Fix virtual package error

Author: ciarams87

docker/Dockerfile

@@ -15,7 +15,9 @@ RUN --mount=type=secret,id=nginx-repo.crt,dst=/etc/ssl/nginx/nginx-repo.crt,mode
     && apt-get install --no-install-recommends --no-install-suggests -y ca-certificates gnupg curl apt-transport-https \
     && curl -sSL https://cs.nginx.com/static/keys/nginx_signing.key | gpg --dearmor > /etc/apt/trusted.gpg.d/nginx_signing.gpg \
     && curl -sSL -o /etc/apt/apt.conf.d/90pkgs-nginx https://cs.nginx.com/static/files/90pkgs-nginx \
-    && printf "%s\n" "deb https://pkgs.nginx.com/plus/debian buster nginx-plus" > /etc/apt/sources.list.d/nginx-plus.list \
+    && DEBIAN_VERSION=$(awk -F '=' '/^VERSION_CODENAME=/ {print $2}' /etc/os-release) \
+	&& printf "%s\n" "Acquire::https::pkgs.nginx.com::User-Agent \"k8s-ic-$IC_VERSION${BUILD_OS##debian-plus}-apt\";" >> /etc/apt/apt.conf.d/90pkgs-nginx \
+	&& printf "%s\n" "deb https://pkgs.nginx.com/plus/${NGINX_PLUS_VERSION^^}/debian ${DEBIAN_VERSION} nginx-plus" > /etc/apt/sources.list.d/nginx-plus.list \
     && apt-get update && apt-get install -y nginx-plus-${NGINX_PLUS_VERSION} \
     && apt-get remove --purge --auto-remove -y gnupg \
     && rm -rf /var/lib/apt/lists/* \