Docker - php-7.0.27-apache soap安装问题

Question

I'm having trouble getting SOAP installed on my php-7.0.27-apache container.We get the following error.

There is E: Package 'php-soap' has no installation candidate as well and returned 100 as exit code.

Here is my Dockerfile -

FROM php:7.0.27-apache

RUN apt-get update \
    && apt-get install -y libpng-dev zlib1g-dev \
    && a2enmod headers \
    && a2enmod rewrite

RUN apt-get install -y libxml2-dev \
                       php-soap

RUN docker-php-ext-install soap