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fix(vm-instance): supply cloud-init network-data to netplan guests - #4306
Aleksei Sviridkin (lexfrei) merged 2 commits into
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Included review availability: This review used your included allowance. Your plan provides up to 8 included reviews per hour; 7 remain after this review. 📝 WalkthroughWalkthroughThe VM chart adds an opt-in ChangesNetplan network-data
Priority: ➖ Normal Estimated code review effort: 3 (Moderate) | ~20 minutes Change: Bug fix Sequence Diagram(s)sequenceDiagram
participant HelmValues
participant NetworkConfigTemplate
participant VmTemplate
participant CloudInitDisk
HelmValues->>NetworkConfigTemplate: Enable network-data with netplanDhcp
VmTemplate->>CloudInitDisk: Include disk and set networkDataSecretRef
CloudInitDisk->>NetworkConfigTemplate: Use rendered network-config Secret
Suggested reviewers: Merge Risk: 🟡 Moderate · up to Users enabling DHCP for a VM with the documented static external-VLAN setup can lose its static network address. Resolve or explicitly accept this interaction before merging. Architecture SummaryArchitecture risk: 🔵 Low · up to The change affects 4 systems. Changed systems: Architecture concerns Review detailsSystems and components
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In `@packages/apps/vm-instance/templates/secret-network-config.yaml`:
- Around line 32-43: Redesign the generated Netplan definitions around cozy-en
and cozy-eth so broad interface matching cannot compete with a user-defined
static VLAN or enp2s0 configuration; preserve DHCP behavior for the intended
interfaces while ensuring static addresses are applied. Update the external VLAN
documentation to remove the claim that the 60-vlan100.yaml recipe overrides this
configuration.
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docs/vm-external-vlan.mdpackages/apps/vm-instance/templates/_helpers.tplpackages/apps/vm-instance/templates/secret-network-config.yamlpackages/apps/vm-instance/templates/vm.yamlpackages/apps/vm-instance/tests/network_data_test.yaml
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Aleksei Sviridkin (lexfrei)
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mattia-eleuteri NOT LGTM. The network-data is right for a netplan guest that is actually tagged ubuntu or debian, but the gate also catches guests that are not netplan, and the network-data breaks the external-VLAN recipe that the updated doc calls compatible.
B1. The gate matches the chart default, so it is not narrow. instanceProfile defaults to ubuntu in values.yaml, so every VM created without touching that field gets the v2 network-data, whatever image its disk holds. Non-netplan renderers turn the match stanza into an interface named after the definition ID. I ran the rendered network-data through cloud-init devel net-convert (cloud-init 26.1):
sysconfig: ifcfg-cozy-en DEVICE=cozy-en
network-manager: cloud-init cozy-en.nmconnection interface-name=cozy-en
eni: auto cozy-en / iface cozy-en inet dhcp
None of them configures the real NIC, and network-data from the datasource replaces the fallback config. So an AlmaLinux, Rocky or Alpine image left on the default profile loses the DHCP it gets today. This is the exact failure the helper comment describes, reachable through the default value. Your first alternative, an explicit values key that is off by default, avoids it. I'd take that one.
B2. The external-VLAN recipe stops working, and the new gotcha says it doesn't conflict. Netplan writes one networkd file per definition ID, and systemd-networkd applies only the first .network file in lexical order that matches a link (systemd.network(5)). With the chart's 50-cloud-init.yaml and the recipe's 60-vlan100.yaml in /etc/netplan, netplan generate on Ubuntu 24.04 gives:
10-netplan-cozy-en.network [Match] Name=en* DHCP=ipv4
10-netplan-cozy-eth.network [Match] Name=eth* DHCP=ipv4
10-netplan-enp2s0.network [Match] Name=enp2s0 Address=203.0.113.10/24
cozy-en sorts before enp2s0, so enp2s0 gets the DHCP file and the static address is never applied. "A higher-numbered file wins" holds only for keys under the same ID. This is the conflict CodeRabbit flagged on secret-network-config.yaml, still unanswered. With an opt-in key the doc can say not to enable it on a VM that has a static NIC; without one the chart has to stop matching interfaces the user configures.
B3. Existing VMs without cloudInit and sshKeys change on their next restart. For such a VM on the default profile, the upgrade adds a cloudinitdisk volume where there was none. KubeVirt uses the pinned firmware UUID as the NoCloud instance-id (cloudInitUUIDFromVMI in pkg/cloud-init), and the guest has never seen that id, so cloud-init runs as on a first boot: new SSH host keys, a new netplan file. The PR body, which becomes the merge commit message, says existing VMs are unaffected until they are recreated. That holds only for VMs that already had a cloud-init disk. An opt-in key fixes this as well.
