Ephemeral os disk

[HappyTobi]

Hi all,

the pr related to the issue #671
Still open:
robocop fixed (1)

Checklist:

Please check each of the boxes below for which you have completed the corresponding task:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works
• All unit tests pass locally (after my changes)
• Rubocop reports zero offenses (after my changes)

Please include below the summary portions of the output from the following 2 scripts:

pushd src/bosh_azure_cpi
  ./bin/test-unit
  ./bin/rubocop_check
popd

NOTE: Please see how to setup dev environment and run unit tests in docs/development.md.

Unit Test output:

1031 examples, 0 failures

Rubocop output:

Offenses:

lib/cloud/azure/vms/vm_manager.rb:22:5: C: Metrics/AbcSize: Assignment Branch Condition size for create is too high. [<85, 167, 47> 193.2/192]
    def create(bosh_vm_meta, location, vm_props, disk_cids, network_configurator, env, agent_settings, network_spec, config) ...
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

190 files inspected, 2 offenses detected, 1 offense auto-correctable

Changelog

Add Azure Ephemeral OS disk:
https://learn.microsoft.com/en-us/azure/virtual-machines/ephemeral-os-disks

Update bosh-cloud config to use ephemeral os disk:

"ephemeral_disk": {
      "size": 20480,
      "use_root_disk": true
    },
    "root_disk": {
      "placement": "cache-disk"
    }

New attribute at root_disk, placement
The placement can be set to: remote (default), cache-disk resource-disk

The disk calculation are change when use_root_disk is set to true and placement is different than remote.
The behaviour is that the size of the root and ephemeral disk are added together.

"ephemeral_disk": {
      "size": 20480,
      "use_root_disk": true
    },
    "root_disk": {
      "size": 30720,
      "placement": "cache-disk"
    }

will result in a ephemeral os disk with the size of 51200 placed on the vm cache disk.

Regards

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: HappyTobi / name: Tobias Schug (60fcfe0)

[HappyTobi]

@rkoster @beyhan feel free to review my pr.

Thx

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: HappyTobi / name: Tobias Schug (f724d3e)

[beyhan]

I have only the comment about the TODO otherwise it looks good to me.

[aramprice]

Would it be possible to squash down the commits in this PR? The merge from master, and various fix commits will not make git history easier to comprehend. -Thanks!

[HappyTobi]

I can squash them if you want, or some one else do it later when the pr will be merged.

[rkoster]

@HappyTobi could you squash the commits as @aramprice has asked? Also, Aram did you just look at the commit messages or did you perform a full review? If so could you add your review to github so we can merge?

[aramprice]

@rkoster the shape of this looks good to me but I don't have enough context on Azure to do a deep dive on the actual implementation.

[HappyTobi]

@rkoster rebase is done

[klakin-pivotal]

I'm the wrong one to give the PR a detailed evaluation, but I do have one question:

What happens if the largest temporary root disk that Azure is willing to provide is smaller than what we ask Azure for?

For context about my concern, notice that Size limit for OS disk row of the first table here https://learn.microsoft.com/en-us/azure/virtual-machines/ephemeral-os-disks, says:

Cache size or temp size for the VM size or 2040 GiB, whichever is smaller. For the cache or temp size in GiB, see DS, ES, M, FS, and GS

To see the maximum temporary storage limit for each machine type, go looking at the various machine sizes here https://learn.microsoft.com/en-us/azure/virtual-machines/sizes-general. (In particular, note that extremely budget-conscious customers might choose a Standard_B2s, which has a temporary storage limit of 8GB, or maybe a Standard_DS2_v2 which has a 14GB limit.)

Also, notice that some machine types don't have a local temporary disk. What happens if the VM size selected has no local temporary disk? https://learn.microsoft.com/en-us/azure/virtual-machines/azure-vms-no-temp-disk

[HappyTobi]

@klakin-pivotal
Thx for asking.

I'm the wrong one to give the PR a detailed evaluation, but I do have one question:

What happens if the largest temporary root disk that Azure is willing to provide is smaller than what we ask Azure for?

You will receive an error that the disk cache / resource disk is to big for the select vm-type. (Azure api error response)

For context about my concern, notice that Size limit for OS disk row of the first table here https://learn.microsoft.com/en-us/azure/virtual-machines/ephemeral-os-disks, says:

Cache size or temp size for the VM size or 2040 GiB, whichever is smaller. For the cache or temp size in GiB, see DS, ES, M, FS, and GS

To see the maximum temporary storage limit for each machine type, go looking at the various machine sizes here https://learn.microsoft.com/en-us/azure/virtual-machines/sizes-general. (In particular, note that extremely budget-conscious customers might choose a Standard_B2s, which has a temporary storage limit of 8GB, or maybe a Standard_DS2_v2 which has a 14GB limit.)

Also, notice that some machine types don't have a local temporary disk. What happens if the VM size selected has no local temporary disk? https://learn.microsoft.com/en-us/azure/virtual-machines/azure-vms-no-temp-disk

You also receive an error while creating the VM.

I think you have to think about disks and vm-types upfront before you start to deploy.
The default is like before so no one will run into an issue without changing anything explicit.

Lest take a look at the DSv2-series:
https://learn.microsoft.com/en-us/azure/virtual-machines/dv2-dsv2-series#dsv2-series
Standard_DS4_v2.
Here you can choose between: resource-disk with a max size of 56GB or a cache-disk with 344GB max size.
So it's like i mentioned before, it's important to check the sizes upfront.

With the implementations it's also possible to place the os_disk only to the resource or cache-disk and the ephemeral-disk to a "default" remote one, so the user have the complete choice / freedom to configure the disk for there use-case.

[klakin-pivotal]

Cool. If Azure sends back a response that causes the Bosh VM Creation task to fail, then that handles that concern.

Do you have examples of the error responses that we get back from Azure?

I'm concerned that they may not written well enough for an operator to understand what has gone wrong and how to correct it. If this is the case, we would be required to detect these error conditions and emit a better error message.

[HappyTobi]

@klakin-pivotal
sorry for the late reply.
The error message looks like:

Error message: {
  "error": {
    "code": "NotSupported",
    "message": "OS disk of Ephemeral VM with size greater than 50 GB is not allowed for VM size Standard_D2s_v3 when the DiffDiskPlacement is CacheDisk. Please refer to https://aka.ms/Ephemeral for more details."
  }
}

Think the message is fine to everyone understand what's wrong and where they get more information if required.

[rkoster]

Thanks @HappyTobi