Use .env file variables during Docker build - docker

Question

I am trying to use the sed command to replace variables during docker build. The variable I am attempting to do (to start) is $DATABASE_HOST. The value for that is coming from my .env file. I am reading online that environment variables are only available during run time if they come from the .env file. Due to this, my sed command is not registering.
Dockerfile:
# Dockerfile for Sphinx SE
# https://hub.docker.com/_/alpine/
FROM alpine:3.12
# https://sphinxsearch.com/blog/
ENV SPHINX_VERSION 3.4.1-efbcc65
# Install dependencies
RUN apk add --no-cache mariadb-connector-c-dev \
postgresql-dev \
wget \
sed
# set up and expose directories
RUN mkdir -pv /opt/sphinx/log /opt/sphinx/index
VOLUME /opt/sphinx/index
# http://sphinxsearch.com/downloads/sphinx-3.3.1-b72d67b-linux-amd64-musl.tar.gz
RUN wget http://sphinxsearch.com/files/sphinx-${SPHINX_VERSION}-linux-amd64-musl.tar.gz -O /tmp/sphinxsearch.tar.gz \
&& cd /opt/sphinx && tar -xf /tmp/sphinxsearch.tar.gz \
&& rm /tmp/sphinxsearch.tar.gz
# point to sphinx binaries
ENV PATH "${PATH}:/opt/sphinx/sphinx-3.4.1/bin"
RUN indexer -v
# redirect logs to stdout
RUN ln -sv /dev/stdout /opt/sphinx/log/query.log \
&& ln -sv /dev/stdout /opt/sphinx/log/searchd.log
# expose TCP port
EXPOSE 36307
EXPOSE 9306
# Copy base sphinx.conf file to container
VOLUME /opt/sphinx/conf
COPY ./sphinx.conf /opt/sphinx/conf/sphinx.conf
# Copy all docker sphinx.conf files
COPY ./configs/web-finder/docker/ /opt/sphinx/conf/
# look for and replace
RUN sed -i "s+DATABASE_HOST+${DATABASE_HOST}+g" /opt/sphinx/conf/sphinx.conf
# Concat the sphinx.conf files for all apps
# RUN cat /tmp/myconfig.append >> /etc/portage/make.conf && rm -f /tmp/myconfig.append
CMD indexer --all --config /opt/sphinx/conf/sphinx.conf \
&& searchd --nodetach --config /opt/sphinx/conf/sphinx.conf
.env file:
DATABASE_HOST=someport
DATABASE_USERNAME=someusername
DATABASE_PASSWORD=somepassword
DATABASE_SCHEMA=someschema
DATABASE_PORT=3306
SPHINX_PORT=36307
sphinx.conf:
searchd
{
listen = 127.0.0.1:$SPHINX_PORT
log = /opt/sphinx/searchd.log
query_log = /opt/sphinx/query.log
read_timeout = 5
max_children = 30
pid_file = /opt/sphinx/searchd.pid
seamless_rotate = 1
preopen_indexes = 1
unlink_old = 1
binlog_path = /opt/sphinx/
}

Answer 1

With sphinx the 'sphinx.conf' file can be 'executable'. Ie it can actully be a 'shell script' (or PHP, perl etc!)
Assuming your .env file makes real (runtime!) environment variables within the container (not overly familiar with Docker), then your sphinx.conf file could be ...
#!/bin/sh
set -eu
cat <<EOF
searchd
{
listen = 127.0.0.1:$SPHINX_PORT
log = /opt/sphinx/searchd.log
query_log = /opt/sphinx/query.log
read_timeout = 5
max_children = 30
pid_file = /opt/sphinx/searchd.pid
seamless_rotate = 1
preopen_indexes = 1
unlink_old = 1
binlog_path = /opt/sphinx/
}
EOF
And because it a shell script, the variables will automatically be expanded :)
Need it executable too!
RUN chmod a+x /opt/sphinx/conf/sphinx.conf
Then dont need the sed command in Dockerfile at all!