Description

The new Beta FlatCar with version 3913.1.0 updated systemd to version 255. With this new version comes support for DHCP RapidCommit which seems to be enabled by default:

RapidCommit=

    Takes a boolean. The DHCPv4 client can obtain configuration parameters from a DHCPv4 server through a rapid two-message exchange (discover and ack). When the rapid commit option is set by both the DHCPv4 client and the DHCPv4 server, the two-message exchange is used. Otherwise, the four-message exchange (discover, offer, request, and ack) is used. The two-message exchange provides faster client configuration. See [RFC 4039](https://tools.ietf.org/html/rfc4039) for details. Defaults to true when Anonymize=no and neither AllowList= nor DenyList= is specified, and false otherwise.

    Added in version 255.

Our cloud provider (CloudSigma) seems to have a faulty implementation of DHCPv4 rapid commit which means that we are no longer getting an IP address.

This can be fixed (for existing servers) by copying the default config from /usr/lib/systemd/network/zz-default.network as an own config and adapting the DHCPv4 section as follows:

[DHCPv4]
RoutesToDNS=false
RapidCommit=false

Impact

Not getting an IP address. Because the CloudInit process for CloudSigma requires an assigned lease this also means that the whole setup doesn't work anymore.

Environment and steps to reproduce

1. Upload current beta FlatCar CloudSigma vendor image to CloudSigma
2. Create a new machine
3. No public IP is assigned and the CloudInit process never runs

Expected behavior

Server correctly setup with IP and CloudInit config.

Additional information

We are also in discussions with CloudSigma in order to fix their DHCP implementation. Not sure when and how this will go though.

This is not really a bug on Flatcars side but rather a break for us because the network config is now different with the new version.

The question is how this could be fixed (if you are open to do it on the FlatCar side). I currently see the following options:

• Update the default network config to disabled rapid commit
• Add a custom network config file to the vendored CloudSigma image

I would like to get some feedback for this and probably can provide a PR if you would be fine with one of the proposed solutions :).