Node.js Runtime Environment

The Node.js runtime is the software stack responsible for installing your web service's code and its dependencies and running your service.

The Node.js runtime for App Engine in the standard environment is declared in the app.yaml file:

runtime: nodejsVERSION

Where VERSION is the Node.js MAJOR version number. For example, to use the latest Node.js version, Node.js 20, specify 20.

For other supported Node.js versions, and the corresponding Ubuntu version for your Node.js version, see the Runtime support schedule.

Node.js version

The Node.js runtime uses the latest stable release of the version that is specified in your app.yaml file. App Engine automatically updates to new patch and minor release versions, but it will not automatically update the major version.

For example, your application might be deployed at Node.js 10.9.4 and later automatically updated to version 10.10.0, but it will not be automatically updated to Node.js 12.x.x.

Because minor and patch versions are automatically updated, if present, the engines.node property in your package.json file can only specify the major version and be compatible with the Node.js version specified in your app.yaml file.

For example for 20:

• 20.x.x
• ^20.0.0
• ~20
• >=6

If you specify an incompatible Node.js version in your package.json file, your deployment will fail with an error message.

Dependencies

During deployment, the runtime installs your dependencies using the npm install command. The runtime also supports Yarn (yarn.lock) and Pnpm (pnpm-lock.yaml) package managers. For more information, see Specifying Dependencies. Because the runtime performs a fresh install, you do not need to upload your node_modules folder.

Note: By default, the gcloud CLI does not upload your node_modules folder. You can change which files are ignored using the .gcloudignore file.

To support Node.js packages that require native extensions, the runtime includes system packages enabling you to use tools such as ImageMagick, FFmpeg, and Chrome headless. See the full list of packages at Included System Packages. To request a package, file an issue in the issue tracker.

NPM build script

By default, the Node.js runtime executes npm run build if a build script is detected in package.json. If you require additional control over your build steps before starting your application, you can provide a custom build step by adding a gcp-build script to your package.json file.

To prevent your build from running the npm run build script, you must either:

• Add a gcp-build script with an empty value in your package.json file: "gcp-build":"". For details about configuring the package.json, see Node.js buildpacks configurations.

• Add the GOOGLE_NODE_RUN_SCRIPTS build environment variable with an empty value in your app.yaml file.

  build_env_variables:
    GOOGLE_NODE_RUN_SCRIPTS: ''
  

For details about specifying build environment variables see build_env_variables section in the app.yaml file.

Application startup

By default, the runtime starts your application by running node server.js. If you specify a start script in your package.json file, the runtime runs the specified start script instead. For example:

"scripts": {
  "start": "node app.js"
}

For your app to receive HTTP requests, your start script should start a web server that listens on host 0.0.0.0 and the port specified by the PORT environment variable, which is accessible in Node.js as process.env.PORT.

For the best performance, the start script should be lightweight and exclude build steps, because it runs whenever a new instance of your application is created.

You can override this behavior by specifying a script in the entrypoint field in app.yaml. Instead of running node server.js or a start script, the runtime starts your application with the command you specify in entrypoint.

Environment variables

The following environment variables are set by the runtime:

Environment variable	Description
GAE_APPLICATION	The ID of your App Engine application. This ID is prefixed with 'region code~' such as 'e~' for applications deployed in Europe.
GAE_DEPLOYMENT_ID	The ID of the current deployment.
GAE_ENV	The App Engine environment. Set to standard.
GAE_INSTANCE	The ID of the instance on which your service is currently running.
GAE_MEMORY_MB	The amount of memory available to the application process, in MB.
GAE_RUNTIME	The runtime specified in your app.yaml file.
GAE_SERVICE	The service name specified in your app.yaml file. If no service name is specified, it is set to default.
GAE_VERSION	The current version label of your service.
GOOGLE_CLOUD_PROJECT	The Google Cloud project ID associated with your application.
PORT	The port that receives HTTP requests.
NODE_ENV (Only available in the Node.js runtime)	Set to production when your service is deployed.

You can define additional environment variables in your app.yaml file, but the above values cannot be overridden, except for NODE_ENV.

HTTPS and forwarding proxies

App Engine terminates HTTPS connections at the load balancer and forwards requests to your application. Some applications need to determine the original request IP and protocol. The user's IP address is available in the standard X-Forwarded-For header. Applications that require this information should configure their web framework to trust the proxy.

With Express.js, use the trust proxy setting:

app.set('trust proxy', true);

Note that setting trust proxy to true can open up the req.ip property to IP spoofing vulnerability.

Filesystem

The runtime includes a full filesystem. The filesystem is read-only except for the location /tmp, which is a virtual disk storing data in your App Engine instance's RAM.

Metadata server

Each instance of your application can use the App Engine metadata server to query information about the instance and your project.

Note: Custom metadata is not supported in the standard environment.

You can access the metadata server through the following endpoints:

• http://metadata
• http://metadata.google.internal

Requests sent to the metadata server must include the request header Metadata-Flavor: Google. This header indicates that the request was sent with the intention of retrieving metadata values.

The following table lists the endpoints where you can make HTTP requests for specific metadata:

Metadata endpoint	Description
/computeMetadata/v1/project/numeric-project-id	The project number assigned to your project.
/computeMetadata/v1/project/project-id	The project ID assigned to your project.
/computeMetadata/v1/instance/region	The region the instance is running in.
/computeMetadata/v1/instance/service-accounts/default/aliases
/computeMetadata/v1/instance/service-accounts/default/email	The default service account email assigned to your project.
/computeMetadata/v1/instance/service-accounts/default/	Lists all the default service accounts for your project.
/computeMetadata/v1/instance/service-accounts/default/scopes	Lists all the supported scopes for the default service accounts.
/computeMetadata/v1/instance/service-accounts/default/token	Returns the auth token that can be used to authenticate your application to other Google Cloud APIs.

For example, to retrieve your project ID, send a request to http://metadata.google.internal/computeMetadata/v1/project/project-id.