# ko — Build and Deploy Go Container Images Without Docker

> A simple container image builder for Go applications that produces minimal images without a Dockerfile or Docker daemon. ko builds your Go binary, layers it onto a distroless base, and pushes to any OCI registry in seconds.

## Install

Save as a script file and run:

# ko — Build and Deploy Go Container Images Without Docker

## Quick Use
```bash
go install github.com/ko-build/ko@latest
export KO_DOCKER_REPO=ghcr.io/myuser
ko build ./cmd/myapp                  # build and push image
ko apply -f deploy.yaml               # build, push, and deploy to K8s
```

## Introduction
ko is a container image builder designed specifically for Go applications. Instead of writing a Dockerfile and running Docker build, you point ko at a Go import path and it compiles the binary, layers it onto a minimal distroless base image, and pushes the result to a registry. Created at Google for Knative development, ko makes Go container workflows dramatically simpler and faster.

## What ko Does
- Builds Go binaries and packages them into OCI container images without Docker
- Pushes images directly to any OCI-compatible container registry
- Resolves image references in Kubernetes YAML and replaces them with built image digests
- Produces minimal distroless images with no shell, package manager, or OS utilities
- Supports multi-platform builds (amd64, arm64) with a single command

## Architecture Overview
ko works entirely in user space without a Docker daemon. It invokes `go build` to compile the target binary for the specified platform, then constructs an OCI image by layering the binary onto a base image (default: `cgr.dev/chainguard/static`). The image layers are computed and pushed directly to the registry using the go-containerregistry library. For Kubernetes workflows, `ko apply` parses YAML files, detects `ko://` image references, builds and pushes them, substitutes the digest, and pipes the result to `kubectl apply`.

## Self-Hosting & Configuration
- Install with `go install github.com/ko-build/ko@latest` or download a release binary
- Set `KO_DOCKER_REPO` to your target registry (e.g., `ghcr.io/myuser`, `gcr.io/myproject`)
- Configure `.ko.yaml` to set default base image, build flags, and platform targets
- Use `ko login` or Docker credential helpers for registry authentication
- Integrate into CI with a single `ko build` step; no Docker-in-Docker needed

## Key Features
- No Dockerfile required: Go import path is the only input needed
- No Docker daemon: builds run entirely in user space with no root or socket access
- Distroless by default: minimal attack surface with no shell or unnecessary packages
- Multi-platform: build linux/amd64 and linux/arm64 images simultaneously
- Kubernetes integration: `ko apply` replaces image refs in YAML with built digests

## Comparison with Similar Tools
- **Docker Build** — General-purpose but requires a Dockerfile and daemon; ko is Go-specific and daemonless
- **Kaniko** — Builds Dockerfiles without a daemon in K8s; ko skips the Dockerfile entirely for Go
- **Buildpacks** — Auto-detects language and builds images; ko is faster and more minimal for Go
- **GoReleaser** — Release automation with Docker support; ko is lighter for just building images
- **Jib** — Similar concept for Java (Maven/Gradle); ko is the Go equivalent

## FAQ
**Q: Does ko only work with Go?**
A: Yes. ko is purpose-built for Go applications. For other languages, consider Buildpacks, Jib (Java), or standard Dockerfiles.

**Q: Can I customize the base image?**
A: Yes. Set `defaultBaseImage` in `.ko.yaml` or use the `--base-image` flag to specify any OCI base image.

**Q: How does ko handle Go build tags and ldflags?**
A: Configure them in `.ko.yaml` under `builds` with `flags`, `env`, and `ldflags` fields, similar to GoReleaser.

**Q: Is ko suitable for production use?**
A: Absolutely. ko is used in production by Knative, Tekton, Sigstore, and many CNCF projects. Its distroless images have a minimal CVE surface.

## Sources
- https://github.com/ko-build/ko
- https://ko.build/docs/

---
Source: https://tokrepo.com/en/workflows/19eb9815-3990-11f1-9bc6-00163e2b0d79
Author: Script Depot