Exclude path at Docker image build time to improve size - docker

Question

In our project, we have an ASP.NET Core project with an Angular2 client. At Docker build time, we launch:
FROM microsoft/dotnet:latest
COPY . /app
WORKDIR /app
RUN ["dotnet", "restore"]
RUN apt-get -qq update ; apt-get -qqy --no-install-recommends install \
git \
unzip
RUN curl -sL https://deb.nodesource.com/setup_7.x | bash -
RUN apt-get install -y nodejs build-essential
RUN ["dotnet", "restore"]
RUN npm install
RUN npm run build:prod
RUN ["dotnet", "build"]
EXPOSE 5000/tcp
ENV ASPNETCORE_URLS http://*:5000
ENTRYPOINT ["dotnet", "run"]
Since restoring the npm packages is essential to be able to build the Angular2 client using npm run build, our Docker image is HUGE, I mean almost 2GB. Built Angular2 client is only 1.7Mb itself.
Our app does nothing fancy: simple web API writing to MongoDB and displaying static files.
In order to improve the size of our image, is there any way to exclude path which are useless at run time? For example node_modules or any .NET Core source?

Answer 1

Dotnet may restore much, especially if you have multiple targets platforms (linux, mac, windows).
Depending on how your application is configured (i.e. as portable .NET Core app or as self-contained), it can also pull the whole .NET Core Framework for one, or multiple platforms and/or architectures (x64, x86). This is mainly explained here.
When "Microsoft.NETCore.App" : "1.0.0" is defined, without the type platform, then then complete framework will be fetched via nuget. Then if you have multiple runtimes defined
"runtimes": {
"win10-x64": {},
"win10-x86": {},
"osx.10.10-x86": {},
"osx.10.10-x64": {}
}
it will get native libraries for all this platforms too. But not only in your project directory but also in ~/.nuget and npm-cache additionally to node_modules in your project + eventual copies in your wwwdata.
However, this is not how docker works. Everything you execute inside the Dockerfile is written to the virtual filesystem of the container! That's why you see this issues.
You should follow my previous comment on your other question:
Run dotnet restore, dotne build and dotnet publish outside the Dockerfile, for example in a bash or powershell/batch script.
Once finished call copy the content of the publish folder in your container with
dotnet publish
docker build bin\Debug\netcoreapp1.0\publish ... (your other parameters here)
This will generate publish files on your file system, only containing the required dll files, Views and wwwroot content without all the other build files, artifacts, caches or source and will run the docker process from the bin\Debug\netcoreapp1.0\publish folder.
You also need to change your docker files, to copy the files instead of running the commands you have during container building.
Scott uses this Dockerfile for his example in his blog:
FROM ... # Your base image here
ENTRYPOINT ["dotnet", "YourWebAppName.dll"] # Application to run
ARG source=. # An argument from outside, here store the path from real filesystem
WORKDIR /app
ENV ASPNETCORE_URLS http://+:82 # Define the port it should listen
EXPOSE 82
COPY $source . # copy the files from defined folder, here bin\Debug\netcoreapp1.0\publish to inside the docker container
This is the recommended approach for building docker containers. When you run the build commands inside, all the build and publish artifacts remain in the virtual file system and the docker image grows unexpectedly.