嗨，我正在尝试使用nginx建立容器，但是，在执行以下步骤后，我无法继续操作：

Building nginx
Step 1/17 : FROM nginx:alpine
---> 377c0837328f
Step 2/17 : LABEL maintainer="Mahmoud Zalt mahmoud@zalt.me"
---> Running in 8d53a074e85a
Removing intermediate container 8d53a074e85a
---> 6053f271c802
Step 3/17 : COPY nginx.conf /etc/nginx/
---> ba65da2b9c43
Step 4/17 : ARG CHANGE_SOURCE=false
---> Running in 1d31fc76ab76
Removing intermediate container 1d31fc76ab76
---> 8864e5fb904e
Step 5/17 : RUN if [ ${CHANGE_SOURCE} = true ]; then sed -i 's/dl-cdn.alpinelinux.org/mirrors.aliyun.com/' /etc/apk/repositories ;fi
---> Running in d0f8c3bd67dd
Removing intermediate container d0f8c3bd67dd
---> c6e0c7aaf66f
Step 6/17 : RUN apk update && apk upgrade && apk --update add logrotate && apk add --no-cache openssl && apk add --no-cache bash
---> Running in 37305c5f0e55
fetch http://dl-cdn.alpinelinux.org/alpine/v3.10/main/x86_64/APKINDEX.tar.gz
ERROR: http://dl-cdn.alpinelinux.org/alpine/v3.10/main: network error (check Internet connection and firewall)
WARNING: Ignoring APKINDEX.00740ba1.tar.gz: No such file or directory
fetch http://dl-cdn.alpinelinux.org/alpine/v3.10/community/x86_64/APKINDEX.tar.gz
ERROR: http://dl-cdn.alpinelinux.org/alpine/v3.10/community: network error (check Internet connection and firewall)
WARNING: Ignoring APKINDEX.d8b2a6f4.tar.gz: No such file or directory
2 errors; 36 distinct packages available
ERROR: Service 'nginx' failed to build: The command '/bin/sh -c apk update && apk upgrade && apk --update add logrotate && apk add --no-cache openssl && apk add --no-cache bash' returned a non-zero code: 2

我使用的是Ubuntu 18.04，您能告诉我如何解决吗？