How to set laravel file permissions inside a docker image - laravel

Question

I have the following dockerfile to build my Laravel web application. After I run it I get permission errors when trying to acccess the vendor and storage directories. My question is what is the correct way of setting permissions for Laravel for a php:7.2-fpm base image. The error I receive is:
fopen(/var/www/app/vendor/dompdf/dompdf/lib/fonts/glyphicons-halflings-normal_4ced20531a4f462a8c5c535d4debd2eb.ufm):
failed to open stream: Permission denied
Dockerfile
FROM php:7.2-fpm
WORKDIR /var/www/app
RUN apt-get update && apt-get install -y \
build-essential \
libpng-dev \
libjpeg62-turbo-dev \
libfreetype6-dev \
locales \
zip \
jpegoptim optipng pngquant gifsicle \
vim \
unzip \
git \
curl \
npm
RUN curl -sL https://deb.nodesource.com/setup_9.x | bash
RUN apt-get install -y nodejs
# Clear cache
RUN apt-get clean && rm -rf /var/lib/apt/lists/*
# Install extensions
RUN docker-php-ext-install pdo_mysql mbstring zip exif pcntl
RUN docker-php-ext-configure gd --with-gd --with-freetype-dir=/usr/include/ --with-jpeg-dir=/usr/include/ --with-png-dir=/usr/include/
RUN docker-php-ext-install gd
RUN docker-php-ext-install bcmath
# Install composer
RUN curl -sS https://getcomposer.org/installer | php -- --install-dir=/usr/local/bin --filename=composer
# Copy existing application directory contents
COPY . /var/www/app
RUN chmod -R 775 /var/www/app
RUN chmod -R 775 /var/www/app/vendor
RUN chmod -R 777 /var/www/app/storage
# COPY --from=nodeBuild ./ /var/www
RUN composer install
RUN npm install
RUN npm update
# Expose port 9000 and start php-fpm server
EXPOSE 9000
CMD ["php-fpm"]

Answer 1

I removed these commands:
RUN chmod -R 775 /var/www/app
RUN chmod -R 775 /var/www/app/vendor
RUN chmod -R 777 /var/www/app/storage
I got the webserver to own the directory recursively:
chown -R www-data:www-data /var/www
This resolved the problem