feat(openstack): add Linux bridge support to network_data.json

[s3rj1k]

Add support for converting OpenStack network_data.json "linux_bridge" link type to cloud-init network config v1 bridge type. This enables guest-side Linux bridge configuration through the OpenStack metadata service and config drive.

Related-To: https://review.opendev.org/c/openstack/nova/+/973924

[holmanb]

Thanks for this @s3rj1k. Please include a sample network_data.json from the metadata service and a cloud-init.log and cloud-init-output.log from an instance that was booted using this code.

[s3rj1k]

Hey @holmanb, sorry for delay, so I test this PR manually like so: https://gist.github.com/s3rj1k/6e90f63e4084beff4b064e23c79169ad

network_data.json (also in guide above):

{
  "links": [
    {
      "id": "interface0",
      "name": "eth0",
      "type": "phy",
      "ethernet_mac_address": "52:54:00:12:34:02",
      "mtu": 1500
    },
    {
      "id": "bridge0",
      "name": "br0",
      "type": "linux_bridge",
      "ethernet_mac_address": "52:54:00:12:34:02",
      "bridge_links": ["interface0"]
    }
  ],
  "networks": [
    {
      "id": "network0",
      "type": "ipv4_dhcp",
      "link": "bridge0",
      "network_id": "da5bb487-5193-4a65-a3df-4a0055a8c0d7"
    }
  ],
  "services": [
    {
      "type": "dns",
      "address": "8.8.8.8"
    },
    {
      "type": "dns",
      "address": "8.8.4.4"
    }
  ]
}

Requested logs are attached.
cloud-init-output.log
cloud-init.log

From logs I see:

2026-01-27 21:05:17,415 - DataSourceConfigDrive.py[DEBUG]: network config provided via network_json
2026-01-27 21:05:17,417 - atomic_helper.py[DEBUG]: Atomically writing to file /var/lib/cloud/instance/network-config.json (via temporary file /var/lib/cloud/instance/tmp4e0mifni) - w: [600] 457 bytes/chars
2026-01-27 21:05:17,418 - util.py[DEBUG]: Creating symbolic link from '/run/cloud-init/network-config.json' => '/var/lib/cloud/instance/network-config.json'
2026-01-27 21:05:17,418 - util.py[DEBUG]: Reading from /usr/lib/python3/dist-packages/cloudinit/config/schemas/schema-network-config-v1.json (quiet=False)
2026-01-27 21:05:17,418 - util.py[DEBUG]: Reading 22494 bytes from /usr/lib/python3/dist-packages/cloudinit/config/schemas/schema-network-config-v1.json
2026-01-27 21:05:17,423 - schema.py[WARNING]: network-config-v1 failed schema validation! You may run 'sudo cloud-init schema --system' to check the details.
2026-01-27 21:05:17,424 - networking.py[DEBUG]: net: all expected physical devices present
2026-01-27 21:05:17,442 - stages.py[INFO]: Applying network configuration from ds bringup=False: {'version': 1, 'config': [{'name': 'eth0', 'type': 'physical', 'mtu': 1500, 'subnets': [], 'mac_address': '52:54:00:12:34:02'}, {'name': 'br0', 'type': 'bridge', 'subnets': [{'type': 'dhcp4'}], 'mac_address': '52:54:00:12:34:02', 'bridge_interfaces': ['eth0']}, {'type': 'nameserver', 'address': '8.8.8.8'}, {'type': 'nameserver', 'address': '8.8.4.4'}]}
2026-01-27 21:05:17,443 - util.py[DEBUG]: Writing to /run/cloud-init/sem/apply_network_config.once - wb: [644] 24 bytes

and network config as expected:

root@vm-openstack:/home/ubuntu# ip -d a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 promiscuity 0  allmulti 0 minmtu 0 maxmtu 0 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535 tso_max_size 524280 tso_max_segs 65535 gro_max_size 65536
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host noprefixroute
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel master br0 state UP group default qlen 1000
    link/ether 52:54:00:12:34:02 brd ff:ff:ff:ff:ff:ff promiscuity 1  allmulti 1 minmtu 68 maxmtu 65535
    bridge_slave state forwarding priority 32 cost 100 hairpin off guard off root_block off fastleave off learning on flood on port_id 0x8001 port_no 0x1 designated_port 32769 designated_cost 0 designated_bridge 8000.52:54:0:12:34:2 designated_root 8000.52:54:0:12:34:2 hold_timer    0.00 message_age_timer    0.00 forward_delay_timer    0.00 topology_change_ack 0 config_pending 0 proxy_arp off proxy_arp_wifi off mcast_router 1 mcast_fast_leave off mcast_flood on bcast_flood on mcast_to_unicast off neigh_suppress off group_fwd_mask 0 group_fwd_mask_str 0x0 vlan_tunnel off isolated off locked off numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535 tso_max_size 65536 tso_max_segs 65535 gro_max_size 65536 parentbus virtio parentdev virtio0
3: br0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether 52:54:00:12:34:02 brd ff:ff:ff:ff:ff:ff promiscuity 0  allmulti 0 minmtu 68 maxmtu 65535
    bridge forward_delay 1500 hello_time 200 max_age 2000 ageing_time 30000 stp_state 0 priority 32768 vlan_filtering 0 vlan_protocol 802.1Q bridge_id 8000.52:54:0:12:34:2 designated_root 8000.52:54:0:12:34:2 root_port 0 root_path_cost 0 topology_change 0 topology_change_detected 0 hello_timer    0.00 tcn_timer    0.00 topology_change_timer    0.00 gc_timer   68.32 vlan_default_pvid 1 vlan_stats_enabled 0 vlan_stats_per_port 0 group_fwd_mask 0 group_address 01:80:c2:00:00:00 mcast_snooping 1 no_linklocal_learn 0 mcast_vlan_snooping 0 mcast_router 1 mcast_query_use_ifaddr 0 mcast_querier 0 mcast_hash_elasticity 16 mcast_hash_max 4096 mcast_last_member_count 2 mcast_startup_query_count 2 mcast_last_member_interval 100 mcast_membership_interval 26000 mcast_querier_interval 25500 mcast_query_interval 12500 mcast_query_response_interval 1000 mcast_startup_query_interval 3125 mcast_stats_enabled 0 mcast_igmp_version 2 mcast_mld_version 1 nf_call_iptables 0 nf_call_ip6tables 0 nf_call_arptables 0 numtxqueues 1 numrxqueues 1 gso_max_size 65536 gso_max_segs 65535 tso_max_size 65536 tso_max_segs 65535 gro_max_size 65536
    inet 192.168.122.245/24 metric 100 brd 192.168.122.255 scope global dynamic br0
       valid_lft 2852sec preferred_lft 2852sec
    inet6 fe80::5054:ff:fe12:3402/64 scope link
       valid_lft forever preferred_lft forever

[s3rj1k]

hmm, email does not match with CLA?

[s3rj1k]

@holmanb just wondering if we can remove "incomplete" label for this or am I still missing something?