These are helper scripts that helps one install php extensions from source

• not all extensions are available in a distribution native package manager or pecl
• even if these exist one may want to configure these differently or optimize

Talking about the scripts

• docker-php-ext-configure - configure an extension before you build it with docker-php-ext-install. It's executed by docker-php-ext-install, so one should use it if wants to override the defaults
• docker-php-ext-install - build extension from source, usually executes docker-php-ext-configure for build configuration, enables the extension (php.ini entry) by executing docker-php-ext-enable after all
• docker-php-ext-enable - enables an already installed extension by adding a specific entry to php.ini. Extensions installed with pecl or native package managers may not be enabled by default thus require this additional step. As mentioned above, extensions installed with docker-php-ext-install are being enabled automatically.

I had the same problem a while ago. I started a container and typed the ext-install command into this container. Once I found all the dependencies, I wrote them into the Dockerfile.

Example:

RUN apt-get update && apt-get install -y \
libmcrypt-dev \
&& docker-php-ext-install -j$(nproc) mcrypt

There is a dependency that libmcrypt-dev needed before you can run docker-php-ext-install mcrypt

I've checked my older Dockerfiles and found something which might help you

FROM php:5.6-apache

RUN apt-get update && apt-get install -y \
        libfreetype6-dev \
        libjpeg62-turbo-dev \
        libmcrypt-dev \
        libpng12-dev \
    libicu-dev \
     libxml2-dev \
    vim \
        wget \
        unzip \
        git \
    && docker-php-ext-install -j$(nproc) iconv intl xml soap mcrypt opcache pdo pdo_mysql mysqli mbstring \
    && docker-php-ext-configure gd --with-freetype-dir=/usr/include/ --with-jpeg-dir=/usr/include/ \
    && docker-php-ext-install -j$(nproc) gd

RUN a2enmod rewrite && mkdir /composer-setup && wget https://getcomposer.org/installer -P /composer-setup && php /composer-setup/installer --install-dir=/usr/bin && rm -Rf /composer-setup && curl -LsS https://symfony.com/installer -o /usr/local/bin/symfony && chmod a+x /usr/local/bin/symfony
# Create symlink for default conf
RUN ln -s /etc/apache2/sites-available/000-default.conf /etc/apache2/sites-enabled/000-default.conf && mkdir /composer-setup && wget https://getcomposer.org/installer -P /composer-setup && php /composer-setup/installer --install-dir=/usr/bin && rm -Rf /composer-setup && curl -LsS https://symfony.com/installer -o /usr/local/bin/symfony && chmod a+x /usr/local/bin/symfony

New solution

You need to create new Dockerfile for specific service, in this case php:

php/Dockerfile

FROM php:7.1.1-fpm
RUN apt -yqq update
RUN apt -yqq install libxml2-dev
RUN docker-php-ext-install pdo_mysql
RUN docker-php-ext-install xml

And then link to it in your docker-compose.yml file, just like this:

services:
  // other services
  php:
    build: ./php
    ports:
      - "9000:9000"
    volumes:
      - .:/dogopic
    links:
      - mariadb

Please look at build parameter - it points to directory in which is that new Dockerfile located.

Old solution

I walked around the problem. I've figured out that I can still run this docker-php-ext-install script using following command:

docker-compose exec <your-php-container> docker-php-ext-install pdo pdo_mysql mbstring

And because of the convenience I've created this simple Batch file to simplify composing containers just to one command: ./docker.bat

@ECHO OFF

docker-compose build
docker-compose exec php docker-php-ext-install pdo pdo_mysql mbstring
docker-compose up