test(interop): let the MinIO fixture lab build from registry mirrors (#6148)

crates/rio-v2/tests/minio_fixture_lab/Dockerfile

@@ -6,9 +6,18 @@
 #
 # The MinIO release is pinned so the captured fixture format is reproducible;
 # this is the release the interop tests were validated against.
-FROM minio/minio:RELEASE.2025-09-07T16-13-09Z AS minio
+#
+# Both base images are build args so a network that cannot reach Docker Hub can
+# point them at a mirror carrying the same content — quay.io publishes the MinIO
+# releases, and public.ecr.aws mirrors the official Python images. CI keeps the
+# Docker Hub defaults. Override with:
+#   --build-arg MINIO_IMAGE=quay.io/minio/minio:RELEASE.2025-09-07T16-13-09Z \
+#   --build-arg PYTHON_IMAGE=public.ecr.aws/docker/library/python:3.12-slim
+ARG MINIO_IMAGE=minio/minio:RELEASE.2025-09-07T16-13-09Z
+ARG PYTHON_IMAGE=python:3.12-slim
+FROM ${MINIO_IMAGE} AS minio
 
-FROM python:3.12-slim
+FROM ${PYTHON_IMAGE}
 RUN apt-get update \
     && apt-get install -y --no-install-recommends openssl ca-certificates \
     && rm -rf /var/lib/apt/lists/*

crates/rio-v2/tests/minio_fixture_lab/README.md

@@ -22,6 +22,18 @@ Use the automated path when you want the lab to:
 - upload a predefined SSE fixture case
 - export the generated backend tree into the lab layout
 
+## Networks without Docker Hub access
+
+`capture_via_docker.sh` pulls its two base images from Docker Hub by default. Where that registry is unreachable, point the build at mirrors carrying the same content — quay.io publishes the MinIO releases and public.ecr.aws mirrors the official Python images:
+
+```bash
+MINIO_LAB_MINIO_IMAGE=quay.io/minio/minio:RELEASE.2025-09-07T16-13-09Z \
+MINIO_LAB_PYTHON_IMAGE=public.ecr.aws/docker/library/python:3.12-slim \
+./capture_via_docker.sh
+```
+
+Pin the MinIO tag to the same release the Dockerfile names; an unpinned `:latest` captures whatever format that day's build writes, which is not what the interop tests were validated against.
+
 ## Layout
 
 The default root is `artifacts/minio-fixture-lab`, which is already ignored by the repository.

crates/rio-v2/tests/minio_fixture_lab/capture_via_docker.sh

@@ -34,8 +34,19 @@ if [ "${cases[0]}" != "all" ]; then
   done
 fi
 
+# Base images are overridable so a network without Docker Hub access can point
+# them at a mirror (see the Dockerfile header). Unset by default, which keeps the
+# Dockerfile's Docker Hub defaults for CI.
+build_args=()
+if [ -n "${MINIO_LAB_MINIO_IMAGE:-}" ]; then
+  build_args+=(--build-arg "MINIO_IMAGE=${MINIO_LAB_MINIO_IMAGE}")
+fi
+if [ -n "${MINIO_LAB_PYTHON_IMAGE:-}" ]; then
+  build_args+=(--build-arg "PYTHON_IMAGE=${MINIO_LAB_PYTHON_IMAGE}")
+fi
+
 echo ">> building ${IMAGE}"
-docker build -f "${SCRIPT_DIR}/Dockerfile" -t "${IMAGE}" "${SCRIPT_DIR}"
+docker build -f "${SCRIPT_DIR}/Dockerfile" -t "${IMAGE}" "${build_args[@]}" "${SCRIPT_DIR}"
 
 echo ">> capturing fixtures into ${FIXTURE_REL}"
 docker run --rm -v "${REPO_ROOT}:/repo" "${IMAGE}" \