Beyond Docker: Exploring Modern Container Engines and Build Tools

Why Look Beyond Docker?

Docker was the sole container platform in its early days, but today it is just one of many OCI‑compatible engines. Because Docker tries to cover every container‑related task in a single monolithic tool, dedicated utilities that excel at a single function often provide better performance, security, or flexibility.

Container Engines

Container engines provide the user interface for pulling images, creating container file‑systems, and delegating execution to a runtime. The most prominent Docker alternative is Podman , which runs without a daemon and does not require root privileges. Podman also supports pods—the smallest Kubernetes compute unit—making migration to Kubernetes straightforward.

~ $ podman pod create --name mypod
~ $ podman pod list

POD ID   NAME   STATUS   CREATED          # OF CONTAINERS   INFRA ID
211eaecd307b   mypod   Running   2 minutes ago   1   a901868616a5

~ $ podman run -d --pod mypod nginx   # First container
~ $ podman run -d --pod mypod nginx   # Second container
~ $ podman ps -a --pod

CONTAINER ID   IMAGE                         COMMAND   CREATED          STATUS          PORTS   NAMES          POD          POD NAME
3b27d9eaa35c   docker.io/library/nginx:latest   nginx -g daemon off...   2 seconds ago   Up 1 second ago          brave_ritchie   211eaecd307b   mypod
...

Podman’s CLI mirrors Docker’s, so an alias docker=podman can make the switch seamless. Other engines such as LXD, CRI‑O, and rkt exist, but they are either niche or no longer actively maintained.

Image‑Build Tools

While Docker’s docker build remains common, several alternatives provide daemon‑less builds and finer‑grained control.

Buildah (Red Hat) works hand‑in‑hand with Podman. It can build from a Dockerfile or Containerfile without a daemon, offering layer‑by‑layer manipulation.

Kaniko runs inside a container and is designed for building images inside Kubernetes clusters, avoiding the need for a local Docker daemon.

BuildKit is the next‑generation Docker build engine, enabling parallel builds, cache reuse, and rootless operation, though it still requires the buildkitd daemon.

Other niche tools include S2I (source‑to‑image for OpenShift), Jib (Java images via Maven/Gradle), and Bazel (full build system with rules_docker).

~ $ buildah bud -f Dockerfile .
~ $ buildah from alpine:latest   # equivalent to FROM alpine:latest
~ $ buildah run alpine-working-container -- apk add --update --no-cache python3
~ $ buildah commit alpine-working-container my-final-image

REPOSITORY          TAG      IMAGE ID        CREATED          SIZE
localhost/my-final-image   latest   1ff90ec2e26   22 seconds ago   51.4 MB

Container Runtimes

The runtime executes containers according to the OCI spec. The most widely used is runC , which underpins Docker, Podman, and CRI‑O. Crun is a Red Hat‑maintained, C‑based alternative offering better performance and memory efficiency.

CRI‑O is not an engine but a runtime focused on Kubernetes; it delegates to runC and is typically used only on cluster nodes. containerd , a CNCF graduated project, acts as a daemon that manages image storage and runtime interaction, serving as Docker’s default runtime and a common choice for Kubernetes deployments.

Image Inspection and Distribution

Beyond docker inspect, tools like Skopeo enable remote image inspection and copy operations without pulling images locally, facilitating cross‑registry migrations. Dive provides a user‑friendly analysis of image layers, size, and efficiency, useful for CI pipelines.

Conclusion

The goal is not to force the abandonment of Docker but to present the full landscape of container engines, build utilities, runtimes, and distribution tools. Each option has strengths and trade‑offs; selecting the right combination depends on your workflow, security requirements, and target environments.