appengine

Dart support for Google AppEngine

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

Status: Experimental

NOTE: This package is currently experimental and published under the labs.dart.dev pub publisher in order to solicit feedback.

For packages in the labs.dart.dev publisher we generally plan to either graduate the package into a supported publisher (dart.dev, tools.dart.dev) after a period of feedback and iteration, or discontinue the package. These packages have a much higher expected rate of API and breaking changes.

Your feedback is valuable and will help us evolve this package. For general feedback, suggestions, and comments, please file an issue in the bug tracker.

Prerequisites

Install Dart and Cloud SDKs

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

Setup gcloud

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

Instead of running gcloud auth application-default login it is also possible to authenticate by making the environment variable GOOGLE_APPLICATION_CREDENTIALS point to a file containing exported service account credentials.

Creating a hello world application

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

An app/pubspec.yaml file describing the Dart package:

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

dependencies:
  appengine: ^0.12.0

An app/app.yaml file describing the AppEngine app:

runtime: custom
env: flex
service: default

An app/Dockerfile describing how to build/bundle the app:

FROM google/dart-runtime

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

This requires exported service account credentials in key.json.

An app/bin/server.dart containing the app code

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

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

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

Running the app locally

There are two ways to run the application locally - with or without docker.

Running without Docker

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

$ gcloud auth application-default login
$ export GOOGLE_CLOUD_PROJECT=<project-name>
$ dart bin/server.dart

This will serve the application at localhost:8080!

Running with Docker

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 key.json:

ADD key.json /project/key.json
ENV GOOGLE_APPLICATION_CREDENTIALS /project/key.json
ENV GOOGLE_CLOUD_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.

Deployment

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).

Regenerating protobuf

You need to have protoc in $PATH. Run the tool/fetch_protos_and_regenerate_dart.sh script. It will fetch the latest protos and compile them for dart using the protoc_plugin in dev_dependencies.