The Wikimedia Foundation have replaced the varnish backend with Apache Traffic Server. We should have a look at Apache Traffic Server to see if it would benefit us performance wise (and to see if we could get rid of the need for stunnel).
The Wikimedia Foundation still use varnish for the frontend though but we wouldn't do that if we were to switch.
Apache Traffic Server is also proven to be very performant.
Below we have a checklist of things to do before this task is resolved:
 Request a vm T7037
 Deploy vm
 Puppitise a basic apache traffic server module. Basic being a workable module.
Wikimedia have a good module we can reuse https://github.com/wikimedia/puppet/tree/production/modules/trafficserver.
 Security Review (@Southparkfan)
 Performance review. Compare Varnish and ATS performance data.