ERROR: unsatisfiable constraints about dockerwordpress HOT 3 OPEN

I inserted 'apk update ' in the Dockerfile. This does the trick for me.
# We need these system-level scritps to run WordPress successfully RUN apk update \ apk add --no-cache nginx mysql-client supervisor curl \ bash redis imagemagick-dev libpng-dev curl-dev libxml2-dev

from dockerwordpress.

I have the same problem. apk update didn't do a trick, I mean it does for this step, but it fails later on - I've got this error message:
configure: error: png.h not found. ERROR: Service 'wordpress' failed to build: The command '/bin/sh -c apk add --no-cache libtool build-base autoconf && docker-php-ext-install -j$(grep -c ^processor /proc/cpuinfo 2>/dev/null || 1) iconv gd mbstring fileinfo curl xmlreader xmlwriter spl ftp mysqli opcache && pecl install imagick && docker-php-ext-enable imagick && apk del libtool build-base autoconf' returned a non-zero code: 1

from dockerwordpress.

After changeing the Dockerfile as follows it works for me on Debian 9 as docker host.
To find out which package should be installed have look to https://pkgs.alpinelinux.org/packages and search for -dev packages like *ssh*-dev

FROM php:7.0.6-fpm-alpine
MAINTAINER Tomaz Zaman <[email protected]>

# We need these system-level scritps to run WordPress successfully
RUN apk --repository http://dl-3.alpinelinux.org/alpine/v3.6/community/ \
        --repository http://dl-3.alpinelinux.org/alpine/v3.6/main/ \
        --update \
    add --no-cache nginx mysql-client supervisor curl \
    bash redis imagemagick-dev libpng-dev curl-dev libxml2-dev libssh2-dev

# As per image documentation, this is how we install PHP modules
RUN docker-php-ext-install -j$(grep -c ^processor /proc/cpuinfo 2>/dev/null || 1) \
            iconv gd mbstring fileinfo curl xmlreader xmlwriter spl ftp mysqli opcache

# Install imagemagick for PHP
RUN apk --repository http://dl-3.alpinelinux.org/alpine/v3.6/community/ \
        --repository http://dl-3.alpinelinux.org/alpine/v3.6/main/ \
    add --no-cache libtool build-base autoconf \
    && pecl install imagick \
    && docker-php-ext-enable imagick \
    && apk del libtool build-base autoconf

from dockerwordpress.