net: extend shared infrastructure for dual-stream cluster tests

Dual-stream clusters (RHCOS 9 + RHCOS 10 worker nodes) require VM
factory functions to support node pinning so tests can control which
node a VM starts on and verify migration between OS versions. Without
this, existing factories always use anti-affinity scheduling, making
deterministic migration direction impossible.

- Add mixed_os_nodes marker to pytest.ini to select tests only on
  compatible clusters
- Add rhcos9_node/rhcos10_node fixtures to network conftest
- Extend localnet_vm and udn_vm with optional node param for nodeSelector
- Add update_vm_node_selector helper and HOSTNAME_LABEL to nodes lib

Signed-off-by: Asia Khromov <azhivovk@redhat.com>
Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

Author: azhivovk

libs/net/ip.py

@@ -128,3 +128,23 @@ def have_same_ip_families(
     expected_ips: list[ipaddress.IPv4Address | ipaddress.IPv6Address],
 ) -> bool:
     return {ip.version for ip in actual_ips} == {ip.version for ip in expected_ips}
+
+
+def cidr_addresses_by_family(net_seed: int, host_address: int) -> list[str]:
+    """Return CIDR-formatted addresses for each IP family supported by the cluster.
+
+    IPv4 addresses use a /24 prefix; IPv6 addresses use /64. Only families
+    supported by the cluster are included. Suitable for any VM interface
+    configuration that needs per-family addresses (primary, secondary, UDN, etc.).
+
+    Args:
+        net_seed: Index into the cached pool of random network prefixes.
+        host_address: Host portion of the address — must be unique per VM in the test.
+
+    Returns:
+        List of CIDR strings (e.g. ["192.168.1.1/24", "fd00::1/64"]).
+    """
+    return [
+        f"{ip}/64" if ipaddress.ip_address(ip).version == 6 else f"{ip}/24"
+        for ip in random_ip_addresses_by_family(net_seed=net_seed, host_address=host_address)
+    ]

libs/vm/spec.py

@@ -31,6 +31,7 @@ class VMISpec:
     volumes: list[Volume] | None = None
     terminationGracePeriodSeconds: int | None = None  # noqa: N815
     affinity: Affinity | None = None
+    nodeSelector: dict[str, str] | None = None  # noqa: N815
 
 
 @dataclass

pytest.ini

@@ -72,6 +72,7 @@ markers =
     rwx_default_storage: Tests that require RWX storage
     descheduler: Tests that require kube-descheduler on nodes
     remote_cluster: Tests that require a remote cluster
+    mixed_os_nodes: Tests that require a dual-stream cluster with both RHCOS 9 and RHCOS 10 worker nodes
 
     ## Required operators
     mtv: Tests that require the MTV operator to be installed

tests/network/conftest.py

@@ -15,6 +15,11 @@
 from timeout_sampler import TimeoutExpiredError
 
 from libs.net.cluster import ipv4_supported_cluster, ipv6_supported_cluster
+from tests.network.libs.nodes import (
+    RHCOS_9_VERSION_PREFIX,
+    RHCOS_10_VERSION_PREFIX,
+    node_by_rhcos_version,
+)
 from tests.network.utils import get_vlan_index_number
 from utilities.constants import (
     CLUSTER,
@@ -321,3 +326,13 @@ def _verify_mtv_installed():
             message="Network cluster verification failed",
             admin_client=admin_client,
         )
+
+
+@pytest.fixture(scope="module")
+def rhcos9_node(workers):
+    return node_by_rhcos_version(workers=workers, rhcos_version_prefix=RHCOS_9_VERSION_PREFIX)
+
+
+@pytest.fixture(scope="module")
+def rhcos10_node(workers):
+    return node_by_rhcos_version(workers=workers, rhcos_version_prefix=RHCOS_10_VERSION_PREFIX)

tests/network/libs/nodes.py

@@ -0,0 +1,41 @@
+from typing import Final
+
+from ocp_resources.node import Node
+from ocp_resources.resource import ResourceEditor
+
+from libs.vm.vm import BaseVirtualMachine
+
+HOSTNAME_LABEL: Final[str] = "kubernetes.io/hostname"
+RHCOS_9_VERSION_PREFIX: Final[str] = "Red Hat Enterprise Linux CoreOS 9"
+RHCOS_10_VERSION_PREFIX: Final[str] = "Red Hat Enterprise Linux CoreOS 10"
+
+
+def node_by_rhcos_version(workers: list[Node], rhcos_version_prefix: str) -> Node:
+    """Return the first worker node whose OS image starts with the given RHCOS version prefix.
+
+    Args:
+        workers: List of worker nodes to search.
+        rhcos_version_prefix: Expected prefix of the node osImage field (e.g. "Red Hat Enterprise Linux CoreOS 9").
+
+    Returns:
+        The first matching Node.
+
+    Raises:
+        ValueError: If no worker node matches the prefix.
+    """
+    for node in workers:
+        if node.instance.status.nodeInfo.osImage.startswith(rhcos_version_prefix):
+            return node
+    raise ValueError(f"No worker node found with RHCOS version prefix: {rhcos_version_prefix!r}")
+
+
+def update_vm_node_selector(vm: BaseVirtualMachine, node: Node) -> None:
+    """Patch the VM spec to pin it to the given node via nodeSelector.
+
+    Args:
+        vm: VirtualMachine to update.
+        node: Target worker node.
+    """
+    ResourceEditor(
+        patches={vm: {"spec": {"template": {"spec": {"nodeSelector": {HOSTNAME_LABEL: node.hostname}}}}}}
+    ).update()

tests/network/libs/vm_factory.py

@@ -1,11 +1,13 @@
 """This module provides various virtual machine configurations with a focus on network setups."""
 
