Scarab field test #019 fixes Docker Compose variable discovery boundary

── What shipped ──

Scarab Systems opened a public branch on the Docker Compose repo and merged a patch that skips validation when loading the unresolved model for variable discovery [GitHub Issue]. The field test is described on dev.to [dev.to]. The issue arose in #13613 when Compose validated a templated port field such as host_ip: "${LXKNS_ADDRESS:-127.0.0.1}" and reported “invalid IP address” before interpolation. The patch separates discovery and validation: variable discovery now inspects the raw model, while validation runs only after interpolation. Regression tests for host_ip and published fields were added, and go test ./cmd/compose and docker buildx bake lint both pass with zero issues. The change lands in the scarab-systems/compose public branch and is slated for the next Docker Compose release.

── Why it matters ──

• False positives disappear: templated Compose files no longer trigger spurious IP errors, eliminating work‑arounds.
• CI pipelines stay fast: preventing premature validation removes the need for separate lint steps that strip interpolation syntax, streamlining builds for large microservice fleets.
• The boundary model sets a precedent: separating discovery and validation can be adopted by other config tools such as Helm and Kustomize, reducing timing‑related bugs across the container‑orchestration ecosystem.

── Editor's take ──

Separating discovery from validation is a pragmatic design choice that prevents misleading errors and keeps the validation contract intact. Scarab’s narrowly scoped patch, coupled with added regression coverage, shows how to fix timing bugs without weakening overall validation guarantees.

── Reader poll ──

Which config templating approach do you trust for production deployments?

• Docker Compose variable discovery
• Helm chart templating
• Kustomize overlay generation