To install and configure extra PHP modules in this image, first of all drop into the container:
docker exec -t -i nginx /bin/bash
Then configure and install your module:
/usr/local/bin/docker-php-ext-configure sockets
/usr/local/bin/docker-php-ext-install sockets
Now restart php-fpm:
supervisorctl restart php-fpm
We may include a env var to do this in the future.