 from kubernetes.dynamic import DynamicClient
+from ocp_resources.node import Node
 
 from libs.net.udn import udn_primary_network
 from libs.vm.affinity import new_pod_anti_affinity
 from libs.vm.factory import base_vmspec, fedora_vm
 from libs.vm.vm import BaseVirtualMachine
+from tests.network.libs.nodes import HOSTNAME_LABEL
 
 
 def udn_vm(
@@ -15,12 +17,33 @@ def udn_vm(
     binding: str,
     template_labels: dict | None = None,
     anti_affinity_namespaces: list[str] | None = None,
+    node: Node | None = None,
 ) -> BaseVirtualMachine:
+    """Create a Fedora VM connected to a primary UDN using the specified binding.
+
+    When node is provided the VM is pinned to that node via nodeSelector and no
+    anti-affinity is applied. When template_labels are provided without a node,
+    pod anti-affinity is used for scheduling.
+
+    Args:
+        namespace_name: Namespace in which the VM will be created.
+        name: Name of the VM.
+        client: Kubernetes dynamic client.
+        binding: UDN binding plugin name (e.g. UDN_BINDING_DEFAULT_PLUGIN_NAME).
+        template_labels: Optional labels to add to the VM pod template, also used as anti-affinity key.
+        anti_affinity_namespaces: Optional namespaces to scope the pod anti-affinity rule.
+        node: If provided, pins the VM to this node via nodeSelector (takes precedence over anti-affinity).
+
+    Returns:
+        Configured BaseVirtualMachine object (not yet started).
+    """
     spec = base_vmspec()
     iface, network = udn_primary_network(name="udn-primary", binding=binding)
     spec.template.spec.domain.devices.interfaces = [iface]  # type: ignore
     spec.template.spec.networks = [network]
-    if template_labels:
+    if node is not None:
+        spec.template.spec.nodeSelector = {HOSTNAME_LABEL: node.hostname}
+    elif template_labels:
         spec.template.metadata.labels = spec.template.metadata.labels or {}  # type: ignore
         spec.template.metadata.labels.update(template_labels)  # type: ignore
         # Use the first label key and first value as the anti-affinity label to use:

tests/network/localnet/liblocalnet.py

@@ -6,6 +6,7 @@
 
 from kubernetes.client import ApiException
 from kubernetes.dynamic import DynamicClient
+from ocp_resources.node import Node
 
 from libs.net.cluster import ipv4_supported_cluster, ipv6_supported_cluster
 from libs.vm.affinity import new_pod_anti_affinity
@@ -16,6 +17,7 @@
 from tests.network.libs import cluster_user_defined_network as libcudn
 from tests.network.libs import nodenetworkconfigurationpolicy as libnncp
 from tests.network.libs.label_selector import LabelSelector
+from tests.network.libs.nodes import HOSTNAME_LABEL
 from utilities.constants import OVS_BRIDGE, WORKER_NODE_LABEL_KEY
 
 LOCALNET_BR_EX_NETWORK = "localnet-br-ex-network"
@@ -80,6 +82,7 @@ def localnet_vm(
     interfaces: list[Interface],
     network_data: cloudinit.NetworkData | None = None,
     affinity: Affinity | None = None,
+    node: Node | None = None,
 ) -> BaseVirtualMachine:
     """
     Create a Fedora-based Virtual Machine connected to localnet network(s).
@@ -98,8 +101,8 @@ def localnet_vm(
             Each Interface should have a name matching a Network, and additional configuration and state.
         network_data (cloudinit.NetworkData | None): Cloud-init NetworkData object containing the network
             configuration for the VM interfaces. If None, no network configuration is applied via cloud-init.
-        affinity (Affinity | None): Optional Affinity object for VM scheduling. Controls the VM scheduling
-            location. If None, no affinity constraints are applied.
+        affinity (Affinity | None): Optional Affinity object for VM scheduling. If None, no affinity is applied.
+        node (Node | None): If provided, pins the VM to this node via nodeSelector.
 
     Returns:
         BaseVirtualMachine: The configured VM object ready for creation.
@@ -141,6 +144,8 @@ def localnet_vm(
         )
         vmi_spec = add_volume_disk(vmi_spec=vmi_spec, volume=volume, disk=disk)
 
+    if node is not None:
+        vmi_spec.nodeSelector = {HOSTNAME_LABEL: node.hostname}
     if affinity is not None:
         vmi_spec.affinity = copy.deepcopy(affinity)