SCS Flavor Naming Standard
Introduction
This is the standard v1.0 for SCS Release 0. Note that we intend to only extend it (so it's always backwards compatible), but try to avoid changing in incompatible ways.
Motivation
In OpenStack environments there is a need to define different flavors for instances. The flavors are pre-defined by the operator, the customer can not change these. OpenStack providers thus typically offer a large selection of flavors.
While flavors can be discovered (openstack flavor list), it is helpful for users (DevOps teams),
to have
- A naming scheme that is used across all SCS flavors, so flavor names have the same meaning everywhere.
- Have a guaranteed set of flavors available on all SCS clouds, so these do not need to be discovered.
While not all details will be encoded in the name, the key features should be obvious: Number of vCPUs, RAM, Root Disk. Extra features are important as well: There will be flavors with GPU support, fast disks for databases, memory-heavy applications, and other useful aspects of an instance.
It may also be important to make the CPU generation clearly recognisable, as this is always a topic in discussions with customers.
Proposal
Type of information included
We believe the following characteristics are important in a flavour description:
| Type | Description |
|---|---|
| Generation | CPU Generation |
| Number of CPU | Number of vCPUs - suffixed by L,V,T,C (see below) |
| Amount of RAM | Amount of memory available for the VM |
| Performance Class | Ability to label high-performance CPUs, disks, network |
| CPU Type | X86-intel, X86-amd, ARM, RISC-V, Generic |
| "bms" | Bare Metal System (no virtualization/hypervisor) |
Complete Proposal
| Prefix | CPU | Suffix | RAM[GiB] | optional: Disk[GB] | optional: Disk type | optional: extra features |
|---|---|---|---|---|---|---|
SCS- | N | L/V/T/C[i] | :N[u][o] | [:[Mx]N] | [n/s/l/p] | [-hyp][-hwv]-[arch[N][h][-[G/g]X[N][:M[h]]][-ib] |
(Note that N and M are placeholders for numbers here).
Proposal Details
[REQUIRED] CPU Suffixes
| Suffix | Meaning |
|---|---|
| C | dedicated Core |
| T | dedicated Thread (SMT) |
| V | vCPU (oversubscribed) |
| L | vCPU (heavily oversubscribed) |
Baseline
Note that vCPU oversubscription for a V vCPU should be implemented such, that we
can guarantee at least 20% of a core in >99% of the time; this can be achieved by
limiting vCPU oversubscription to 5x per core (or 3x per thread when SMT/HT is enabled)
or by more advanced workload management logic. Otherwise L (low performance) must be
used. The >99% is measured over a month (1% is 7.2h/month).
Note that CPUs must use latest microcode to protect against CPU vulnerabilities (Spectre, Meltdown, L1TF, etc.).
We expect that microcode gets updated within less than a month of a new release; for CVSS scores above 8,
we expect less than a week.
The provider must enable at least all mitigations that are enabled by default in the Linux kernel. CPUs that
are susceptible to L1TF (intel x86 pre Cascade Lake) must switch off hyperthreading OR (in the future)
use core scheduling implementations that are deemed to be secure by the SCS security team, or declare themselves
as insecure with the i suffix (see below).
Higher oversubscription
Must be indicated with a L vCPU type (low performance for > 5x/core or > 3x/thread oversubscription and
the lack of workload management that would prevent worst case performance < 20% in more than 7.2h per month).
Insufficient microcode
Not using these mitigations must be indicated by an additional i suffix for insecure
(weak protection against CPU vulns through insufficient microcode, lack of disabled hyperthreading
on L1TF susceptible CPUs w/o effective core scheduling or disabled protections on the host/hypervisor).
Examples
- SCS-2C:4:10n
- SCS-2T:4:10n
- SCS-2V:4:10n
- SCS-2L:4:10n
- SCS-2Li:4:10n
SCS-2:**4:10n- CPU suffix missingSCS-2iT:4:10n- This order is forbidden
[REQUIRED] Memory
Baseline
We expect cloud providers to use ECC memory. Memory oversubscription is not recommended. It is allowed to specify half GiBs (e.g. 3.5), though this is discouraged for larger memory sizes (>= 10GiB).
No ECC
If no ECC is used, the u suffix must indicate this.
Enabled Oversubscription
You have to expose this with the o sufffix.
