Currently we port SONiC to buster in a way that building docker-base based on buster and other dockers based on stretch.
The benefit is that tasks can be carried out simultaneously.
The build procedure can be treated as 2 stages.
The first stage is to build the stretch-based debs and dockers and the second stage is to build the buster-based ones.
One thing we have to pay attention to is some debs depend on kernel should not be built at stretch stage because the kernel isn't available at that time.
The idea is to move that kind of debs out of SONIC_STRETCH_DEBS and SONIC_MAKE_DEBS and add them to SONIC_DPKG_DEBS.
Meanwhile, any dependency explicitly put on the stretch based dockers on kernel should be removed.

… --extract

…crng init) which is responsible to random number generation

On some devices the system can take very long to start. Eventually we found it is because crng init takes very long to finish.
Haveged resolves this problem