If by "hard dependency" you mean something that has to be up strictly
before another thing for a deploy to possibly succeed, I'm not sure if
there are any such hard dependencies. PCFDev (formerly MicroPCF) brings up
all the components simultaneously on a single VM [1
<https://github.com/pivotal-cf/micropcf>]. Some processes will flap until
other ones are up, but they eventually do all come up.

There probably isn't a single solution to minimizing update time while
guaranteeing 100% uptime, as the answer will depend on a lot of different
things. Are you running DEA and/or Diego? External database and/or
external blobstore? Are you just talking about uptime of apps, or also of
the platform API? What about services as well?

If you find a colocation/update strategy that works for you, I think the
community would really appreciate hearing about it.

(Just for fun, there's also nanocf [2 <https://github.com/sclevine/nanocf>]
which is a Docker image with all of CF in it, and a bunch of videos where I
run nanocf in nanocf in BOSH-Lite CF [3
<https://www.youtube.com/watch?v=oMUGjaWg_Hk&list=PLdgSOpBLY_uFbzo1f1prmjW0hf4z1rWdm>
])

[1] https://github.com/pivotal-cf/micropcf
[2] https://github.com/sclevine/nanocf
[3]
https://www.youtube.com/watch?v=oMUGjaWg_Hk&list=PLdgSOpBLY_uFbzo1f1prmjW0hf4z1rWdm

Cheers,
Amit