Sometimes when using data volumes (-v flags) permissions issues can arise between the host OS and the container. We avoid this issue by allowing you to specify the user PUID and optionally the group PGID. Ensure the data volume directory on the host is owned by the same user you specify and it will "just work" ™.
An example of mapping the UID and GID to the container is as follows:
docker run -d -e "PUID=`id -u $USER`" -e "PGID=`id -g $USER`" -v local_dir:/var/www/html jcsofts/alpine-nginx-php7:latest
This will pull your local UID/GID and map it into the container so you can edit on your host machine and the code will still run in the container.