fix: Server returns invalid version string causing kubectl/datumctl version parsing failures

[scotwells]

Summary

The milo API server returns an invalid version string v0.0.0-master+$Format:%H$ which causes kubectl and datumctl to fail when querying the server version.

Problem

When running kubectl version or datumctl version against a milo API server:

$ kubectl --kubeconfig .milo/kubeconfig version
Client Version: v1.34.3
Kustomize Version: v5.7.1
Server Version: v0.0.0-master+$Format:%H$
error: server version error: could not parse pre-release/metadata (-master+$Format:%H$) in version "v0.0.0-master+$Format:%H$"

The $Format:%H$ is a git archive substitution placeholder that should be replaced at build time but is being served as a literal string.

Root Cause

The Dockerfile declares ARG variables for version information but never uses them in the go build command:

# Version information is injected via ldflags into k8s.io/component-base/version
ARG VERSION=v0.0.0-master+dev
ARG GIT_COMMIT=unknown
ARG GIT_TREE_STATE=dirty
ARG BUILD_DATE=unknown
RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 \
    go build -trimpath -o milo ./cmd/milo   # <-- No ldflags passed!

Without ldflags, the binary retains the default placeholder values from k8s.io/component-base/version/base.go:

gitVersion   = "v0.0.0-master+$Format:%H$"
gitCommit    = "$Format:%H$"

Proposed Fix

Immediate Fix

Update the Dockerfile to pass ldflags:

RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 \
    go build -trimpath \
    -ldflags="-w -s \
      -X k8s.io/component-base/version.gitVersion=${VERSION} \
      -X k8s.io/component-base/version.gitCommit=${GIT_COMMIT} \
      -X k8s.io/component-base/version.gitTreeState=${GIT_TREE_STATE} \
      -X k8s.io/component-base/version.buildDate=${BUILD_DATE}" \
    -o milo ./cmd/milo

Versioning Strategy Consideration

There's an existing TODO in config.go:299:

// TODO(jreese) better version handling
c.Aggregator.GenericConfig.EffectiveVersion = utilversion.DefaultKubeEffectiveVersion()

The version value itself needs consideration. Options include:

1. Kubernetes-aligned versioning (v1.32.0-milo.0+commit) - Clearly communicates k8s API compatibility
2. Independent milo versioning (v0.1.0+commit) - Requires valid semver
3. Custom EffectiveVersion - Decouple display version from feature gate version

Note: Feature gates use DefaultKubeBinaryVersion (hardcoded to 1.32 in k8s.io/component-base@v0.32.3), so they work correctly regardless of the gitVersion value. The immediate concern is ensuring the version string is valid semver.

Related

• Discovered via datumctl PR: feat: add version command datumctl#114