Examples
- SCS-2C:4:10n
- SCS-2C:3.5:10n
- SCS-2C:4u:10n
- SCS-2C:4o:10n
- SCS-2C:4uo:10n
SCS-2C:4ou:10n- This order is forbidden
[OPTIONAL] Disk sizes and types
| Disk type | Meaning |
|---|---|
| n | Network shared storage (ceph/cinder) |
| h | Local disk (HDD: SATA/SAS class) |
| s | Local SSD disk |
| p | Local high-perf NVMe |
Baseline
Note that disk type might be omitted — the user then can not take any assumptions on what storage is provided for the root disk (that the image gets provisioned to).
It does make sense for n to be requested explicitly to allow for smooth live migration.
h typically provides latency advantages vs n (but not necessarily bandwidth and
also is more likely to fail), s and p are for applications that need low
latency (high IOPS) and bandwidth disk I/O. n storage is expected to survive
single-disk and single-node failure.
If the disk size is left out, the cloud is expected to allocate a disk (network or local)
that is large enough to fit the root file system (min_disk in image). This automatic
allocation is indicated with : without a disk size.
If the : is left out completely, the user must create a boot volume manually and
tell the instance to boot from it or use the
block_device_mapping_v2
mechanism explicitly to create the boot volume from an image.
Multi-provisioned Disk
The disk size can be prefixed with Mx prefix, where M is an integer specifying that the disk
is provisioned M times.
Examples
- SCS-2C:4:10n
- SCS-2C:4:10s
- SCS-2C:4:10s-bms-z3
- SCS-2C:4:3x10s - Cloud creates three 10GB SSDs
- SCS-2C:4:3x10s-bms-z3
- SCS-2C:4:10 - Cloud decides disk type
- SCS-2C:4:10-bms-z3
- SCS-2C:4:n - Cloud decides disk size (min_disk from image or larger)
- SCS-2C:4:n-bms-3
- SCS-2C:4: - Cloud decides disk type and size
- SCS-2C:4:-bms-z3
- SCS-2C:4:-bms-z3h-GNa:64-ib
- SCS-2C:4:-ib
- SCS-2C:4 - You need to specify a boot volume yourself (boot from volume, or use block_device_mapping_v2)
- SCS-2C:4-bms-z3
- SCS-2C:4:3x - Cloud decides disk type and size and creates three of them (FIXME: Is this useful?)
- SCS-2C:4:3xs - Cloud decides size and creates three local SSD volumes (FIXME: useful?)
- SCS-2C:4:3x10 - Cloud decides type and creates three 10GB volumes
SCS-2C:4:1.5n- You must not specify disk sizes which are not in full GiBs
[OPTIONAL] Hypervisor
The default Hypervisor is assumed to be KVM. Clouds, that offer different hypervisors
or Bare Metal Systems should indicate the Hypervisor according to the following table:
| hyp | Meaning |
|---|---|
| kvm | KVM |
| xen | Xen |
| vmw | VMware |
| hyv | Hyper-V |
| bms | Bare Metal System |
Examples
- SCS-2C:4:10n
- SCS-2C:4:10n-bms
- SCS-2C:4:10n-bms-z3h
[OPTIONAL] Hardware virtualization / Nested virtualization
If the instances that are created with this flavor support hardware-accelerated
virtualization, this can be reflected with the -hwv flag (after the optional
Hypervisor flag). On x86, this means that in the instance, the CPU flag vmx (intel)
or svm (AMD) is available. This will be the case on Bare Metal flavors on almost
all non-ancient x86 CPUs or if your virtualization hypervisor is configured to
support nested virtualization.
Flavors without the -hwv flag may or may not support hardware virtualization (as we
recommend enabling nesting, but don't require flavor names to reflect all
capabilities. Flavors may overdeliver ...)
Examples
- SCS-2C:4:10 - may or may not support HW virtualization in VMs
- SCS-2C:4:10-kvm-hwv
- SCS-2C:4:10-hwv - not recommended, but allowed
SCS-2C:4:10-hwv-xen- illegal, wrong ordering
[OPTIONAL] CPU Architecture Details
Arch details provide more details on the specific CPU:
- Vendor
- Generation
- Frequency
Generation and Vendor
The generations are vendor specific and can be left out. Not specifying arch means that we have a generic CPU (x86-64).
| Generation | i (Intel x86-64) | z (AMD x86-64) | a (AArch64) | r (RISC-V) |
|---|---|---|---|---|
| 0 | pre Skylake | pre Zen | pre Cortex A76 | TBD |
| 1 | Skylake | Zen-1 (Naples) | A76/NeoN1 class | TBD |
| 2 | Cascade Lake | Zen-2 (Rome) | A78/x1/NeoV1 class | TBD |
| 3 | Ice Lake | Zen-3 (Milan) | A71x/NeoN2 (ARMv9) | TBD |
| 4 | Zen-4 (Genoa) | TBD |
It is recommended to leave out the 0 when specifying the old generation; this will
help the parser tool, which assumes 0 for an unspecified value and does leave it
out when generating the name for comparison. In other words: 0 has a meaning of
"rather old or unspecified".
