Why is Docker not adding files to my container? - dart

Question

I'm playing around with Google's Dart docker image. I'm trying to build a Hello World app that listens on port 80. I'm running it on Ubuntu Server 14 on Azure.
If I run the google/dart-hello, it all works fine, and I can connect on port 8080.
The google/dart-hello image is based on the google/dart-runtime image, which is in turn, based on google/dart. The base image adds Dart; google/dart-runtime adds a Dockerfile which expects to execute bin/server.dart and expose port 8080, and google/dart-hello supplies the bin/server.dart (and pubspec.yaml) to make it work. google/dart-runtime isn't useful on its own, because it doesn't contain a bin/server.dart or pubspec.yaml.
So, google/dart-runtime is a good base if your server is at bin/server.dart and you want to listen on port 8080. As I want to listen on port 80, I'm using the google/dart image as a base, hoping to squash what's in google/dart-runtime and google/dart-hello into my container, but changed to port 80.
You can find the sources repos for the three Google images here:
google/dart
google/dart-runtime (Dockerfile)
google/dart-hello (Dockerfile)
So, I've taken the Dockerfile from google/dart-runtime and the files from google/dart-hello, so I have the following:
FROM google/dart
WORKDIR /app
ONBUILD ADD pubspec.yaml /app/
ONBUILD ADD pubspec.lock /app/
ONBUILD RUN pub get
ONBUILD ADD . /app
ONBUILD RUN pub get
CMD []
ENTRYPOINT ["/usr/bin/dart", "/app/bin/server.dart"]
EXPOSE 80
In the same directory as this Dockerfile, I have the following files:
bin/server.dart
pubspec.yaml
pubspec.lock
I'm building the image with:
sudo docker build --no-cache -t dart-test .
And here's the output:
danny#linux:~/dart_test$ sudo docker build --no-cache -t dart-test .
Sending build context to Docker daemon 5.632 kB
Sending build context to Docker daemon
Step 0 : FROM google/dart
---> cd92c7fff717
Step 1 : WORKDIR /app
---> Running in d163d2597eba
---> 2802d6769b76
Removing intermediate container d163d2597eba
Step 2 : ONBUILD ADD pubspec.yaml /app/
---> Running in 7b8be2a481c2
---> 096cbe12a2cd
Removing intermediate container 7b8be2a481c2
Step 3 : ONBUILD ADD pubspec.lock /app/
---> Running in 6ae0243b0dee
---> 80f20ebafa87
Removing intermediate container 6ae0243b0dee
Step 4 : ONBUILD RUN pub get
---> Running in 621d4ce5c7f1
---> 89a509d41b11
Removing intermediate container 621d4ce5c7f1
Step 5 : ONBUILD ADD . /app
---> Running in 4de26a33487f
---> b69c65f12441
Removing intermediate container 4de26a33487f
Step 6 : ONBUILD RUN pub get
---> Running in f7cc689f6f81
---> 2ccc79ea6d04
Removing intermediate container f7cc689f6f81
Step 7 : CMD []
---> Running in 10bd31eb6679
---> f828267f00b5
Removing intermediate container 10bd31eb6679
Step 8 : ENTRYPOINT ["/usr/bin/dart", "/app/bin/server.dart"]
---> Running in 013d3ca0f25d
---> a63b59f9fd05
Removing intermediate container 013d3ca0f25d
Step 9 : EXPOSE 80
---> Running in 4301c572e598
---> 75a4317c135c
Removing intermediate container 4301c572e598
Successfully built 75a4317c135c
However, if I try to run this (using sudo docker run --rm -i -t dart-test), I get the following error:
danny#linux:~/dart_test$ sudo docker run -i -t --rm dart-test
Unhandled exception:
Uncaught Error: FileSystemException: Cannot open file, path = '/app/bin/server.dart' (OS Error: No such file or directory, errno = 2)
If I replace the dart execution in the Dockerfile with /bin/bash instead, then when I build and run, I get put into bash at /app/ but the folder is empty.
I've tried this with both the 0.9(?) version and 1.2 (one that came from apt-get docker.io and the other from the more-involved instructions on the Docker website), since I noticed a mention of an ADD fix in the release notes. Both do the same.
I can find lots of info online that people often pipe Dockerfile into STDIN which means there's no context, but you can see in my output that 5KB of data is being sent; though it's possible this is just the Dockerfile and nothing else I guess? They are in the same directory, here's a listing:
danny#linux:~/dart_test$ dir
bin Dockerfile pubspec.lock pubspec.yaml

Answer 1

The ONBUILD instruction is only useful when you create a base image that will be used later by another Dockerfile (see the documentation).
Here because you write the final Dockerfile, you just need to remove the ONBUILD instructions (but keep the raw instructions ADD, RUN, etc).

Answer 2

In your Dockerfile you need to remove the ONBUILD prefixes from your instructions. The ONBUILD prefix is a way to defer execution of certain instructions until this image is referenced by another Dockerfile. Those instructions are stored as part of the metadata for the image that you created but the instructions themselves are not executed until that image is referenced in the FROM field of another Dockerfile.
What you really want is this:
FROM google/dart
WORKDIR /app
ADD pubspec.yaml /app/
ADD pubspec.lock /app/
RUN pub get
ADD . /app
RUN pub get
CMD []
ENTRYPOINT ["/usr/bin/dart", "/app/bin/server.dart"]
EXPOSE 80

Answer 3

The docker image google/dart-runtime is intended to be a base image for your Dart server application. So in your project the Dockerfile should have just the following content
FROM google/dart-runtime
The when you run docker build the ONBUILD commands in the base image will be executed.
If you look at the Dockerfile for google/dart-hello you will see that it has just that one line.