Re: Call for Interest: Managed SMB Protocol Support

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On Monday, March 25, 2024 3:22:26 PM EDT Alexander E. Patrakov wrote:
> On Mon, Mar 25, 2024 at 11:01 PM John Mulligan
> <phlogistonjohn@xxxxxxxxxxxxx> wrote:
> > On Friday, March 22, 2024 2:56:22 PM EDT Alexander E. Patrakov wrote:
> > > Hi John,
> > > 
> > > > A few major features we have planned include:
> > > > * Standalone servers (internally defined users/groups)
> > > 
> > > No concerns here
> > > 
> > > > * Active Directory Domain Member Servers
> > > 
> > > In the second case, what is the plan regarding UID mapping? Is NFS
> > > coexistence planned, or a concurrent mount of the same directory using
> > > CephFS directly?
> > 
> > In the immediate future the plan is to have a very simple, fairly
> > "opinionated" idmapping scheme based on the autorid backend.
> OK, the docs for clustered SAMBA do mention the autorid backend in
> examples. It's a shame that the manual page does not explicitly list
> it as compatible with clustered setups.
> However, please consider that the majority of Linux distributions
> (tested: CentOS, Fedora, Alt Linux, Ubuntu, OpenSUSE) use "realmd" to
> join AD domains by default (where "default" means a pointy-clicky way
> in a workstation setup), which uses SSSD, and therefore, by this
> opinionated choice of the autorid backend, you create mappings that
> disagree with the supposed majority and the default. This will create
> problems in the future when you do consider NFS coexistence.

Thanks, I'll keep that in mind.

> Well, it's a different topic that most organizations that I have seen
> seem to ignore this default. Maybe those that don't have any problems
> don't have any reason to talk to me? I think that more research is
> needed here on whether RedHat's and GNOME's push of SSSD is something
> not-ready or indeed the de-facto standard setup.

I think it's a bit of a mix, but am not sure either. 

> Even if you don't want to use SSSD, providing an option to provision a
> few domains with idmap rid backend with statically configured ranges
> (as an override to autorid) would be a good step forward, as this can
> be made compatible with the default RedHat setup.

That's reasonable. Thanks for the suggestion.

> > Sharing the same directories over both NFS and SMB at the same time, also
> > known as "multi-protocol", is not planned for now, however we're all aware
> > that there's often a demand for this feature and we're aware of the
> > complexity it brings. I expect we'll work on that at some point but not
> > initially. Similarly, sharing the same directories over a SMB share and
> > directly on a cephfs mount won't be blocked but we won't recommend it.
> OK. Feature request: in the case if there are several CephFS
> filesystems, support configuration of which one to serve.

Putting it on the list.

> > > In fact, I am quite skeptical, because, at least in my experience,
> > > every customer's SAMBA configuration as a domain member is a unique
> > > snowflake, and cephadm would need an ability to specify arbitrary UID
> > > mapping configuration to match what the customer uses elsewhere - and
> > > the match must be precise.
> > 
> > I agree - our initial use case is something along the lines:
> > Users of a Ceph Cluster that have Windows systems, Mac systems, or
> > appliances that are joined to an existing AD
> > but are not currently interoperating with the Ceph cluster.
> > 
> > I expect to add some idpapping configuration and agility down the line,
> > especially supporting some form of rfc2307 idmapping (where unix IDs are
> > stored in AD).
> Yes, for whatever reason, people do this, even though it is cumbersome
> to manage.
> > But those who already have idmapping schemes and samba accessing ceph will
> > probably need to just continue using the existing setups as we don't have
> > an immediate plan for migrating those users.
> > 
> > > Here is what I have seen or was told about:
> > > 
> > > 1. We don't care about interoperability with NFS or CephFS, so we just
> > > let SAMBA invent whatever UIDs and GIDs it needs using the "tdb2"
> > > idmap backend. It's completely OK that workstations get different UIDs
> > > and GIDs, as only SIDs traverse the wire.
> > 
> > This is pretty close to our initial plan but I'm not clear why you'd think
> > that "workstations get different UIDs and GIDs". For all systems acessing
> > the (same) ceph cluster the id mapping should be consistent.
> > You did make me consider multi-cluster use cases with something like
> > cephfs
> > volume mirroring - that's something that I hadn't thought of before *but*
> > using an algorithmic mapping backend like autorid (and testing) I think
> > we're mostly OK there.
> The tdb2 backend (used in my example) is not algorithmic, it is
> allocating. That is, it sequentially allocates IDs on the
> first-seen-first-allocated basis. Yet this is what this customer uses,
> presumably because it is the only backend that explicitly specifies
> clustering operation in its manual page.
> And the "autorid" backend is also not fully algorithmic, it allocates
> ranges to domains on the same sequential basis (see
> 71e7c/source3/winbindd/idmap_autorid_tdb.c#L82), and therefore can create
> mismatching mappings if two workstations or servers have seen the users
> DOMA\usera and DOMB\userb in a different order. It is even mentioned in the
> manual page. SSSD largely avoids this problem by hashing the domain portion
> of the SID instead of
> allocating the subranges on a sequential basis.

