On Thu, 2017-04-13 at 08:05 -0400, Chris Dagdigian wrote:
> Hi folks,
> 
> I've got a high performance computing (HPC) use case that will need AD 
> integration for user identity management. We've got a working IPA server 
> in AWS that has 1-way trusts going to several remote AD forests and 
> child domains. Works fine but so far all of the enrolled clients are 
> largely static/persistent boxes.
> 
> The issue is that the HPC cluster footprint is going to be elastic by 
> design. We'll likely keep 3-5 nodes in the grid online 24x7 but the vast 
> majority of the compute node fleet (hundreds of nodes quite likely) will 
> be fired up on demand as a mixture of spot, RI and hourly-rate EC2 
> instances. The cluster will automatically shrink in size as well when 
> needed.
> 
> Trying to think of which method I should use for managing users  (mainly 
> UID and GID values) on the compute fleet:
> 
> [Option 1]  Script the enrollment and de-install actions via existing 
> hooks we have for running scripts at "first boot" as well as 
> "pre-termination".  I think this seems technically pretty 
> straightforward but I'm not sure I really need to stuff our IPA server 
> with host information for boxes that are considered anonymous and 
> disposable. We don't care about them really and don't need to implement 
> RBAC controls on them. Also slightly worried that a large-scale 
> enrollment or uninstall action may bog down the server or (worse) 
> perhaps only partially complete leading to an HPC grid where jobs flow 
> into a bad box and die en-mass because "user does not exist..."
> 
> [Option 2]  Steal from the HPC ops playbook and minimize network 
> services that can cause failures. Distribute static files to the worker 
> fleet --  Bind the 24x7 persistent systems to the IPA server and force 
> all HPC users to provide a public SSH key. Then use commands like "id 
> <username" and getent utilities to dump the username/uid/gid values so 
> that we can manufacture static /etc/passwd, /etc/shadow and /etc/group 
> files that can be pushed out to the compute node fleet. The main win 
> here is that we can maintain consistent IPA-derived 
> UID/GID/username/group data cluster wide while totally removing the need 
> for an elastic set of anonymous boxes to be individually enrolled and 
> removed from IPA all the time.
> 
> Right now I'm leaning towards Option #2 but would love to hear 
> experiences regarding moderate-scale automatic enrollment and removal of 
> clients!

One option could also be to keep a (set of) keytab(s) you can copy on
the elastic hosts and preconfigure their sssd daemon. At boot you copy
the keytab in the host and start sssd and everything should magically
work. They all are basically the same identity so using the same key for
all of them may be acceptable.

>From the IPA side it will look like suddenly the same host has multiple
IP addresses and is opening one connection from each of them, but that
is ok.

Simo.

-- 
Simo Sorce
Sr. Principal Software Engineer
Red Hat, Inc


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