Non-blocking: the helper comment in _helpers.tpl explains how the gate relates to the old virtual-machine chart and systemDisk.image. The commit message already carries that history, and the comment reads fine with just the netplan-renderer reason.
The trial merge with current main is clean and helm unittest passes there (66 tests). The new suite catches the two mutations I tried: forcing the gate on, and dropping the disk condition.
| */}} | ||
| {{- define "virtual-machine.netplanGuest" -}} | ||
| {{- $profile := toString .Values.instanceProfile -}} | ||
| {{- if or (hasPrefix "ubuntu" $profile) (hasPrefix "debian" $profile) -}} |
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instanceProfile defaults to ubuntu, so this is true for every VM that never set the field, including non-netplan images. See B1 in the review body for the sysconfig, NetworkManager and eni renders.
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Replaced in 403e5fd by an explicit netplanDhcp value, off by default; the helper is gone and instanceProfile no longer plays any part. The template comment now says why the gate is not the profile, and tests/network_data_test.yaml asserts that a VM on the default profile renders neither the Secret nor a cloud-init disk.
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| - **VMs are dual-homed.** The `vm-instance` chart always adds the pod-network NIC in addition to any `networks` you declare; there is no single-homed (VLAN-only) option today. Address the VLAN NIC inside the guest and leave the pod NIC to the cluster. | ||
| - **No `networkData`.** The chart wires cloud-init through `userData` only, so in-guest static configuration (netplan `write_files` + `netplan apply`, as above) is the way to assign the VLAN address. | ||
| - **`networkData` is the chart's, not yours.** For a guest whose `instanceProfile` is `ubuntu` or `debian` the chart supplies its own cloud-init network-data, asking every `en*` and `eth*` interface for DHCP, and there is no value that replaces it. It does not conflict with the recipe above — netplan merges `/etc/netplan/*.yaml`, and a higher-numbered file wins — but a static address still has to come from `userData`, as above. |
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This doesn't hold. The IDs differ (cozy-en vs enp2s0), so netplan emits two .network files and networkd applies 10-netplan-cozy-en.network first; the static address is dropped. Render in B2.
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Right, reproduced with netplan generate on Ubuntu 24.04: 10-netplan-cozy-en.network sorts before 10-netplan-enp2s0.network and the static address is dropped. The gotcha now says the opposite: leave netplanDhcp off on a VM with a static NIC, with the one-file-per-ID and first-match reasons, and step 3 says the recipe keeps it off.
| name: vm-disk-{{ .name }} | ||
| {{- end }} | ||
| {{- if or .Values.cloudInit .Values.sshKeys }} | ||
| {{- if or .Values.cloudInit .Values.sshKeys $netplanGuest }} |
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On upgrade this adds a cloud-init disk to an existing default-profile VM that had none, and cloud-init treats the next boot as a new instance (B3).
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With the gate on netplanDhcp, a VM that leaves it unset gets no cloud-init disk it did not already have. The value description states that turning it on for a VM with neither cloudInit nor sshKeys makes the next boot a first boot, and the PR body no longer claims existing VMs are unaffected across the board.
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Aleksei Sviridkin (@lexfrei) all three hold, and 403e5fd takes the explicit value you suggested. B1. The network-data is now behind B2. Reproduced with B3. A VM that leaves the value unset renders exactly as before, no Secret and no cloud-init disk, and a test pins that on the default profile. The value description warns that turning it on for a VM with neither Non-blocking: the helper is removed, and the only comment left on the template gives the renderer reason for not keying on the profile. With the templates gated on the |
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mattia-eleuteri NOT LGTM, only because the branch no longer merges. The three blockers from my last review are fixed, and I have nothing left on the code.
The branch conflicts with main in packages/apps/vm-instance/README.md and packages/system/vm-instance-rd/cozyrds/vm-instance.yaml. Both files are generated, so please rebase and run make generate instead of merging them by hand. Main's pre-commit moved to cozyvalues-gen v1.7.0 after your merge base, which still had v1.6.0, so the regenerated output may differ from what is committed now. Because of the conflict, pre-commit and E2E Tests never ran on 403e5fd. I'll approve once the rebased head is green.
