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Documentation: Basic Concepts of OpenStack are lacking from official Getting Started PDF


Hello all,

Anne: You were recommended contact by Todd Deshane ("deshantm" on IRC)
about this issue.

The problem:
I'm new to OpenStack and while learning it, all of it's concepts seem wild.

I have read the OpenStack Getting Started Guide PDF (from
docs.openstack.org), but it doesn't explain the most basic concepts.

Things like:
1. Why Object Storage (swift) vs. Network File System (NFS)
According to: "notmyname"
<notmyname> technologov: the things that object storage in general
(and swift specifically) provides is large scale, cheap, and durable

<notmyname> technologov: object storage is all about relaxing some of
the constraints of a posix-style system. for example, if you don't
have to provide atomic operations (ie you can rely on eventual
consistency), you can much more easily scale a storage system and not
have a central point of failure

I have seen a video, that explains a bit about hashing searches, but
very incomplete.
Also what happens if new servers get added or removed ?
Such concepts need to be added into the docs.

Does Object Storage also stores files ? (seems yes)

2. Nova vs Images (glance) vs. Object Storage (swift)

Both (1) Nova-volume and (2) glance and (3) swift seem capable of
storing VM hard disks.
What's the conceptual difference between the three ?

Possible Answer:
"<notmyname> technologov: nova-volume is for block storage attached to
a VM. glance is to manage the VM images in a nova cluster and provide
nice ways of storing them (a bridge to the storage, not the storage
itself). swift is an object storage system that can be used by glance
or on its own. swift isn't a filesystem, so it's not "mountable" like
the devices managed with nova-volume"

Arguments & Discussion:
<technologov> come on... "mountable" term is a joke... nowadays you
can mount GMail or Wikipedia... via FUSE
<technologov> w.p. is not a Filesystem either :)

<notmyname> ok, so you don't use swift like a traditional hard drive.
the only access to it is API-based (and the API is http)
<notmyname> that can be wrapped into a FUSE filesystem (but there are
big tradeoffs in doing so--advantages too, of course)

Once we can agree on the concepts, need to patch official docs.

3. Minimal OpenStack setup for new developers to get started is ?
Nova only ? Glance and Swift are optional modules, right?

I'd be glad to help to improve docs, but I don't understand those
concepts myself.

More docs issues:
4. Hierarchies & terminology:
How do you call Live-migration-domain in OpenStack lingo ? (group of
hosts, where virtual machines can be live-migrated from one to the
Are there any other types of domains / virtual machine groups / host
machine groups in OpenStack concept / terminology ?

5. Cross-platform host OS support:
Currently the heavy use of "iptables" mandates Linux host. This
assumption is true if you only support KVM, Xen, LXC, OVZ, UML.
With a possible future port of OpenStack to VirtualBox engine, this
assumption is false.
5.a. Is "iptables" mandatory or optional ?
5.b. What other OpenStack features exist that may fail on FreeBSD
hosts ? And on Windows hosts ?

NOTE: I'm OK if OpenStack effort stays Linux-only, but this must be
clearly documented, along with portability hints.

6. Also Dashboard GUI was not covered in getting started PDF, which
seems important.

7. Security: Remote VM control is secured ? How ? Libvirtd ?
(From my quick look it seems that nova connects to remote
nova-compute, not to libvirtd.)

8. Which other important concepts might I miss ?

-Alexey Eromenko "Technologov", 20.02.2012.

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