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Published: Sep 2, 2020 License: Apache-2.0


Template for GAE Standard app

This directory contains "Hello, world" GAE Standard application with all bells and whistles of luci-go framework:

  • HTTP router and middlewares.
  • luci/gae wrapper around datastore for better testability.
  • OpenID based authenticator layer.
  • Application settings store.

Code structure

All luci-go code (including all GAE apps) is built without appengine tag, since we support GAE Standard runtime as well as GAE Flexible runtime (and unit testing environment running locally).

As a consequence, GAE apps must live in valid Go packages, in particular they must not use relative import paths (as advertised by examples for Standard SDK).

Since we still want to run on Standard GAE, we must obey some rules. In particular, Standard GAE Golang SDK enforces that all subpackages imported from GAE module package (e.g. package that contains app.yaml) are using relative import paths. For example, if app.yaml is located in the package go.chromium.org/luci/luci-go/appengine/cmd/helloworld then an attempt to import go.chromium.org/luci/luci-go/appengine/cmd/helloworld/subpackage from .../helloworld/source.go will fail with GAE SDK complaining that imports should be relative (i.e. import "subpackage"). It is a precaution against importing instances of same package via two different import paths (absolute and relative), since in this case all types, init() calls etc are duplicated. More info is here.

Luckily, Standard GAE SDK handles imports from packages not under module root in a same way as normal Golang SDK does. To workaround the weird limitation mentioned above, we put app.yaml (and HTTP routing code) in a separate frontend package, that doesn't have any subpackages.

To summarize, the structure of GAE app is:

  • .../cmd/app/frontend contains app.yaml and code to setup HTTP routes for default GAE module. It can also contain cron.yaml, queues.yaml and other GAE yamls. It must not have subpackages.
  • .../cmd/app/backend contains module-backend.yaml that defines backend GAE module and code to setup HTTP routes for backend module. It must not have subpackages.
  • .../cmd/app/logic1, .../cmd/app/logic2, ... contains actual implementation of app's logic. It is normal Go packages that can have subpackages, tests, etc.

Running on devserver

The simplest way to run the app locally is to use gae.py wrapper around appcfg from luci-py repository.

Clone luci-py somewhere and symlink gae.py as gae.py in GAE application directory (i.e. a directory that contains frontend directory as a child).

If you are using infra.git gclient solution, run:

cd go.chromium.org/luci/luci-go/appengine/cmd/helloworld
ln -s ../../../../../../../../luci/appengine/components/tools/gae.py gae.py
./gae.py devserver

Using the RPC Explorer.

rpcexplorer must be built first.

To build, if you are using infra.git gclient solution and already have node and npm, run:

cd go.chromium.org/luci/web
./web.py build rpcexplorer

For full instructions, see here.

Once rpcexplorer is built and the devserver is running (e.g. at localhost:8080), visit localhost:8080/rpcexplorer/.

Deploying and configuring

Use gae.py to deploy:

./gae.py upload -A <appid>
./gae.py switch -A <appid>

When deployed for a first time you'd need to configure OAuth2 client (used for OpenID login flow) and URL of an auth service to grab user groups from.

To configure OAuth2:

  1. Go to Cloud Console for some project of your choosing (not necessarily same one that GAE app belongs to).
  2. On "Credentials" tab of "API Manager" service create a new web application OAuth 2.0 client ID (using "Add Credentials" button and choosing "Web application" type).
  3. In "Authorized redirect URIs" add https://<yourapp>.appspot.com/auth/openid/callback.
  4. As a result you'll get client ID and client secret strings. Note them.
  5. Go to https://<yourapp>.appspot.com/admin/portal/openid_auth. You must be GAE level administrator of the app to access this page.
  6. In "Discovery URL" field enter https://accounts.google.com/.well-known/openid-configuration
  7. In "OAuth client ID", "OAuth client secret" and "Redirect URI" fields put values you used when configuring client ID in the Cloud Console.
  8. Click "Save settings". One minute later OpenID authentication should start working.

It is possible to reuse existing OAuth 2.0 web clients. Just add a new redirect URI to the list of authorized redirect URIs.

To start using auth groups from some existing auth service (e.g. chrome-infra-auth.appspot.com):

  1. Go to Cloud Console project that contain your GAE app.
  2. In "API Manager" section enable "Google Cloud Pub/Sub" API.
  3. Go to https://<yourapp>.appspot.com/admin/portal/auth_service.
  4. Note service account ID corresponding to your GAE app. It is highlighted in bold in "Authorization settings" section.
  5. Add this account to auth-trusted-services group on the auth service. You must be an admin on auth server to be able to do so.
  6. Put URL of the auth server into "Auth service URL" field, click "Save settings".


Path Synopsis
Package main implements HTTP server that handles requests to default module.
Package main implements HTTP server that handles requests to default module.

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