bug fix、

backend/Dockerfile

@@ -11,26 +11,47 @@ ENV PYTHONUNBUFFERED=1 \
     PIP_DISABLE_PIP_VERSION_CHECK=1 \
     PIP_DEFAULT_TIMEOUT=120
 
-# 替换为阿里云 Debian 镜像源（国内加速）
-RUN sed -i 's/deb.debian.org/mirrors.aliyun.com/g' /etc/apt/sources.list.d/debian.sources && \
-    sed -i 's/security.debian.org/mirrors.aliyun.com/g' /etc/apt/sources.list.d/debian.sources
-
-# 安装系统依赖（含 WeasyPrint 渲染库 + CJK/等宽系统字体）
-RUN apt-get update && apt-get install -y --no-install-recommends \
-    build-essential \
-    default-libmysqlclient-dev \
-    pkg-config \
-    libpango-1.0-0 \
-    libpangoft2-1.0-0 \
-    libpangocairo-1.0-0 \
-    libgdk-pixbuf-2.0-0 \
-    libcairo2 \
-    libffi-dev \
-    shared-mime-info \
-    fontconfig \
-    fonts-dejavu-core \
-    fonts-wqy-microhei \
-    && rm -rf /var/lib/apt/lists/*
+# 优先尝试阿里云 Debian 镜像源，失败时自动回退官方源
+RUN set -eux; \
+    cp /etc/apt/sources.list.d/debian.sources /tmp/debian.sources.bak; \
+    sed -i 's|http://deb.debian.org|http://mirrors.aliyun.com|g' /etc/apt/sources.list.d/debian.sources; \
+    sed -i 's|http://security.debian.org|http://mirrors.aliyun.com|g' /etc/apt/sources.list.d/debian.sources; \
+    if ! apt-get update; then \
+        cp /tmp/debian.sources.bak /etc/apt/sources.list.d/debian.sources; \
+        apt-get update; \
+    fi; \
+    if ! apt-get install -y --no-install-recommends \
+        build-essential \
+        default-libmysqlclient-dev \
+        pkg-config \
+        libpango-1.0-0 \
+        libpangoft2-1.0-0 \
+        libpangocairo-1.0-0 \
+        libgdk-pixbuf-2.0-0 \
+        libcairo2 \
+        libffi-dev \
+        shared-mime-info \
+        fontconfig \
+        fonts-dejavu-core \
+        fonts-wqy-microhei; then \
+        cp /tmp/debian.sources.bak /etc/apt/sources.list.d/debian.sources; \
+        apt-get update; \
+        apt-get install -y --no-install-recommends \
+            build-essential \
+            default-libmysqlclient-dev \
+            pkg-config \
+            libpango-1.0-0 \
+            libpangoft2-1.0-0 \
+            libpangocairo-1.0-0 \
+            libgdk-pixbuf-2.0-0 \
+            libcairo2 \
+            libffi-dev \
+            shared-mime-info \
+            fontconfig \
+            fonts-dejavu-core \
+            fonts-wqy-microhei; \
+    fi; \
+    rm -rf /var/lib/apt/lists/*
 
 # 复制依赖文件
 COPY requirements.txt .