Remove custom client SSL handling

The Glance client currently supports disabling SSL compression via the –no-ssl-compression argument. This spec proposes deprecating this special handling of SSL.

Note: This is transport layer compression, not application layer (http) compression.

Problem description

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 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.

Proposed change

Deprecate the ‘–no-ssl-compression’ option. Remove the custom http handling code and print a warning when ‘–no-ssl-compression’ is specified.


  • Do not deprecate

The cost/benefit of not deprecating would mean that custom code paths would have to be maintained for a small number of corner cases (that can be addressed by other means).

  • Add dependencies on ndg-httpsclient and pyasn1.

This is a possibility for legacy installations, but this should not be needed for the vast majority of cases.

Data model impact


REST API impact


Security impact

Certificate checking will no longer be done by custom glance client code, but by the ‘requests’ library. I verified that for older python installs (2.7) certificate checking is performed correctly by the requests library.

Systems that have SSL compression enabled may be vulnerable to the CRIME ( attack. Installations which are security conscious should be running the Glance server with SSL disabled.

Notifications impact


Other end user impact

SSL potentially not being disabled. A new deprecation warning.

Performance Impact

If SSL is not disabled user’s will experience a performance hit – until they use one of the alternative methods to disable it.

Other deployer impact

Deprecation warnings. Will need to use an alternative method to disable SSL if appropriate.

Developer impact

Should simplify things.



Stuart McLaren


Ian Cordasco

Work Items

  • Client change

  • (small) nova/cinder changes




There is limited https testing in the gate by default. Some manual functional testing will be done, and devstack will be spun up with https enabled.

Documentation Impact

The cli help will be updated. Any relevant .rst docs will be updated also.


Previous effort: