Production WSGI server

[Starkteetje]

Use a production WSGI server to host the WSGI Connaisseur application. Load and stress testing led us to choose cheroot by a slim margin.

PR also contains some loadtests for the pipeline integration tests

[codecov-commenter]

Codecov Report

Merging #299 (a45aeac) into develop (b91d745) will decrease coverage by 2.74%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           develop     #299      +/-   ##
===========================================
- Coverage    96.99%   94.24%   -2.75%     
===========================================
  Files           21       22       +1     
  Lines         1064     1095      +31     
===========================================
  Hits          1032     1032              
- Misses          32       63      +31     

Impacted Files	Coverage Δ
connaisseur/__main__.py	0.00% <0.00%> (ø)
connaisseur/flask_application.py	91.46% <ø> (ø)
connaisseur/logging_wrapper.py	0.00% <0.00%> (ø)

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[xopham]

wow...awesome review!

This seems to give a tendency towards cheroot which seems a good choice though less known.

However, when checking these out I stumbled across the following blog post: https://fgimian.github.io/blog/2018/05/17/choosing-a-fast-python-api-framework/

In there, it is mentioned that CherryPy (Cheroot) is ruled out bc it was slow, but more importantly that flask was ruled out as a WSGI framework since it was slow and that falcon is apparently blazingly fast and "The no-nonsense REST API and microservices framework for Python developers," which sounds pretty good for our use-case. Now, this will cause some additional effort to test whether the framework makes a significant difference, as that would indeed require some rewriting, but I am wondering whether it makes sense to take a look.
Also, Bjoern is claimed to work for python 2 and 3: https://github.com/jonashaag/bjoern . Apparently, it is a strong choice for containerized environments:

• https://github.com/kubeup/python-wsgi-benchmark
• https://www.appdynamics.com/blog/engineering/a-performance-analysis-of-python-wsgi-servers-part-2/

Beyond that I noticed that uwsgi is supposedly very complex and overloaded.

In summary, it seems cheroot is a decent choice, Bjoern may be better and apparently using Falcon instead of Flask could strongly affect speed, but would require a bit of rewriting...

[Starkteetje]

https://github.com/jonashaag/bjoern/blob/9a6409138c645c47f6fd1d161e84a40daebabb04/bjoern/request.c#L354
bjoern doesnt do TLS though which isnt acceptable for the admission controller afaik

[xopham]

one small version comment, otherwise lgtm!

[annekebr]

Looks very good! Can we delete flask from the requirements?

[Starkteetje]

Looks very good! Can we delete flask from the requirements?

No, since we're still using the flask WSGI application. Just no longer the server. But that's a great point, gotta rename the flask_server file