Agreed. Thanks for the reminder. This will certainly need to go on the test 

> > > 2. [not seen in the wild, the customer did not actually implement it,
> > > it's a product of internal miscommunication, and I am not sure if it
> > > is valid at all] We don't care about interoperability with CephFS,
> > > and, while we have NFS, security guys would not allow running NFS
> > > non-kerberized. Therefore, no UIDs or GIDs traverse the wire, only
> > > SIDs and names. Therefore, all we need is to allow both SAMBA and NFS
> > > to use shared UID mapping allocated on as-needed basis using the
> > > "tdb2" idmap module, and it doesn't matter that these UIDs and GIDs
> > > are inconsistent with what clients choose.
> > 
> > Unfortunately, I don't really understand this item. Fortunately, you say
> > it
> > was only considered not implemented. :-)
> > 
> > > 3. We don't care about ACLs at all, and don't care about CephFS
> > > interoperability. We set ownership of all new files to root:root 0666
> > > using whatever options are available [well, I would rather use a
> > > dedicated nobody-style uid/gid here]. All we care about is that only
> > > authorized workstations or authorized users can connect to each NFS or
> > > SMB share, and we absolutely don't want them to be able to set custom
> > > ownership or ACLs.
> > 
> > Some times known as the "drop-box" use case I think (not to be confused
> > with the cloud app of a similar name).
> > We could probably implement something like that as an option but I had not
> > considered it before.
> > 
> > > 4. We care about NFS and CephFS file ownership being consistent with
> > > what Windows clients see. We store all UIDs and GIDs in Active
> > > Directory using the rfc2307 schema, and it's mandatory that all
> > > servers (especially SAMBA - thanks to the "ad" idmap backend) respect
> > > that and don't try to invent anything [well, they do - BUILTIN/Users
> > > gets its GID through tdb2]. Oh, and by the way, we have this strangely
> > > low-numbered group that everybody gets wrong unless they set "idmap
> > > config CORP : range = 500-999999".
> > 
> > This is oh so similar to a project I worked on prior to working with Ceph.
> > I think we'll need to do this one eventually but maybe not this year.
> > One nice side-effect of running in containers is that the low-id number is
> > less of an issue because the ids only matter within the container context
> > (and only then if using the kernel file system access methods). We have
> > much more flexibility with IDs in a container.
> So - are you going to use the kernel-based mount or the ceph vfs
> module? My tests indicate that, in situations where there are
> frequently accessed files, allowing the kernel to cache them in RAM
> (which the vfs module does not do) can create a big boost in
> performance. Also, SUSE considers the ceph vfs module a
> non-recommended solution apparently for the same performance-related
> reason, see

The prototype module only uses the vfs module due to the extreme simplicity of 
setting it up in containers. Otherwise, we're trying to keep our options open 
and are investigating multiple approaches currently.

> > > 5. We use a few static ranges for algorithmic ID translation using the
> > > idmap rid backend. Everything works.
> > 
> > See above.
> > 
> > > 6. We use SSSD, which provides consistent IDs everywhere, and for a
> > > few devices which can't use it, we configured compatible idmap rid
> > > ranges for use with winbindd. The only problem is that we like
> > > user-private groups, and only SSSD has support for them (although we
> > > admit it's our fault that we enabled this non-default option).
> > > 7. We store ID mappings in non-AD LDAP and use winbindd with the
> > > "ldap" idmap backend.
> > 
> > For now, we're only planning to do idmapping with winbind and AD. We'd
> > probably only consider non-AD ldap and/or ssd if there was strong and loud
> > demand for it.
> See above.
> However, as I said, providing a way to use the "rid" backend with
> statically defined domains and ranges in addition to the default
> "autorid" backend would be, for me, a good-enough substitute for SSSD.

Sounds reasonable. I've done it that way in a prior role too, so it's somewhat 
familiar.   Thanks!

> > > I am sure other weird but valid setups exist - please extend the list
> > > if you can.
> > > 
> > > Which of the above scenarios would be supportable without resorting to
> > > the old way of installing SAMBA manually alongside the cluster?
> > 
> > I hope I covered the above with some inline replies. This was great food
> > for thought and at just the right level of technical detail. So thank you
> > very much for replying, this is exactly the kind of discussion I want to
> > have now where the design is still young and flexible.
> > 
> > One other cool thing I plan on doing is supporting multiple samba
> > containers running on the same cluster (even the same node if I can
> > wrangle the network properly). So one could in fact have completely
> > different domain joins and/or configurations. While I wouldn't suggest
> > anyone run a whole lot of different configurations on the same cluster -
> > this idea already allows for some level of agility between schemes. Later
> > on we might be able to use that as a building block for migration tools,
> > either from an existing samba setup or between configurations.
> Multiple SAMBA containers are also good for high availability (with
> ctdb) or scale-out (with round-robin DNS).
> > Also, I plan on adding `global_custom_options` and `share_custom_options`
> > for special overrides for development, qa, and experimentation but those
> > are strongly within the "you break it, you bought it" realm. But these
> > could be used for experimenting  with idmapping schemes without having
> > them all baked into the smb mgr module code.
> Great, thanks!

Once again, thanks for the feedback. This discussion is very welcome!

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