On to, 13 huhti 2017, Simo Sorce wrote:
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.
It would be better to avoid using Kerberos authentication here at all.

Multiple hosts authenticating with the same key would cause a lot of
updates in the LDAP entry representing this principal. This is going to
break replication if this is the only key that is used by multiple hosts
against multiple IPA masters.

--
/ Alexander Bokovoy

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