Frequency Suffixes
| Suffix | Meaning |
|---|---|
| h | >2.75GHz all-core |
| hh | >3.25GHz all-core |
| hhh | >3.75GHz all-core |
Examples
- SCS-2C:4:10n
- SCS-2C:4:10n-z
- SCS-2C:4:10n-z3
- SCS-2C:4:10n-z3h
- SCS-2C:4:10n-z3hh
- SCS-2C:4:10n-bms-z
- SCS-2C:4:10n-bms-z3
- SCS-2C:4:10n-bms-z3
- SCS-2C:4:10n-bms-z3h
- SCS-2C:4:10n-bms-z3hh
[OPTIONAL] Extra features
Note that these are optional — it is recommended for providers to encode this information
into the flavor name, so there is a systematic way of differentiating flavors.
Providers could leave it out however, leaving it to extra_specs to make these flavor
capabilities discoverable. Nothing prevents providers from registering the same flavor
under a secondary (or tertiary) name.
-GX[N][:M[h]] indicates a Pass-Through GPU from vendor X of gen N with M compute units / SMs / EUs exposed.
-gX[N][:M[h]] indicates a vGPU from vendor X of gen N with M compute units / SMs / EUs assigned.
Note that the vendor letter is mandatory, generation and compute units are optional.
| GPU | Vendor |
|---|---|
| N | nVidia |
| A | AMD |
| I | Intel |
Generations could be nVidia (f=Fermi, k=Kepler, m=Maxwell, p=Pascal, v=Volta, t=turing, a=Ampere, ...), AMD (GCN-x=0.x, RDNA1=1, RDNA2=2), intel (Gen9=0.9, Xe(12.1)=1, ...), ... (Note: This may need further work to properly reflect what's out there.)
The optional h suffix to the comput unit count indicates high-performance (e.g. high freq or special
high bandwidth gfx memory such as HBM);
h can be duplicated for even higher performance.
-ib indicates Inifinband networking.
More extensions will be forthcoming.
Extensions need to be specified in the above mentioned order.
Proposal Examples
| Example | Decoding |
|---|---|
| SCS-2C:4:10n | 2 dedicated cores (x86-64), 4GiB RAM, 10GB network disk |
| SCS-8Ti:32:50p-i1 | 8 dedicated hyperthreads (insecure), Skylake, 32GiB RAM, 50GB local NVMe |
| SCS-1L:1u:5 | 1 vCPU (heavily oversubscribed), 1GiB Ram (no ECC), 5GB disk (unspecific) |
| SCS-16T:64:200s-GNa:64-ib | 16 dedicated threads, 64GiB RAM, 200GB local SSD, Inifiniband, 64 Passthrough nVidia Ampere SMs |
| SCS-4C:16:2x200p-a1 | 4 dedicated Arm64 cores (A78 class), 16GiB RAM, 2x200GB local NVMe drives |
| SCS-1V:0.5 | 1 vCPU, 0.5GiB RAM, no disk (boot from cinder volume) |
Standard SCS flavors
These are flavors expected to exist on standard SCS clouds (x86-64).
We expect disk sizes to be 5, 10, 20, 50, 100, 200, 500, 1000GB, 2000GB. We expect a typical CPU
| vCPU:RAM ratio | Mandatory Flavors |
|---|---|
| 1:4 | SCS-1V:4, SCS-1V:4:10 |
| 2:8 | SCS-2V:8, SCS-2V:8:20 |
| 4:16 | SCS-4V:16, SCS-4V:16:50 |
| 8:32 | SCS-8V:32, SCS-8V:32:100 |
| 1:2 | SCS-1V:2, SCS-1V:2:5 |
| 2:4 | SCS-2V:4, SCS-2V:4:10 |
| 4:8 | SCS-4V:8, SCS-4V:8:20 |
| 8:16 | SCS-8V:16, SCS-8V:16:50 |
| 16:32 | SCS-16V:32, SCS-16V:32:100 |
| 1:8 | SCS-1V:8, SCS-1V:8:20 |
| 2:16 | SCS-2V:16, SCS-2V:16:50 |
| 4:32 | SCS-4V:32, SCS-4V:32:100 |
| 1:1 | SCS-1L:1, SCS-1L:1:5 |
Note that all vCPUs are oversubscribed — the smallest 1L:1 flavor allows
for heavy oversubscription (note the L), and thus can be offered very
cheaply — imagine jump hosts ...
