Cannot run or deploy a Dart application with a git dependency to a private repo

[GoogleCodeExporter]

If a Dart application contains a pubspec.yaml file which declares a Git 
dependency to a private repository, e.g.:

  my_package:
    git: url: git@github.com:myuser/mypackage.git

...and we try to run the app:

  gcloud --verbosity debug preview app run app.yaml

...gcloud fails with error:

Git error. Command: git clone --mirror git@github.com:myuser/mypackage.git 
/root/.pub-cache/git/cache/notary-6166e308f1b9a5023d5efb5c1d0ceed6e31d7eac
error: cannot run ssh: No such file or directory
fatal: unable to fork

Original issue reported on code.google.com by cristian...@gmail.com on 20 Nov 2014 at 10:01

[GoogleCodeExporter]

This is caused by a sad Docker limitation.

see also:
- http://stackoverflow.com/questions/26883460
- http://superuser.com/questions/842642
- https://github.com/docker/docker/issues/1676
- https://github.com/docker/docker/issues/6094

Original comment by gzoe...@gmail.com on 21 Nov 2014 at 5:08

[GoogleCodeExporter]

Simple Dart apps can be deployed to custom runtimes on Managed VMs following 
the examples at https://www.dartlang.org/cloud/. However many serious, 
larger-scale projects depend on local packages and private source repositories.

The Dart pub package manager supports referencing both local packages and 
Github repos in pubspec.yaml and the apps run just fine, however running or 
deploying such apps using the gcloud utility of the Google Cloud SDK is not 
possible.

This particular issue is about referencing private Gitbub repos from Dart 
projects. Perhaps another issue should be created for supporting local packages.

Specifically, the error message references a problem with executing ssh. It 
seems that if it is possible to reference packages from 
https://pub.dartlang.org/ that are downloaded and deployed when running the 
command, it should also be possible to reference Git repositories. There seems 
to be no difference beyond the transfer protocols used.

Original comment by cristian...@gmail.com on 21 Nov 2014 at 6:30

[GoogleCodeExporter]

Here is a nice workaround for Linux (don't know if other OS support similar 
workarounds)
http://superuser.com/questions/842642

I also think that "gcloud preview app run" should just mount the context 
directory as a volume instead of building a Docker image each time a source 
file changes.

Original comment by gzoe...@gmail.com on 23 Nov 2014 at 11:16

[GoogleCodeExporter]

@christian

One possible way to work around the ssh login issue is to instead checkout the 
git repository as a local package directory and deploy it as part of your 
application.
To do this you would use the dart-runtime-base dockerfile as your parent docker 
image and refer to the package as a local package using a path in the 
pubspec.yaml file.
You can see how to on 
https://github.com/dart-lang/dart_docker/tree/master/runtime-base under the 
Usage.

This way you avoid having to ship you git credentials with your docker image 
and instead ship the (granted larger) repository as part of the application 
docker image.
To avoid shipping more than necessary you can also add a .dockerignore file to 
your docker app directory to exclude the directories and files you don't want 
to package up as part of your image. See 
http://docs.docker.com/reference/builder/#the-dockerignore-file for more 
details.

Original comment by wibl...@google.com on 12 Jan 2015 at 9:02

[GoogleCodeExporter]

@christian

Being a bit more elaborate I see the following (currently working) ways of 
solving your problem (with the current way gcloud preview app run/deploy works):

a) Having (maybe private) git dependencies in pubspec.yaml *and* let "pub get" 
fetch these dependencies inside the docker container:

(Possible) Advantages:
* Simple directory layout and everything is specified in pubspec.yaml
* No additional steps outside.
* Smaller docker context

Disadvantages
* Requires installing ssh client inside docker container (via `RUN apt-get ...`)
* Requires adding private key to docker container (via `ADD ...`)
* Requires potentially re-cloning on every build (=> very slow)

[To make it slightly faster, one could e.g. clone the git repositories via 
separate `RUN git clone` steps and use path dependencies in pubspec.yaml.]

b) Cloning (maybe private) git dependencies *manually* and use path 
dependencies in pubspec.yaml.

Advantages:
* No need for the private key to be added to the container
* No need to install tools inside the docker container (e.g. ssh)
* Source can come from anywhere (git or some other place)

Disadvantages:
* More steps to outside
* Larger docker context & more complicated way of building the docker image

[If one does not want to having cloned git repositories several times, one can 
- at least on linux - use "mount --bind ~/repositories/<name> 
apengine_app/pkg/<name>]

Option b) is IMHO the better approach. To make restarting time low one needs to 
do two tings

1) Add all files/directories which are not needed for the app to run into 
`.dockerignore`: e.g. `.git`, `.pub` directories

2) Make a Dockerfile which allows efficient caching.

Here's an example of a application using several packages:

The layout of the application is:

root/
  - app.yaml
  - .dockerignore
  - app/
      - pubspec.yaml
      - bin/
          - server.dart
  - pkg/
      - <private-dep1>/
          - pubspec.yaml
          - lib/
      - <private-dep2>/
          - pubspec.yaml
          - lib/

The .dockerignore contains e.g.:
  app/.pub
  .git

The Dockerfile could look like:

  FROM google/dart-runtime-base

  WORKDIR /project/app

  ADD app.yaml /project/
  ADD app/pubspec.* /project/app/
  ADD pkg/<private-dep1>/pubspec.* /project/pkg/<private-dep1>/
  ADD pkg/<private-dep2>/pubspec.* /project/pkg/<private-dep2>/

  RUN pub get

  ADD pkg /project/pkg
  ADD app /project/app

  RUN pub get --offline

  ENV DART_VM_OPTIONS --enable-async

To make deploying files faster, one should add a section to `app.yaml` which 
excludes files not used by AppEngine itself (e.g. dart files):

app.yaml:
....

skip_files:
- ^.*/packages.*$
- ^.*\.dart$
- ^\.git/.*$

Original comment by kustermann@google.com on 12 Jan 2015 at 12:27

[GoogleCodeExporter]

I have seen this in the Docker.template 
(https://github.com/dart-lang/dart_docker/blob/master/runtime/Dockerfile.templat
e) as well, but can't find an explanation of why you need to do:

RUN pub get

*then* add the rest of the files, and run

RUN pub get --offline

Why is this necessary?

Original comment by mate...@gmail.com on 8 Jul 2015 at 3:55

[GoogleCodeExporter]

The reason for having two steps is to decrease docker build times 
*significantly* when changing code and rebuilding docker images.

The first "RUN pub get" step will take a long time, since it's hitting the 
internet and downloading potentially many packages from pub.dartlang.org (and 
maybe from other sources). It is therefore advisable to cache this step, so we 
don't have to do it very often. In fact the only reason to re-run this step is 
if the pubspec.{yaml,lock} files have changed, or one wants to use a new base 
docker image (e.g. newer version of Dart).

The docker layer caching will ensure it caches "pub get" and only re-runs it, 
if the base docker image or the pubspec.{yaml,lock} files have changed.

The next step is adding all the remaining dart files and running "RUN pub get 
--offline". So once any of the dart files have changed, they get re-added and 
"pub get --offline" gets re-run. Since it's running in offline mode and all 
external dependencies are cached, this is step is basically just creating 
package/ directories and symlinks (or .packages file, once pub has support for 
the new DEP proposed package spec file).

There have been user reports that the "pub get --offline" step is sometimes 
trying to download something from the internet and fails therefore. This issue 
is tracked via https://github.com/dart-lang/pub/issues/1293

Original comment by kusterma...@gmail.com on 8 Jul 2015 at 5:10