R parallel computing and Shiny Server using Dockerfile - r

Question

I need some help with using parallel computing and the package future with shiny inside a Docker container. When I insert my app in shinyapps.io it works normally, but if I use Docker it gives me the following log error.
[2019-04-22T19:49:24.320] [INFO] shiny-server - Shiny Server v1.5.7.890 (Node.js v8.10.0) [2019-04-22T19:49:24.325] [INFO] shiny-server - Using config file "/etc/shiny-server/shiny-server.conf"
[2019-04-22T19:49:24.440] [INFO] shiny-server - Starting listener on 0.0.0.0:80
[2019-04-22T19:49:29.399] [INFO] shiny-server - Created bookmark state directory: /var/lib/shiny-server/bookmarks
[2019-04-22T19:49:29.401] [INFO] shiny-server - Created user bookmark state directory: /var/lib/shiny-server/bookmarks/shiny
[2019-04-22T19:50:30.486] [INFO] shiny-server - Error getting worker: Error: The application took too long to respond.
[2019-04-22T19:50:30.488] [INFO] shiny-server - Error getting worker: Error: The application took too long to respond.
[2019-04-22T19:50:30.489] [INFO] shiny-server - Error getting worker: Error: The application took too long to respond.
My Dockerfile uses R, shiny-server, a connection to Postgres and sqlite. If I don't use the future it works without errors.
# Install R version 3.5
FROM r-base:3.5.1
# Install Ubuntu packages
RUN apt-get update && apt-get install -y \
sudo \
gdebi-core \
pandoc \
pandoc-citeproc \
libcurl4-gnutls-dev \
libcairo2-dev/unstable \
libxt-dev \
libssl-dev \
libpq-dev
# Download and install ShinyServer (latest version)
RUN wget --no-verbose https://s3.amazonaws.com/rstudio-shiny-server-os-build/ubuntu-12.04/x86_64/VERSION -O "version.txt" && \
VERSION=$(cat version.txt) && \
wget --no-verbose "https://s3.amazonaws.com/rstudio-shiny-server-os-build/ubuntu-12.04/x86_64/shiny-server-$VERSION-amd64.deb" -O ss-latest.deb && \
gdebi -n ss-latest.deb && \
rm -f version.txt ss-latest.deb
# Install SQLite
RUN apt-get update && \
DEBIAN_FRONTEND=noninteractive apt-get -yq install sqlite3 && \
rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
# Install R packages that are required
# TODO: add further package if you need!
RUN R -e "install.packages(c('RSQLite', 'RPostgres', 'readxl', 'dplyr', 'lubridate', 'DT', 'billboarder', 'shiny', 'future'), repos='http://cran.rstudio.com/')"
# Copy configuration files into the Docker image
COPY shiny-server.conf /etc/shiny-server/shiny-server.conf
COPY /app /srv/shiny-server/
# Give permission of READWRITE for the SQLite database
RUN chmod a+rw /srv/shiny-server/db/ /srv/shiny-server/db/*
# Make the ShinyApp available at port 80
EXPOSE 80
# Copy further configuration files into the Docker image
COPY shiny-server.sh /usr/bin/shiny-server.sh
CMD ["/usr/bin/shiny-server.sh"]
For an example app I've tried a global.R file loading shiny and future and executing something like
library(shiny)
library(future)
plan(multiprocess)
future({print(1)})
with minimal ui.R (like FluidPage()) and server.R (like server <- function(input, output) {}). My bet are that I'm using Windows 7 environment and that causes a confusion in the multiprocess, if so I can just send the app to my IT right now for them to deploy it on the Linux server, OR it's lacking a linux library or something like that, which I couldn't find out yet. Thank you in advance.