How inject URL while creating flutter build web using docker - flutter

Question

I am trying to inject URL while creating flutter build web. For Inject URL I am using environment variable. Docker file success fully create the docker image and docker container. But when I open web application on browser the environment variable is empty. I did not understand what I am missing. Previously I have no experience with docker That was my first time. Please Guide me what I am doing wrong.
To build docker image I am using command.
docker build . -t test-application
To run docker container I using command
docker run -ti -p 5000:4040 -e API_URL=example.com test-application
My docker file.
# Install dependencies
FROM debian:latest AS build-env
RUN apt-get update
RUN apt-get install -y curl git wget unzip libgconf-2-4 gdb libstdc++6 libglu1-mesa fonts-droid-fallback lib32stdc++6 python3 psmisc
RUN apt-get clean
# Clone the flutter repo
RUN git clone https://github.com/flutter/flutter.git -b stable /usr/local/flutter
# Set flutter path
ENV PATH="/usr/local/flutter/bin:/usr/local/flutter/bin/cache/dart-sdk/bin:${PATH}"
# Enable flutter web
# RUN flutter channel stable
# RUN flutter upgrade
# RUN flutter config --enable-web
# Run flutter doctor
RUN flutter doctor -v
# Copy the app files to the container
COPY . /usr/local/bin/app
# Set the working directory to the app files within the container
WORKDIR /usr/local/bin/app
# Get App Dependencies
RUN flutter clean
# Get App Dependencies
RUN flutter pub get
# Build the app for the web
RUN flutter build web --release --dart-define API_URL=${API_URL:-}
# Document the exposed port
EXPOSE 4040
# Set the server startup script as executable
RUN ["chmod", "+x", "/usr/local/bin/app/server/server.sh"]
# Start the web server
ENTRYPOINT [ "/usr/local/bin/app/server/server.sh" ]
my server.sh file
#!/bin/bash
# Welcome
echo 'Server start script initialized'
# Set the port
PORT=4040
# Kill anything that is already running on that port
echo 'Cleaning port' $PORT
fuser -k 4040/tcp
# Change directories to the release folder
cd build/web/
# Start the server
echo 'Starting server on port' $PORT
python3 -m http.server $PORT
# Exit
echo 'Server exited...'
Getting my environment variable
static const baseUrl =
"${const String.fromEnvironment("API_URL")}/public";

Answer 1

To use a build argument, you need to add an ARG statement in your dockerfile. To also have it available at runtime, you can add an ENV statement, that sets an environment variable with the value of the build argument
# Install dependencies
FROM debian:latest AS build-env
# Add the following two lines
ARG API_URL
ENV API_URL=$API_URL
RUN apt-get update
RUN apt-get install -y curl git wget unzip libgconf-2-4 gdb libstdc++6 libglu1-mesa fonts-droid-fallback lib32stdc++6 python3 psmisc
RUN apt-get clean
# Clone the flutter repo
RUN git clone https://github.com/flutter/flutter.git -b stable /usr/local/flutter
# Set flutter path
ENV PATH="/usr/local/flutter/bin:/usr/local/flutter/bin/cache/dart-sdk/bin:${PATH}"
# Enable flutter web
# RUN flutter channel stable
# RUN flutter upgrade
# RUN flutter config --enable-web
# Run flutter doctor
RUN flutter doctor -v
# Copy the app files to the container
COPY . /usr/local/bin/app
# Set the working directory to the app files within the container
WORKDIR /usr/local/bin/app
# Get App Dependencies
RUN flutter clean
# Get App Dependencies
RUN flutter pub get
# Build the app for the web
RUN flutter build web --release --dart-define API_URL=${API_URL:-}
# Document the exposed port
EXPOSE 4040
# Set the server startup script as executable
RUN ["chmod", "+x", "/usr/local/bin/app/server/server.sh"]
# Start the web server
ENTRYPOINT [ "/usr/local/bin/app/server/server.sh" ]
Then when you build, you add the value you want like this
docker build --build-arg API_URL=example.com -t test-application .
You then don't need to specify it at runtime unless you want to override it, so your run command becomes. Overriding it will only override the environment variable and won't change what was put into the image at build time, of course.
docker run -ti -p 5000:4040 test-application