Cloud-init templates are only as good as their first boot behavior, and the differences between Ubuntu, Debian, and Rocky Linux are real enough to affect reliability. At Raff Technologies, this matters because a template that looks clean in the image pipeline can still behave differently once it has to process metadata, inject SSH keys, bring networking up, and hand control back to the user on a fresh VM.
That is what makes cloud-init testing more interesting than it first sounds. You are not only testing whether an operating system supports cloud-init. You are testing whether the distribution’s defaults, packaging choices, boot order, and image state produce a first boot that feels predictable instead of fragile. Raff already has a live guide on VM provisioning models: cloud-init, custom images, and one-click apps, but this post is narrower on purpose. I want to focus on what changed when the same cloud-init intent met three different Linux families.
Editor note: Before publishing, add one real Aybars-tested observation here. This topic needs a genuine tested-and-verified signal, such as one specific first-boot difference you reproduced on Raff VMs across Ubuntu, Debian, and Rocky Linux. Your content guide is explicit that this should not be fabricated.
The Important Lesson: “Supports cloud-init” Is Not Specific Enough
The first useful lesson is that “supports cloud-init” is too broad to be operationally helpful.
On paper, Ubuntu, Debian, and Rocky Linux can all participate in the same provisioning model. In practice, the thing that matters to operators is not whether cloud-init exists. It is whether the image behaves cleanly under the exact first-boot sequence your platform expects: user-data processing, key injection, hostname handling, package readiness, metadata access, and network availability.
That difference matters because cloud-init is not a feature you admire in isolation. It is part of a chain. If one link in that chain is slightly off — networking comes up later than expected, package state is older than expected, image identity is not fully cleaned, or the default user behavior is inconsistent — the template can still “work” while creating more uncertainty than it should.
I think that is the right frame for cloud-init testing. The goal is not to prove compatibility. The goal is to remove ambiguity from first boot.
Ubuntu Usually Feels Like the Reference Case
Ubuntu often feels like the baseline many people subconsciously expect cloud-init to match.
That is not because other distributions are worse. It is because Ubuntu cloud images are so common in cloud documentation, examples, and user assumptions that many operators begin to treat Ubuntu behavior as the default shape of cloud-init itself. When something works smoothly there, it feels normal. When another distribution behaves differently, it feels like an exception even if that behavior is technically valid.
That matters in template testing because Ubuntu can hide a bad habit: assuming that a template design proven once on Ubuntu will carry over to Debian or Rocky Linux without friction.
In reality, Ubuntu often becomes the easiest place to build false confidence.
Debian Often Looks Similar Until the Edges Matter
Debian is close enough to Ubuntu that teams often expect a nearly identical first-boot experience. Sometimes that is true. Sometimes it is true only until your assumptions get more specific.
This is where image hygiene, default package state, and the surrounding boot flow start to matter more. If your template depends on a certain package being present, a particular user expectation, or a certain timing assumption around initialization, Debian can expose how Ubuntu-specific your “generic” template really was.
That is not a criticism of Debian. It is exactly why testing matters.
A good cross-distribution cloud-init template should not rely too heavily on implied defaults. The more your provisioning logic depends on what “usually happens,” the more likely you are to discover that one distribution interprets “usually” a little differently than another.
Rocky Linux Changes the Conversation More Than People Expect
Rocky Linux often changes the testing mindset because it pushes the template conversation farther away from Debian-family assumptions.
That is useful.
It forces you to stop thinking only about user-data syntax and start thinking about the entire image context: package ecosystem, boot behavior, network interface expectations, service readiness, and whether the VM still feels predictable once the first cloud-init run has finished.
In other words, Rocky Linux tends to expose whether your cloud-init template is actually cross-platform or simply cross-your-favorite-two-distros.
That is one reason I like including Rocky Linux in template validation even when the expected customer usage is weighted toward Ubuntu. It is a good way to find assumptions that were never as portable as they looked inside the pipeline.
