Dockerfile
FROM php:7.4-cli-alpine
RUN apk add gnu-libiconv --update-cache --repository http://dl-cdn.alpinelinux.org/alpine/edge/testing/ --allow-untrusted
ENV LD_PRELOAD /usr/lib/preloadable_libiconv.so php
# install composer
RUN curl -sS https://getcomposer.org/installer | php -- --install-dir=/usr/local/bin --filename=composer