Configure: error: mcrypt.h not found. Please reinstall libmcrypt

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Hi guys,

Fairly new to docker and been stuck on this below error for a legacy website whenever I build using docker-compose up -d --build

configure: error: mcrypt.h not found. Please reinstall libmcrypt.

I’ve tried removing mcrypt package from RUN docker-php-ext-install, changing the PHP version. Nothing fixes it.

Found a few answers online saying you need the libmcrypt-dev, which is already included.

docker-compose.yml

version: '3'

services:
  db:
    image: mysql:5
    restart: unless-stopped
    volumes:
      - db_data:/var/lib/mysql
    environment:
      MYSQL_DATABASE: database
      MYSQL_ROOT_PASSWORD: password

  web:
    build: .
    ports:
      - '${HTTP_PORT:-8000}:80'
    restart: unless-stopped
    volumes:
      - ./craft:/var/www/craft
      - ./public:/var/www/public
    depends_on:
      - db

volumes:
  db_data:

Dockerfile

FROM php:5.6-apache-stretch

RUN usermod -u 1000 www-data
RUN groupmod -g 1000 www-data

# Install selected extensions and other stuff
RUN apt-get update \
    && apt-get -y --no-install-recommends install \
        libjpeg-dev \
        libpng-dev \
        mysql-client \
        unzip \
        rsync \
        libmagickwand-dev \
        libmagickcore-dev \
        imagemagick \
        libmcrypt-dev \
        libgeoip-dev \
        libssl1.0.2 \
    && apt-get clean; \
    rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/* /usr/share/doc/*

# pdo and mysql
RUN docker-php-ext-install pdo pdo_mysql mysql mcrypt xmlrpc

# apache mod_rewrite
RUN a2enmod rewrite

# imagemagick
RUN pecl install geoip-1.0.8 imagick-3.4.3 xdebug-2.5.5

# Install Twig C extension
RUN curl -L -o /root/twig.tar.gz https://github.com/twigphp/Twig/archive/v1.24.0.tar.gz && \
    cd /root && \
    tar -zxvf twig.tar.gz && \
    cd /root/Twig-1.24.0/ext/twig && \
    /usr/local/bin/phpize && \
    ./configure --with-php-config=/usr/local/bin/php-config && \
    make  && \
    make install && \
    cd /root && \
    rm -fr /root/CTwig-1.24.0 && \
    rm -fr /root/twig.tgz

WORKDIR /var/www

# change web root (craft expects public)
ENV APACHE_DOCUMENT_ROOT /var/www/public
RUN sed -ri -e 's!/var/www/html!${APACHE_DOCUMENT_ROOT}!g' /etc/apache2/sites-available/*.conf
RUN sed -ri -e 's!/var/www/!${APACHE_DOCUMENT_ROOT}!g' /etc/apache2/apache2.conf /etc/apache2/conf-available/*.conf
RUN echo "LoadModule deflate_module modules/mod_deflate.so" >> /etc/apache2/apache2.conf

# add to apache conf
COPY apache.conf /etc/apache2/conf-available/milesre.conf
RUN a2enconf milesre

# copy php.ini
COPY php.ini /usr/local/etc/php/conf.d/

# Run apache
CMD ["sh", "-c", "chown -R www-data:www-data public craft && apache2-foreground"]