Breaking changes

This section provides guidance on specific breaking changes to cloud-init releases.

Note

These changes may not be present in all distributions of cloud-init as many operating system vendors patch out breaking changes in cloud-init to ensure consistent behavior on their platform.

25.1.4

Strict datasource identity before network

Affects detection of Ec2, OpenStack or AltCloud datasources for non-x86 architectures where DMI may not be accessible.

Datasource detection provided by ds-identify in cloud-init now requires strict identification based on DMI platform information, kernel command line or datasource_list: system configuration in /etc/cloud/cloud.cfg.d.

Prior to this change, ds-identify would allow non-x86 architectures without strict identifying platform information to run in a discovery mode which would attempt to reach out to well known static link-local IPs to attempt to retrieve configuration once system networking is up.

To mitigate the potential of a bad-actor in a local network responding to such provisioning requests from cloud-init clients, ds-identify will no longer allow this late discovery mode for platforms unable to expose clear identifying characteristics of a known cloud-init datasource.

The most likely affected cloud platforms are AltCloud, Ec2 and OpenStack for non-x86 architectures where DMI data is not exposed by the kernel.

If your non-x86 architecture or images no longer detect the proper datasource, cloud-init will remain disabled and perform no configuration operations during boot.

Any of the following alternatives can ensure proper enablement of cloud-init in non-x86 images without DMI-data:

  • When launching VMs with the openstack command line client, provide --config-drive true:

$ openstack server create ... --config-drive true

  • On the openstack image command line, modify specific image metadata to require config drive for the image:

$ openstack image set <IMG_UUID> --property img_config_drive=mandatory

  • OpenStack image creators can place a config file in the image at /etc/cloud/cloud.cfg.d/91_openstack.cfg to force cloud-init to use OpenStack without DMI-based discovery. The file must contain a single datasource as follows:

datasource_list: [ OpenStack ]

  • Charmed OpenStack Admins using glance-simplestreams-sync can default all syncronized images to use config_drive:

$ juju config glance-simplestreams-sync custom-properties="img_config_drive=mandatory"

  • OpenStack Nova admins can globally configure Nova to provide config drives to all images by default in /etc/nova/nova.conf:

[DEFAULT]
force_config_drive = true

  • Alternatively, providing kernel command line arguments to a virtual machine containing ds=openstack will force ds-identify to use the specific datasource.

25.1

/usr merge

Cloud-init’s packaging code no longer installs anything to /lib. Instead, anything that was installed to /lib is now installed to /usr/lib. This shouldn’t affect any systemd-based distributions as they have all transitioned to the /usr merge. However, this could affect older stable releases, non-systemd and non-Linux distributions. See commit 054734921 for more details.

24.4

Cloud-init’s cloud-final.service order was standardized. This caused a change to the systemd boot order on some distributions. See commit 245f94674 for more details.

24.3

Single Process Optimization

As a performance optimization, cloud-init no longer runs as four seperate Python processes. Instead, it launches a single process and then communicates with the init system over a Unix socket to allow the init system to tell it when it should start each stage and to tell the init system when each stage has completed. Init system ordering is preserved.

This should have no noticable affect for end users, besides a faster boot time. This is labeled a breaking change for three reasons:

  1. this change included renaming a systemd service: cloud-init.service -> cloud-init-network.service

  2. new dependency on openbsd’s netcat implementation

  3. a precaution to avoid unintentionally breaking users on stable distributions

Any external services which are ordered after or depend on the old cloud-init.service name can safely switch to cloud-config.target, which should provide the same point in boot order before and after this change.

OpenBSD netcat is already included in many major distributions, however any distribution that wishes to avoid this dependency might prefer to use a Python3 equivalent one-liner. Upstream prefers OpenBSD netcat for performance reasons.

Any systemd distribution that wants to revert this behavior wholesale for backwards compatibility may want to use this patch.

Note

Support has not yet been added for non-systemd distributions, however it is possible to add support.

The command line arguments used to invoke each stage retain support for now to allow for adoption and stabilization.

Addition of NoCloud network-config

The NoCloud datasource now has support for providing network configuration using network-config. Any installation that doesn’t provide this configuration file will experience a retry/timeout in boot. Adding an empty network-config file should provide backwards compatibility with previous behavior.

24.1

Removal of --file top-level option

The --file top-level option has been removed from cloud-init. It only applied to a handful of subcommands so it did not make sense as a top-level option. Instead, --file may be passed to a subcommand that supports it. For example, the following command will no longer work:

cloud-init --file=userdata.yaml modules --mode config

Instead, use:

cloud-init modules --file=userdata.yaml --mode config

Removed Ubuntu’s ordering dependency on snapd.seeded

In Ubuntu releases, cloud-init will no longer wait on snapd pre-seeding to run. If a user-provided script relies on a snap, it must now be prefixed with snap wait system seed.loaded to ensure the snaps are ready for use. For example, a cloud config that previously included:

runcmd:
  - [ snap, install, mc-installer ]

Will now need to be:

runcmd:
  - [ snap, wait, system, seed.loaded ]
  - [ snap, install, mc-installer ]

23.2-24.1 - Datasource identification

23.2

If the detected datasource_list contains a single datasource or that datasource plus None, automatically use that datasource without checking to see if it is available. This allows for using datasources that don’t have a way to be deterministically detected.

23.4

If the detected datasource_list contains a single datasource plus None, no longer automatically use that datasource because None is a valid datasource that may be used if the primary datasource is not available.

24.1

ds-identify no longer automatically appends None to a datasource list with a single entry provided under /etc/cloud. If None is desired as a fallback, it must be explicitly added to the customized datasource list.

23.4 - added status code for recoverable error

Cloud-init return codes have been extended with a new error code (2), which will be returned when cloud-init experiences an error that it can recover from. See this page which documents the change.

23.2 - kernel command line

The ds= kernel command line value is used to forcibly select a specific datasource in cloud-init. Prior to 23.2, this only optionally selected the NoCloud datasource.

Anyone that previously had a matching ds=nocloud* in their kernel command line that did not want to use the NoCloud datasource may experience broken behavior as a result of this change.

Workarounds include updating the kernel command line and optionally configuring a datasource_list in /etc/cloud/cloud.cfg.d/*.cfg.