Can't create connection to Database inside of docker container, host name won't translate

Question

I created an instance of RStudio running inside of a docker container. When working inside of the container, I get the following error when trying to connect to Postgres database: "Error: could not translate host name "ABC-123" to address: Name or service not known".

On my local machine, I execute this step very easily like this:

# Load Libraries
# renv::init()
library(tidyverse)
library(glue)
library(dbplyr)
library(odbc)
library(DBI)
library(RPostgreSQL)
library(sendmailR)
library(paws)
library(config)
library(fs)
# renv::snapshot()


con <- dbConnect(RPostgres::Postgres(), 
                 dbname   = EDP_db, 
                 host     = EDP_host_db, 
                 port     = EDP_db_port, 
                 user     = EDP_db_user, 
                 password = EDP_db_password)

However, inside of the container I get the above mentioned error.

Here is the code for my dockerfile:

FROM rocker/tidyverse:latest

# environment variables
ENV RENV_CONFIG_REPOS_OVERRIDE https://packagemanager.rstudio.com/cran/latest


# Install dependency libraries
RUN apt-get update -qq && apt-get install -y --no-install-recommends \
  build-essential \
  libxml2-dev \
  libcurl4-openssl-dev \
  libicu-dev \
  libsodium-dev \
  libssl-dev \
  libmagick++-dev \
  libudunits2-dev \
  libgdal-dev \
  libgeos-dev \
  libproj-dev \
  lbzip2 \
  libpq-dev \
  make \
  && apt-get clean
  
# expose port on Docker container (Ports that docker opens up) & set working directory
EXPOSE 8787
EXPOSE 5610 # (Port of DB)
EXPOSE 1440
RUN mkdir -p /app
RUN chmod -R 755 /app 
WORKDIR /app/
 

# install R-packages into Docker container
COPY renv.lock renv.lock 
RUN Rscript -e "install.packages('renv', repos = 'http://cran.us.r-project.org')"
RUN Rscript -e "renv::restore()"


# copy necessary files and data into app folder
COPY daily_leads.R /app/daily_leads.R
COPY config.yml /app/config.yml
COPY qk526-rpms-rp-daily-leads.Rproj /app/qk526-rpms-rp-daily-leads-app.Rproj

Lastly, here is the commands that I am using to build the docker image:

docker build -t daily_leads_app:1.0 --build-arg HTTP_PROXY="http://LCPzen.fpl.com:10262" --build-arg HTTPS_PROXY="http://LCPzen.fpl.com:10262" .

docker run --rm -d -p 8787:8787 daily_leads_app:1.0

This is a project for my job, hence the reason for the proxy. I am not sure what type of network that the docker host is configured to use, nor how to configure said network. I have been doing my best to google possible solutions, and the suggestions that seem to be most applicable recommend using a docker compose yaml file to initiate an instance of a postgres database and then make sure the name of the host is the name of the database service you've chosen in docker-compose.yml. However, the database that I am connecting to is a private company database, not something that I can save to my local machine. (Oh, and the error message mentioned above is the copy and pasted error message recieved in the Rstudio console.)