What I checked on 403e5fd:
- With
netplanDhcpunset, the chart renders byte for byte like main on six value sets: defaults,cloudInit,sshKeys, one network, two networks with user-data, andcloudInitSeed. With it on, the only additions are the Secret, thecloudinitdiskdisk and volume, andnetworkDataSecretRef. KubeVirt v1.9.0 accepts acloudInitNoCloudvolume that has network-data and no user-data. - The Step 3 text and the new gotcha in
docs/vm-external-vlan.mdnow match what netplan and networkd do. - Your instance-id sentence and my B3 don't contradict each other, and both hold. KubeVirt v1.9.0 takes the NoCloud instance-id from the firmware UUID (
cloudInitUUIDFromVMI, pkg/cloud-init/cloud-init.go:113-117, used at :141 and :587). The chart pins that UUID to a hash of namespace, fullname andcloudInitSeed(virtual-machine.stableUuid, _helpers.tpl:56-70, rendered at vm.yaml:71). So recreating the VM keeps the id, and changing the seed changes it. values.schema.json, the README andtypes.gomatch what cozyvalues-gen v1.6.0 produces fromvalues.yamlat this head.- helm unittest passes, 32 tests at the head and 65 on a trial merge with current main. Five mutations all go red: the default flipped to true, the Secret gate removed,
netplanDhcpdropped from the disk condition, thenetworkDataSecretRefgate removed, and the user-datasecretRefmade unconditional. - Both commits are signed off with your address, and the new commit message is fine.
Not blocking: 6cb38bc still carries the profile-keyed gate and the old gotcha at its own SHA. The repo merges with merge commits, so both commits land on main, and a bisect over vm-instance can stop on the version that drops DHCP for non-netplan guests. Since you are rebasing anyway, squashing the two commits avoids that.
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mattia-eleuteri I rebased the branch onto current main. It conflicted only in the generated vm-instance README and ApplicationDefinition, so I took main's copies and regenerated them with cozyvalues-gen 1.7.0, which CI pins now. The change is the same one I reviewed in 5354607551.
A netplan guest configures only the interface cloud-init's fallback configuration covers, and keeps none of the search domains DHCP offers it, so two things the platform already puts on the wire never reach it. virt-launcher runs a DHCP server on every bridge-bound interface, secondary ones included, yet a VM joined to a VPC subnet leaves that interface inert for want of a client asking. The same server advertises the launcher pod's search domains as option 119, which systemd-networkd discards because UseDomains= defaults to no, and a cluster domain under .local then falls through to the mDNS exclusion in resolved and answers REFUSED. The virtual-machine chart carried a network-data template for the first of those, gated on systemDisk.image. Splitting that chart into vm-disk and vm-instance removed the template along with the field it read, and neither came back. Matching en* and eth* rather than naming interfaces by index keeps the configuration correct whatever the guest enumerates its NICs as, which is where the previous template was fragile. Assisted-by: LLM Signed-off-by: Mattia Eleuteri <[email protected]>
Keying the network-data on instanceProfile reached every VM that never set the field, because the profile defaults to ubuntu whatever image the disk holds. The sysconfig, NetworkManager and eni renderers turn each match stanza into an interface literally named after the netplan ID, so a non-netplan guest left on the default profile would lose the DHCP it gets today. A VM with neither cloudInit nor sshKeys would also gain a cloud-init disk on upgrade, and KubeVirt's NoCloud instance-id is new to that guest, so its next boot would regenerate host keys as a first boot. The configuration also shadows a static NIC set up through netplan: netplan emits one networkd file per ID, networkd applies only the first file in lexical order that matches a link, and 10-netplan-cozy-en sorts before the file for enp2s0. The external-VLAN recipe claimed otherwise. An explicit netplanDhcp value, off by default, leaves every existing VM rendering exactly as before and lets the documentation say when not to turn it on. Assisted-by: LLM Signed-off-by: Mattia Eleuteri <[email protected]>
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mattia-eleuteri I rebased this onto current main and resolved the conflicts. They were only in the generated README table and the cozyrds file, so I regenerated both with cozyvalues-gen v1.7.0, the version CI uses. The chart change itself is the same as the one I approved.