Disks types are not specified (and expected to be n or h typically).
The design allows for small clouds (with CPUs with 16 Threads, 64GiB RAM compute hosts) to offer all flavors.
Note: Compared to previous drafts, we have heavily reduced the variations
on disk sizes — this reflects that for the standard networked cinder
disks, you can pass blockdevice_mapping_v2 on server (VM) creation to
allocate a boot disk of any size you desire. We have scaled the few
mandatory disk sizes with the amount of RAM. For each flavor there is
also one _without a pre-attached disk — these are meant to be used
to boot from a volume (either created beforehand or allocated on-the-fly
with block_device_mapping_v2, e.g.
openstack server create --flavor SCS-1V:2 --block-device-mapping sda=IMGUUID:image:12:true
to create a bootable 12G cinder volume from image IMGUUID that gets tied to the VM
instance lifecycle.)
Naming policies
To be certified as an SCS compliant x86-64 IaaS platform, you must offer all standard SCS flavors according to the previous section. (We may define a mechanism that allows exceptions to be granted in a way that makes this very transparent and visible to clients.)
You are allowed to understate your performance; you may implement a SCS-1Vl:1:5 flavor with a flavor that actually implements SCS-1T:1:5n (i.e. you dedicate a secured hyperthread instead of high oversubscription) or even SCS-1D:1.5:8s (1 dedicated core, 50% more RAM and a 8GiB SSD).
We expect all cloud providers to offer the short, less specific flavor names (such as SCS-8V:32:100). Larger providers that offer more details are expected to still also offer the short variants for usability and easier portability, even beyond the mandated flavors.
You must be very careful to expose low vCPU guarantees (L instead ov V), insecure
hyperthreading/microcode i, non-ECC-RAM u, memory oversubscription o. Note that omitting these qualifiers is
overstating your security, reliability or performance properties and may be reason for
clients to feel betrayed or claim damages. It might in extreme cases also cause SCS to withdraw certification
along with public statements.
You may offer additional SCS- flavors, following the naming scheme outlined here.
You may offer additional flavors, not following above scheme.
You must not offer flavors with the SCS- prefix which do not follow this naming scheme. You must not extend the SCS naming scheme with your own suffices; you are encouraged however to suggest extensions that we can discuss and add to the official scheme.
Note that all letters are case-sensitive. In case you wonder: Feature indicators are capitalized, modifiers are lower case. (An exception is the uppercase -G for a passthrough GPU vs. lowercase -g for vGPU.)
Rationale
Note that we expect most clouds to prefer short flavor names, not indicating CPU details or hypervisor types. See above list of standard flavors to get a feeling.
However, more successful providers will often need to differentiate their
offerings in response to customer demand and allow customers to request
flavors with specific detailed properties. The goal of this proposal is to avoid
providers to invent their own names and then refer customers to extra_specs
or worse a non-machine-readable service description to find out the details.
So a cloud provider might well evolve from offering SCS-8T:16:50 to offering
SCS-8T:16:50n, SCS-8T:16:50n-i2 and SCS-8T:16:50n-a2 to specify that he
is using network disks and offer a choice b/w intel Cascade-Lake and AMD Rome.
We would expect the cloud provider to still offer the generic flavor
SCS-8C:16:50 and allow the scheduler (placement service) to pick both more
specific types (or just one if e.g. capacity management considerations suggest
so). We would expect providers in such cases to ensure that the price of a requested
flavor does not depend on the scheduler decisions.
We are looking into the metadefs mechanism and extra_specs to allow customers to ask for specific flavor properties without the need to encode all these flavor details into the flavor name, so the optional pieces may not be needed much. However, there must be a way to request flavor properties without encoding the need into an image — this indirection is considered broken by the SCS team.
Validation
There is a script in flavor_name_check.py which can be used to decode, validate and construct flavor names. This script must stay in sync with the specification text.
Ensure you have your OpenStack tooling (python3-openstackclient, OS_CLOUD) setup and call
tools/flavor-name-check.py -c $(openstack flavor list -f value -c Name) to get a report
on the flavor list compliance of the cloud environment.
Beyond SCS: Gaia-X
Some providers might offer VM services ("IaaS") without trying to adhere to SCS standards, yet still finding the flavor naming standards useful. The Gaia-X Technical Committee's Provider Working Group (WG) would seem like a logical place for such dicussions then. If so, we could replace the SCS- prefix with a GX- prefix and transfer the naming scheme governance from the SCS project to the Gaia-X Provider WG (where we participate). SCS certification would then reference the Gaia-X flavor naming standard as a requirement.