presenter Notes

How to use it

$ grocker build ipython==5.0 --entrypoint ipython
[wait a long time]
$ docker run --rm -ti ipython:5.0-4.0
Python 3.4.2 (default, Oct  8 2014, 10:45:20)
Type "copyright", "credits" or "license" for more information.

IPython 5.0.0 -- An enhanced Interactive Python.
?         -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help      -> Python's own help system.
object?   -> Details about 'object', use 'object??' for extra details.

In [1]:

Presenter Notes

How to use it (the other side)

With the default configuration, only working for:
  • Packaged applications
  • Python 3
  • Without runtime dependencies

Otherwise, you will need a config file or to use config flags.

Presenter Notes

I need it!

Presenter Notes



Presenter Notes