Thanks for writing this article, it helped me a lot.
For a while I couldn’t get things working, but eventually I found a file in my php-fpm docker container config called zz-docker.conf which contains `listen = [::]:9000`. zz-docker.conf is alphabetically high, so was clobbering my other config file, stopping the unix socket communication working. I removed the problem line using this in the Dockerfile using:
sed -i -e ‘/listen/d’ /usr/local/etc/php-fpm.d/zz-docker.conf