This package provides support for running server applications written in Dart on Google App Engine using Custom Runtimes with Flex Environment.

This page assumes the Dart SDK (see dartlang.org/install) as well as the Google Cloud SDK (see cloud.google.com/sdk) were installed and their bin folders have been added to PATH.

To ensure gcloud was authorized to access the cloud project and we have the app component installed, we assume the following has been run:

$ gcloud auth login
$ gcloud config set project <project-name>
$ gcloud components update app

Furthermore in order to operate on the data of the cloud project, a service account needs to be created which allows downloading a private key in JSON format. Such a key can be obtained via the Cloud Console under IAM & Admin > Service Accounts > Create Service Account.

To setup a hello world application we need 4 different things:

name: hello_world
version: 0.1.0
environment:
  sdk: '>=2.0.0 <3.0.0'

dependencies:
  appengine: ^0.6.0

runtime: custom
env: flex
service: default

FROM google/dart-runtime

### NOTE: Uncomment the following lines for local testing:
#ADD key.json /project/key.json
#ENV GCLOUD_KEY /project/key.json
#ENV GCLOUD_PROJECT dartlang-pub

import 'dart:io';
import 'package:appengine/appengine.dart';

requestHandler(HttpRequest request) {
  request.response
      ..write('Hello, world!')
      ..close();
}

main() async {
  await runAppEngine(requestHandler);
}

There are two ways to run the application locally - with or without docker. Both of which require a service account key.

The simplest way to run the application is on the command line like this:

$ export GCLOUD_KEY=<path-to-service-account-key.json>
$ export GCLOUD_PROJECT=<project-name>
$ dart bin/server.dart

This will serve the application at localhost:8080!

To be closer to the production environment one can run the application inside a docker container. In order to do so, docker needs to be installed first (see the official instructions.

In order to run the application locally we uncomment the 3 lines in the Dockerfile and place the service account key in under app/key.json:

ADD key.json /project/key.json
ENV GCLOUD_KEY /project/key.json
ENV GCLOUD_PROJECT dartlang-pub

We can then run the application via:

$ docker build .
...
Sucessfully built <docker-imgage-hash>
$ docker run -it <docker-imgage-hash>
...

In order to find out at which IP the Docker container is available we inspect the running container via:

$ docker ps
CONTAINER ID        IMAGE               COMMAND             CREATED             STATUS              PORTS               NAMES
<container-id>       ...
app % docker inspect --format '{{ .NetworkSettings.IPAddress }}' <container-id>
172.17.0.2

Then the application will be available at 172.17.0.2:8080.

Before deploying the app, be sure to remove the environment variables in the Dockerfile which we used for local testing!

To deploy the application to the cloud we run the following command (optionally passing the --no-promote flag to avoid replacing the production version)

$ gcloud app deploy --no-promote app.yaml
...
Updating service [default]...done.
Deployed service [default] to [https://<version-id>-dot-<project-id>.appspot.com]
...

This will perform a remote docker build in the cloud and deploy a new version. You can find the URL to the version that got deployed in the output of gcloud app deploy (as well as via the Cloud Console under AppEngine > Versions).

The gcloud sdk provides an easy-to-use datastore emulator. The emulator can be launched via

$ gcloud beta emulators datastore start
...
[datastore] If you are using a library that supports the DATASTORE_EMULATOR_HOST
[datastore] environment variable, run:
[datastore] 
[datastore]   export DATASTORE_EMULATOR_HOST=localhost:8268
[datastore] 
[datastore] Dev App Server is now running.
...

To make the application use the emulator, the DATASTORE_EMULATOR_HOST environment variable needs to be set (in addition to the other variables):

$ export DATASTORE_EMULATOR_HOST=localhost:8268
$ export GCLOUD_KEY=<path-to-service-account-key.json>
$ export GCLOUD_PROJECT=<project-name>
$ dart bin/server.dart