example of installing xdebug inside a docker container

Dockerfile

FROM library/alpine:3.7

ARG DEBUG=false
ARG XDEBUG_VERSION=2.6.0
ARG XDEBUG_VERSION_SHA256=b5264cc03bf68fcbb04b97229f96dca505d7b87ec2fb3bd4249896783d29cbdc
ARG XDEBUG_SOURCE_URL=https://xdebug.org/files

# ( ... ) Install the php

# Compile, install and configure XDebug php extension
ARG XDEBUG_CONFIG_HOST=host.docker.internal
ARG XDEBUG_CONFIG_PORT=9000
ARG XDEBUG_CONFIG_IDEKEY="IDEA_XDEBUG"
RUN set -xe && \
    if [[ "$DEBUG" = "true" ]] ; then \ 
        curl -L -o xdebug-${XDEBUG_VERSION}.tgz ${XDEBUG_SOURCE_URL}/xdebug-${XDEBUG_VERSION}.tgz && \
        if [ -n "XDEBUG_VERSION_SHA256" ]; then \
		    echo "${XDEBUG_VERSION_SHA256}  xdebug-${XDEBUG_VERSION}.tgz" | sha256sum -c - \
	    ; fi && \
        tar -xzf xdebug-${XDEBUG_VERSION}.tgz && \
        cd ./xdebug-${XDEBUG_VERSION} && \
        phpize && \
        sh ./configure --enable-xdebug && \
        make && \
        make install && \
        make clean && \
        cd ../ && \
        echo -e "[XDebug] \n" \
                "zend_extension = $(find /usr/local/lib/php/extensions/ -name xdebug.so) \n" \
                "xdebug.remote_enable = on \n" \
                "xdebug.remote_host = ${XDEBUG_CONFIG_HOST} \n" \
                "xdebug.remote_port = ${XDEBUG_CONFIG_PORT} \n" \
                "xdebug.remote_handler = \"dbgp\" \n" \
                "xdebug.remote_connect_back = off \n" \
                "xdebug.cli_color = on \n" \
                "xdebug.idekey = \"${XDEBUG_CONFIG_IDEKEY}\"" > /usr/local/etc/php/conf.d/xdebug.ini \
    ; fi && \
    unset XDEBUG_CONFIG_HOST \
          XDEBUG_CONFIG_PORT \
          XDEBUG_CONFIG_IDEKEY