Using xdebug through Docker container in PhpStorm

I've read some posts about this but none helped in my case or simply overlooked the missing piece.

I cannot get xdebug to work on PhpStorm using a Docker container.

Docker-compose.yml

version: '2'

services:
  web:
    image: nginx:latest
    volumes:
    - .:/usr/share/nginx/html
    - ./nginx/nginx.conf:/etc/nginx/nginx.conf
    - ./nginx/logs:/var/logs/nginx
    - ./nginx/site-enabled/default.conf:/etc/nginx/sites-enabled/default.conf
    ports:
    - "80:80"
    depends_on:
    - php

  db:
    image: mysql:5.7
    environment:
      MYSQL_ROOT_PASSWORD: 1234
      MYSQL_DATABASE: local_db
      MYSQL_USER: root
      MYSQL_PASSWORD: 1234
    ports:
    - "3306:3306"

  php:
    build: images/php
    volumes:
    - .:/usr/share/nginx/html
    - ./config/docker/php/php.ini:/usr/local/etc/php/php.ini
    - ./config/docker/php/ext-xdebug.ini:/usr/local/etc/php/conf.d/ext-xdebug.ini
    - ./config/docker/php/php-fpm.conf:/usr/local/etc/php-fpm.conf
    user: www-data
    depends_on:
    - db

config/docker/php/ext-xdebug.ini

zend_extension="/usr/lib/php7/xdebug.so"
xdebug.remote_enable=1
xdebug.remote_port=9000
xdebug.overload_var_dump=1
xdebug.default_enable=1
xdebug.remote_autostart=1
xdebug.idekey=PHPSTORM
xdebug.remote_connect_back=1
xdebug.remote_host=172.20.0.1 # ip of host inside docker container
xdebug.remote_log=/usr/share/nginx/html/xdebug.log

error from xdebug.log

Log opened at 2017-05-31 11:01:14
I: Checking remote connect back address.
I: Checking header 'HTTP_X_FORWARDED_FOR'.
I: Checking header 'REMOTE_ADDR'.
I: Remote address found, connecting to 172.20.0.1:9000.
W: Creating socket for '172.20.0.1:9000', poll success, but error: Operation now in progress (29).
E: Could not connect to client. :-(
Log closed at 2017-05-31 11:01:14

In PhpStorm I'm using remote debugger with following settings:

server

Host - 127.0.0.1  
Port - 80 

Absolute path on server

/usr/share/nginx/html

IDE session key

PHPSTORM