The following set of steps should leave you with a Docker container that is relatively small, built from your local checked out source, and even provides you with a nice little RPM too!
Build the package container image. This uses FPM so no
spec files and
such are necessary.
docker build --pull -f contrib/docker/Dockerfile.packager -t asterisk-build .
Build the Asterisk RPM from the resulting container image.
docker run -ti \ -v $(pwd):/application:ro \ -v $(pwd)/out:/build \ -w /application asterisk-build \ /application/contrib/docker/make-package.sh 13.6.0
NOTE: If you need to build this on a system that has SElinux enabled you'll need to use the following command instead:
docker run -ti \ -v $(pwd):/application:Z \ -v $(pwd)/out:/build:Z \ -w /application asterisk-build \ /application/contrib/docker/make-package.sh 13.6.0
Now create your own Asterisk container image from the resulting RPM.
docker build --rm -t madsen/asterisk:13.6.0-1 -f contrib/docker/Dockerfile.asterisk .