We are using parcel to perform Continuous Delivery with our buildserver. It works great, but the virtualenv is being created from scratch every time a deployment is triggered. This is a good and clean approach, which, on the other hand, takes a lot of resources and time. Right now, building the virtualenv every time is a bottleneck to the buildout-process. It would come in handy if the virtualenv would simply be cached using it's requirements.txt file as a cache key.