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What this PR does
A guest whose interfaces are rendered by netplan ignores two things the platform already puts on the wire for it, and this adds an opt-in
netplanDhcpvalue that supplies the cloud-init network-data making it ask for both.virt-launcherstarts a DHCP server on every bridge-bound interface, secondary ones included —newDHCPConfiguratorinpkg/network/setup/launcher/configurator.gogates only oniface.Bridge != nil, andBridgeConfigGenerator.Generateserves the address the CNI put on the pod-side interface along with that link's MTU. The chart rendersbridge: {}for every network, so a VM joined to a VPC subnet is offered its reserved address and its MTU. cloud-init's fallback network configuration covers a single interface, so on Debian and Ubuntu nothing ever sends a DHCPDISCOVER on the second NIC and the interface stays inert, while AlmaLinux (NetworkManager auto-profile) and Windows come up. That asymmetry is the tell: with no DHCP server at all, none of the three would work.The same DHCP server advertises the launcher pod's search domains as option 119, and
UseDomains=defaults tonoin systemd-networkd, so a netplan-managed link keeps none of them. A cluster domain under.localthen reaches the mDNS exclusion in resolved and every lookup answersREFUSED, which is #2085.dhcp4-overrides: use-domains: trueis enough on its own: the domains on the wire already carry whatever cluster domain the cluster actually uses, so nothing needs to be hardcoded here and #2372 does not collide with this.This is a regression, not a missing feature
packages/apps/virtual-machinecarried exactly this, added in c63fb20 ([apps] virtual-machine: add vpc support, 2025-10-21) astemplates/secret-network-config.yamlplus anetworkDataSecretRef, gated on.Values.systemDisk.image. 08a5f98 (feat(platform): remove virtual-machine application, 2026-02-12) deleted the application and the template with it, andvm-instancenever had one —git log --all -S networkDataSecretRef -- packages/apps/vm-instance/is empty. The gate could not be ported verbatim becausesystemDisk.imagewent away in the same split, which is the likeliest reason nobody did. #2166 is the other regression from that migration.docs/vm-external-vlan.mdhas since documented the absence as a property of the chart and prescribed awrite_files+netplan applyworkaround, so this PR updates that page too.Why it is opt-in
The network-data renders only when
netplanDhcpistrue, and the value defaults tofalse. Keying it oninstanceProfileinstead cannot work: the profile defaults toubuntuwhatever image the disk holds, and it is a KubeVirt preference rather than a declaration of the guest's network stack. cloud-init passes a v2 configuration through verbatim only for the netplan renderer; sysconfig, NetworkManager and eni turn eachmatchstanza into an interface literally namedcozy-enorcozy-eth, so a non-netplan guest handed this configuration loses DHCP on its real NIC.Two cases where the value must stay off, both stated in its description and in
docs/vm-external-vlan.md:.networkfile in lexical order that matches a link, so10-netplan-cozy-en.networkshadows10-netplan-enp2s0.networkand the static address is never applied, whatever number the user's netplan file carries. Reproduced withnetplan generateon Ubuntu 24.04.Matching by MAC with a v1 configuration would be renderer-independent and would not shadow a named interface, but it needs the chart to know the MACs at render time;
lookupcannot supply them on a first install, so the chart would have to pin them, which is a larger change that overlaps #4038.What this does not do
A VM that leaves
netplanDhcpunset renders exactly as before: no network-data Secret, and no cloud-init disk where there was none. Turning the value on for a VM with neithercloudInitnorsshKeysadds a cloud-init disk, and because KubeVirt uses the pinned firmware UUID as the NoCloud instance-id, a guest that has never seen that id treats its next boot as a first boot (new SSH host keys); the value's description says so. On a VM that already has a cloud-init disk the instance-id does not change, and it is derived from the namespace, the name andcloudInitSeed, so recreating the VM keeps it too; cloud-init applies network configuration per instance by default, so such a guest picks the network-data up oncecloudInitSeedis changed. Static addressing is stilluserData.Tests
tests/network_data_test.yaml, 6 cases: the rendered network-data asserted in full (both properties, not just the presence of the key), the VM carrying network-data with no user-data requested, user-data and network-data side by side, a VM on the default profile rendering neither the Secret nor a cloud-init disk, user-data alone when the value is off, and the value rather than the profile deciding. With the templates gated on theubuntuprofile again, the default-profile case and the value-off case go red.helm unittestgreen on all four suites of the package (32 tests).make generateoutput is committed (values.schema.json,README.md,api/apps/v1alpha1/vminstance/types.go,packages/system/vm-instance-rd/).helm lintfails on this package identically on an untouched tree (_cluster.schedulingnil pointer,cozy-libdependency metadata), so it is not a signal here.Screenshots
Not a UI change.
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