Add script to create rootfs from Docker container

scripts/rootfs-from-container.sh

@@ -0,0 +1,123 @@
+#!/usr/bin/env bash
+#
+# rootfs-from-container.sh — Create a bootable Wrenn rootfs from a Docker container.
+#
+# Exports a container's filesystem, writes it into an ext4 image, injects
+# envd + wrenn-init, and shrinks the image to minimum size.
+#
+# Usage:
+#   bash scripts/rootfs-from-container.sh <container> <image_name>
+#
+# Arguments:
+#   container   — Docker container name or ID to export
+#   image_name  — Directory name under AGENT_IMAGES_PATH (e.g. "waitlist")
+#
+# Output:
+#   ${AGENT_IMAGES_PATH}/<image_name>/rootfs.ext4
+#
+# Requires: docker, mkfs.ext4, resize2fs, e2fsck, make (for building envd)
+# Sudo is used only for mount/umount/copy-into-image operations.
+
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+PROJECT_ROOT="$(cd "${SCRIPT_DIR}/.." && pwd)"
+AGENT_IMAGES_PATH="${AGENT_IMAGES_PATH:-/var/lib/wrenn/images}"
+
+if [ $# -lt 2 ]; then
+    echo "Usage: $0 <container> <image_name>"
+    exit 1
+fi
+
+CONTAINER="$1"
+IMAGE_NAME="$2"
+OUTPUT_DIR="${AGENT_IMAGES_PATH}/${IMAGE_NAME}"
+OUTPUT_FILE="${OUTPUT_DIR}/rootfs.ext4"
+MOUNT_DIR="/tmp/wrenn-rootfs-build"
+TAR_FILE="/tmp/wrenn-rootfs-export-${IMAGE_NAME}.tar"
+
+# Verify the container exists.
+if ! docker inspect "${CONTAINER}" > /dev/null 2>&1; then
+    echo "ERROR: Container '${CONTAINER}' not found"
+    exit 1
+fi
+
+# Step 1: Build envd.
+echo "==> Building envd..."
+cd "${PROJECT_ROOT}"
+make build-envd
+ENVD_BIN="${PROJECT_ROOT}/builds/envd"
+
+if [ ! -f "${ENVD_BIN}" ]; then
+    echo "ERROR: envd binary not found at ${ENVD_BIN}"
+    exit 1
+fi
+
+if ! file "${ENVD_BIN}" | grep -q "statically linked"; then
+    echo "ERROR: envd is not statically linked!"
+    exit 1
+fi
+
+# Step 2: Export container filesystem.
+echo "==> Exporting container '${CONTAINER}'..."
+docker export "${CONTAINER}" -o "${TAR_FILE}"
+
+cleanup() {
+    echo "==> Cleaning up..."
+    sudo umount "${MOUNT_DIR}" 2>/dev/null || true
+    rmdir "${MOUNT_DIR}" 2>/dev/null || true
+    rm -f "${TAR_FILE}"
+}
+trap cleanup EXIT
+
+# Step 3: Create an oversized ext4 image.
+# Use 2x the tar size + 256MB headroom for filesystem overhead and injected binaries.
+TAR_SIZE_BYTES="$(stat --format=%s "${TAR_FILE}")"
+INITIAL_SIZE_MB=$(( (TAR_SIZE_BYTES / 1024 / 1024) * 2 + 256 ))
+echo "==> Creating ${INITIAL_SIZE_MB}MB ext4 image (will shrink after populating)..."
+sudo mkdir -p "${OUTPUT_DIR}"
+sudo dd if=/dev/zero of="${OUTPUT_FILE}" bs=1M count="${INITIAL_SIZE_MB}" status=progress
+sudo mkfs.ext4 -F "${OUTPUT_FILE}"
+
+# Step 4: Mount and populate.
+echo "==> Mounting image at ${MOUNT_DIR}..."
+mkdir -p "${MOUNT_DIR}"
+sudo mount -o loop "${OUTPUT_FILE}" "${MOUNT_DIR}"
+
+echo "==> Extracting container filesystem..."
+sudo tar xf "${TAR_FILE}" -C "${MOUNT_DIR}"
+
+# Step 5: Inject wrenn guest binaries.
+echo "==> Installing envd..."
+sudo mkdir -p "${MOUNT_DIR}/usr/local/bin"
+sudo cp "${ENVD_BIN}" "${MOUNT_DIR}/usr/local/bin/envd"
+sudo chmod 755 "${MOUNT_DIR}/usr/local/bin/envd"
+
+echo "==> Installing wrenn-init..."
+sudo cp "${PROJECT_ROOT}/images/wrenn-init.sh" "${MOUNT_DIR}/usr/local/bin/wrenn-init"
+sudo chmod 755 "${MOUNT_DIR}/usr/local/bin/wrenn-init"
+
+# Step 6: Verify.
+echo ""
+echo "==> Installed guest binaries:"
+ls -la "${MOUNT_DIR}/usr/local/bin/envd" "${MOUNT_DIR}/usr/local/bin/wrenn-init"
+
+# Unmount before shrinking.
+sudo umount "${MOUNT_DIR}"
+rmdir "${MOUNT_DIR}" 2>/dev/null || true
+
+# Step 7: Shrink the image to minimum size.
+echo ""
+echo "==> Shrinking image..."
+sudo e2fsck -fy "${OUTPUT_FILE}"
+sudo resize2fs -M "${OUTPUT_FILE}"
+
+# Truncate the file to match the shrunk filesystem.
+BLOCK_COUNT="$(sudo dumpe2fs -h "${OUTPUT_FILE}" 2>/dev/null | grep "Block count:" | awk '{print $3}')"
+BLOCK_SIZE="$(sudo dumpe2fs -h "${OUTPUT_FILE}" 2>/dev/null | grep "Block size:" | awk '{print $3}')"
+FS_SIZE_BYTES=$((BLOCK_COUNT * BLOCK_SIZE))
+sudo truncate -s "${FS_SIZE_BYTES}" "${OUTPUT_FILE}"
+
+FINAL_SIZE_MB=$((FS_SIZE_BYTES / 1024 / 1024))
+echo ""
+echo "==> Done. Rootfs created at: ${OUTPUT_FILE} (${FINAL_SIZE_MB}MB)"