The Cloud SDK includes a local development server
dev_appserver.py). You can use the local development server to simulate
running your application in production App Engine as well as use it to
access App Engine bundled services.
The simulated environment enforces some sandbox restrictions, such as restricted system functions and Python 3 module imports, but not others, like request time-outs or quotas.
The local development server also simulates the services provided by the libraries in the SDK for App Engine, including Datastore, Memcache, and Task Queues, by performing their tasks locally. When your application is running in the development server, you can still make remote API calls to the production infrastructure using Google APIs HTTP endpoints.
Running the local development server
After you create the
configuration file for your app, you can start the local development server with
dev_appserver.py command to run your app locally.
To start the local development server:
Running the local development server (
To run the local development server, you can either run
specifying the full directory path or you can add
dev_appserver.py to your
PATH environment variable. The tool is located at
Tip: To add the Google Cloud SDK tools to your PATH and enable command-completion in your bash shell, you can run:
dev_appserver.pycommand as follows from the directory that contains your app's
Specify the directory path to your app, for example:
dev_appserver.py --runtime_python_path=/usr/bin/python3 [PATH_TO_YOUR_APP]
You can also set the argument to a comma-separated key-value list like this:
dev_appserver.py --runtime_python_path="python27=/user/bin/python2.7,python3=/usr/bin/python3" [PATH_TO_YOUR_APP]
Alternatively, you can specify the configuration file of a specific service, for example:
dev_appserver.py --runtime_python_path=/usr/bin/python3 app.yaml
To change the port, you include the
dev_appserver.py --runtime_python_path=/usr/bin/python3 --port=9999 [PATH_TO_YOUR_APP]
To learn more about the
dev_appserver.pycommand options, see Local Development Server Options.
The local development server is now running and listening for requests. You
can visit http://localhost:8080/ in your
web browser to see the app in action.
If you specified a custom port with the
--portoption, remember to open your browser to that port.
To stop the local server from the command line, you press the following:
- macOS or Linux: Control-C
- Windows: Control-Break
Specifying application IDs
To access your App ID in the local server, for example to spoof an email address, use the function. To get the hostname of the running app, use the function.
Detecting application runtime environment
Using the Users service
App Engine provides a
Users Service to simplify
authentication and authorization for your application. The local development
server simulates the behavior of Google
with its own sign-in and sign-out pages. While running under the local
development server, the
functions return URLs for
/_ah/logout on the local server.
The local development server can send email for calls to the App Engine mail service using either an SMTP server or a local installation of Sendmail.
To enable mail support with an SMTP server, invoke
dev_appserver.py --smtp_host=smtp.example.com --smtp_port=25 \ --smtp_user=ajohnson --smtp_password=k1tt3ns [PATH_TO_YOUR_APP]
where you set the
--smtp_password options with your own values.
To enable mail support with Sendmail, invoke
dev_appserver.py as follows:
dev_appserver.py --enable_sendmail=yes [PATH_TO_YOUR_APP]
The local server will use the
sendmail command to send email messages with
your installation's default configuration.
Using URL Fetch
When your application uses the URL fetch API to make an HTTP request, the local development server makes the request directly from your computer. The URL Fetch behavior on the local server may differ from production App Engine if you use a proxy server for accessing websites.