Comparison of Kaniko, Buildah, and Podman in High-Security CI/CD Environments

Short answer: No, you can’t use Buildah/Podman everywhere you use Kaniko — they’re different enough in runtime and security model that you’ll hit some blockers in high-security environments.Here’s the breakdown:

1. Execution Model Differences

Tool	Container Runtime Dependency	Root/Privileged Needed?	Common Deployment Pattern
Kaniko	None (runs in any OCI-compatible container runtime, e.g. Docker, containerd)	No root, no privileged mode	Runs in Kubernetes Pod without special privileges
Buildah	Usually runs on the host or in a container with privileged mode	Needs `CAP_SYS_ADMIN` or full privileged container to do overlayfs mounts	Best on a dedicated build node or OpenShift Build pods
Podman	Can run rootless on a Linux host, but in Kubernetes it’s tricky	Rootless Podman inside a pod is possible but requires user namespaces + correct cgroups config (not common)	Often used in VM or bare-metal CI runners, not in restricted k8s pods

2. Security Constraints

Kaniko is designed for unprivileged Kubernetes builds:
No need for --privileged or root.
Can build from scratch and push to registries without touching the host’s container runtime.
Buildah/Podman:
Rootless mode exists, but rootless containers in Kubernetes are rare in shared CI due to user namespace isolation requirements.
In rootful mode they require privileged pods or CAP_SYS_ADMIN (security policies often forbid both).
Buildah’s default storage driver (overlay) needs a writable /var/lib/containers with special mounts; this isn’t available in hardened clusters without privileged mounts.
Podman in rootless mode often needs fuse-overlayfs and slirp4netns, which aren’t standard in stripped-down container images.

3. Where Each Fits

Kaniko → Kubernetes-native, works in most high-security CI/CD (GitLab, Tekton, Argo Workflows, etc.) without elevated privileges.
Buildah → Great in OpenShift (because OpenShift sets up user namespaces and mounts properly), or in dedicated VM/host-based CI runners.
Podman → Nice for developer machines, local rootless builds, and secure single-host CI runners — but not a drop-in Kaniko replacement inside arbitrary k8s pods.

4. If You Try to Replace Kaniko

To run Buildah/Podman in the same environments as Kaniko without root:

You’d need:
Kubernetes cluster with user namespace support enabled.
Properly configured fuse-overlayfs in the image.
Writable storage that works without privileged mounts.
In practice, these aren’t usually enabled in “high-security” or multi-tenant clusters.

✅ Bottom line:

Kaniko is the safest bet for unprivileged Kubernetes builds.
Buildah/Podman are more flexible in local or VM builds, but generally require privileges that Kaniko does not unless your platform is specifically designed for rootless Podman/Buildah (e.g., OpenShift).

If you want, I can map exactly which CI/CD runners and environments support Buildah/Podman rootless today so you can see where you can and can’t drop them in for Kaniko. That’s where the subtle “gotchas” live.