Custom SSL handling was introduced because disabling SSL layer compression
provided an approximately five fold performance increase in some
cases. Without SSL layer compression disabled the image transfer would be
CPU bound -- with the CPU performing the DEFLATE algorithm. This would
typically limit image transfers to < 20 MB/s. When --no-ssl-compression
was specified the client would not negotiate any compression algorithm
during the SSL handshake with the server which would remove the CPU
bottleneck and transfers could approach wire speed.
In order to support '--no-ssl-compression' two totally separate code
paths exist depending on whether this is True or False. When SSL
compression is disabled, rather than using the standard 'requests'
library, we enter some custom code based on pyopenssl and httplib in
order to disable compression.
This patch/spec proposes removing the custom code because:
* It is a burden to maintain
Eg adding new code such as keystone session support is more complicated
* It can introduce additional failure modes
We have seen some bugs related to the 'custom' certificate checking
* Newer Operating Systems disable SSL for us.
Eg. While Debian 7 defaulted to compression 'on', Debian 8 has compression
'off'. This makes both servers and client less likely to have compression
enabled.
* Newer combinations of 'requests' and 'python' do this for us
Requests disables compression when backed by a version of python which
supports it (>= 2.7.9). This makes clients more likely to disable
compression out-of-the-box.
* It is (in principle) possible to do this on older versions too
If pyopenssl, ndg-httpsclient and pyasn1 are installed on older
operating system/python combinations, the requests library should
disable SSL compression on the client side.
* Systems that have SSL compression enabled may be vulnerable to the CRIME
(https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2012-4929) attack.
Installations which are security conscious should be running the Glance
server with SSL disabled.
Full Spec: https://review.openstack.org/#/c/187674
Blueprint: remove-custom-client-ssl-handling
Change-Id: I7e7761fc91b0d6da03939374eeedd809534f6edf