Docker install memcached
The PECL memcached package introduced the dependency on PHP 7 in version 3.0.0. You can still install the 2.x version of that package:
FROM php:5-apacheRUN apt-get update && apt-get install -y libmemcached11 libmemcachedutil2 build-essential libmemcached-dev libz-devRUN pecl install memcached-2.2.0RUN echo extension=memcached.so >> /usr/local/etc/php/conf.d/memcached.ini