title: Using ccache when building inside of docker
body: <p>I am working on moving the build for a C++ project into a docker image.  The image will be built and pushed by a Jenkins job.  Prior to docker, I made heavy use of ccache to speed up my builds on Jenkins, especially in the case of builds where very little changed.  The trouble with docker is that the build now runs in an isolated environment, so I can no longer benefit from ccache.  Is there a way to build inside of an ephemeral container while still taking advantage of ccache?</p>