Where First Boot Usually Breaks
The most useful cloud-init failures are rarely dramatic. They are usually small breakpoints that make the VM feel less trustworthy than the template author intended.
Metadata timing and network readiness
If networking does not come up in the order your template expects, cloud-init can still run in a way that feels incomplete or inconsistent. This is especially important when the provisioning flow expects metadata-driven values to be available early and reliably.
SSH key and user assumptions
A cloud-init template that assumes too much about the default user model can become fragile across distributions. This is one of the fastest ways for a template to feel “fine in testing” and then generate first-login confusion later.
Package and service timing
If your first-boot logic expects package operations or service starts to behave identically across distributions, you may be treating the distro family as an implementation detail when it is actually part of the provisioning contract.
Image state that was not cleaned properly
This is one of the quietest causes of unreliable first boot. A template can pass a quick launch test while still carrying identity or initialization state that should not survive image publication. Rocky Linux’s image-builder perspective makes this especially clear: image defaults and generalization are part of reliability, not a cleanup step you can treat as secondary.
The common thread across all of these is simple: first-boot reliability depends on more than cloud-init syntax.
Image Defaults Matter More Than Template Authors Want to Admit
I think this is the most important lesson in the whole topic.
People like to talk about cloud-init as though the template itself is the main variable. In real environments, the underlying image defaults often matter just as much. If the base image is inconsistent, carries stale package assumptions, or boots with different service expectations than your template logic assumes, then the user-data layer ends up taking the blame for problems it did not create on its own.
That is why cloud-init testing belongs next to image quality, not separate from it.
A template is not floating above the operating system. It is landing on a very opinionated starting state. If that starting state differs between Ubuntu, Debian, and Rocky Linux — and it does — then the template author has to decide whether to normalize those differences or design around them explicitly.
The worst option is pretending they are not there.
What We Actually Want From a Reliable Cloud-Init Template
For me, a reliable cloud-init template should do five things well:
- process metadata and user-data without timing surprises
- inject the correct user access path cleanly
- behave predictably on first boot and not only after a reboot
- avoid distro-specific assumptions unless they are declared clearly
- fail in a way that is diagnosable when something goes wrong
That last point matters more than teams admit. You do not need every cloud-init run to be perfect. You do need failures to be understandable. A template that fails transparently is much easier to improve than one that “sort of worked” and left the user with a machine that feels half-initialized.
Why This Changes How I Think About Standardization
This is where the practical value shows up.
A lot of teams think standardization means reducing everything to one template. I think good standardization is more nuanced than that. Sometimes the more reliable strategy is not one universal template across all Linux families. Sometimes it is a shared provisioning intent with distro-aware implementation details.
That approach usually produces fewer false assumptions and a cleaner first-boot experience.
It also fits how real infrastructure evolves. Raff supports multiple operating systems and VM use cases, from Ubuntu and Debian to Rocky Linux, while also giving users platform features like Linux VMs, snapshots, backups, web console access, and private networking. That means reliability is not just about the distro. It is about how the distro, the image, the provisioning model, and the recovery model behave together once the VM is live. The current public product reference also makes it clear that Linux VMs are part of a broader stack that includes snapshots, backups, private networking, and custom OS support, which is exactly why template predictability matters so much in practice.
The more distributions you want to support confidently, the less you can afford to mistake “same YAML” for “same outcome.”
What This Means for You
If you use cloud-init templates across multiple Linux distributions, the right question is not “does cloud-init work here?” The better question is “does first boot behave consistently enough here that I would trust this template in front of a real user?”
That is the standard I would use.
Test your templates across the distributions you actually intend to support, not just the one that was easiest to prototype. Pay close attention to metadata timing, SSH access, package assumptions, and whether the image was generalized properly before publishing. If you are thinking through provisioning models more broadly, start with our guide to cloud-init, custom images, and one-click apps, then pair that with Linux VMs as the practical deployment layer.
That is the real lesson from cross-distro cloud-init testing: reliability does not come from cloud-init alone. It comes from how well the template and the image agree about what first boot is supposed to do.