fix: conditionally set explicit hostname in Nova server create to prevent .novalocal suffix

[benedikt-haug]

Motivation

When Nova derives the OS hostname from the server display name, it appends the [api] dhcp_domain (commonly .novalocal). For Gardener shoot workers, the full machine name can exceed the 63-byte RFC 1123 label limit that Kubernetes enforces for the kubernetes.io/hostname node label, causing pod scheduling failures:

unable to parse requirement: values[0][kubernetes.io/hostname]:
Invalid value: "shoot--staging--kbo8cp525p-worker-ndrej-z3-58f8b-2t9lq.novalocal":
must be no more than 63 bytes

Additionally, the .novalocal suffix causes hostname instability across reboots (see gardener/gardener-extension-provider-openstack#569): cloud-init re-applies the FQDN on reboot, racing with the ExecStartPre workaround that strips the domain, leading to inconsistent hostnames and kubelet startup failures.

Background

Since Nova Wallaby (API microversion 2.90), the hostname field in POST /servers allows decoupling the OS hostname from the display name. When set, Nova uses this value directly in the metadata service — without appending dhcp_domain. The display name (Name) remains unaffected.

This was confirmed via a manual PoC against an OpenStack deployment (Nova max microversion 2.100):

• hostname field accepted with MV 2.90
• OS-EXT-SRV-ATTR:hostname stored the explicit value without .novalocal
• Normal VMs (without hostname field) remained unaffected

References:

• Nova spec: Configurable Instance Hostnames (Wallaby)
• API microversion 2.90 changelog
• gophercloud CreateOpts.Hostname field (available since v2.x, confirmed in v2.12.0)

Changes

1. pkg/client/nova.go: Conditionally pin the Nova compute client to microversion 2.90 using utils.GetSupportedMicroversions(), enabling the hostname field in server create requests. Falls back gracefully on older Nova deployments.

2. pkg/driver/executor/executor.go: Pass machineName as the explicit hostname in servers.CreateOpts only when SupportsHostnameOverride() returns true, decoupling the OS hostname from the display name.

3. pkg/client/types.go: Added SupportsHostnameOverride() bool to the Compute interface.

Supersedes #414 (closed due to accidental force-push). Incorporates all review feedback from @aaronfern and @AndreasBurger.

Fixes gardener/gardener-extension-provider-openstack#569

🤖 Generated with AI assistance — the code changes, analysis, and PoC verification were performed by an AI agent. The approach was validated manually against a live OpenStack deployment.

[federated-github-access]

The PR needs to be labeled with ok-to-test by a maintainer to trigger the automated validation of the change

[AndreasBurger]

/lgtm, thanks. Can you sign the commit as required by the DCO-check?

[federated-github-access]

The PR needs to be labeled with ok-to-test by a maintainer to trigger the automated validation of the change

[benedikt-haug]

/lgtm, thanks. Can you sign the commit as required by the DCO-check?

done

[aaronfern]

Thanks for the PR @benedikt-haug!
/lgtm
/approve

[gardener-prow]

LGTM label has been added.

Details

Git tree hash: cb2cb294397a42c9beb01495a51399e236cea40e

[aaronfern]

/kind enhancement

[gardener-prow]

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This pull-request has been approved by: aaronfern, AndreasBurger

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