docker php-fpm user can be configured in .env file

docker/.env

 MARIADB_ROOT_PASSWORD=password
 BOKEH_DATABASE=bokeh
 WEB_PORT=80
-WEB_HOST=localhost
\ No newline at end of file
+WEB_HOST=localhost
+GROUP_ID=1000
+USER_ID=1000
+USERNAME=webmaster

docker/compose.yml

@@ -14,7 +14,12 @@ services:
     image: memcached
 
   php:
-    build: ./php-fpm
+    build:
+      context: ./php-fpm
+      args:
+        - GROUP_ID
+        - USER_ID
+        - USERNAME
     tty: true
     depends_on:
       - db

docker/php-fpm/Dockerfile

@@ -4,6 +4,10 @@ ENV TERM=xterm
 ENV DEBIAN_FRONTEND=noninteractive
 ENV DEBCONF_NONINTERACTIVE_SEEN true
 
+ARG GROUP_ID
+ARG USERNAME
+ARG USER_ID
+
 RUN sed -i 's/main/main contrib non-free/g' /etc/apt/sources.list
 RUN apt-get update && \
     apt-get install -y --no-install-recommends apt-utils apt-transport-https
@@ -67,13 +71,13 @@ RUN docker-php-ext-configure gd --with-freetype --with-jpeg \
 RUN apt-get install -y --no-install-recommends graphviz \
     && apt-get -y autoclean && apt-get -y clean
 
-RUN addgroup --system --gid 1000 webmaster \
-    && adduser --system --home /home/webmaster --shell /bin/bash --disabled-password --gid 1000 --uid 1000 webmaster
+RUN addgroup --gid ${GROUP_ID} ${USERNAME} \
+    && adduser --home /home/${USERNAME} --shell /bin/bash --disabled-password --gid ${GROUP_ID} --uid ${USER_ID} ${USERNAME}
 
 RUN mkdir /usr/local/lib/php/sessions \
     && chmod g-rs /usr/local/lib/php/sessions && chmod o-rx /usr/local/lib/php/sessions \
     && chmod g+wx /usr/local/lib/php/sessions && chmod o+wt /usr/local/lib/php/sessions \
-    && chown webmaster:webmaster /usr/local/lib/php/sessions
+    && chown ${USERNAME}:${USERNAME} /usr/local/lib/php/sessions
 
 RUN wget -O /usr/local/bin/composer https://getcomposer.org/download/latest-stable/composer.phar \
     && chmod +x /usr/local/bin/composer
@@ -109,6 +113,6 @@ EXPOSE 9000
 COPY php.ini /usr/local/etc/php/php.ini
 COPY php-fpm.conf /usr/local/etc/php-fpm.conf
 
-
+RUN sed -i "s:USERNAME:${USERNAME}:" /usr/local/etc/php-fpm.conf
 
 CMD ["php-fpm", "-F"]

docker/php-fpm/php-fpm.conf

@@ -8,7 +8,7 @@ rlimit_core = unlimited
 events.mechanism = epoll
 
 [bokeh]
-user = webmaster
+user = USERNAME
 
 listen = [::]:9000
 listen.mode  = 0666