The Go runtime is the software stack responsible for installing your web service's code and its dependencies and running your service. The Go runtime for App Engine in the standard environment is declared in the [`app.yaml`](https://docs.cloud.google.com/appengine/docs/standard/go/configuring-your-app-with-app-yaml) file: ```yaml runtime: goVERSION ``` Where VERSION is the Go `MAJOR` and `MINOR` version numbers. For example, to use the latest Go version, Go 1.27, specify `127`. For other supported Go versions, and the corresponding Ubuntu version for your Go version, see the [Runtime support schedule](https://docs.cloud.google.com/appengine/docs/standard/lifecycle/support-schedule#go). ## Go version The latest supported Go version is 1.27. The Go runtime uses the latest stable release of the version that is specified in your `app.yaml` file. App Engine automatically updates to new patch revisions, but won't automatically update the major version. For example, your application might be deployed at the minor version Go 1.13.1 and be automatically updated to version 1.13.2 at a later deployment, but it won't be automatically updated to the major version Go 1.14. ## Dependencies For more information on declaring and managing dependencies, see [Specifying dependencies](https://docs.cloud.google.com/appengine/docs/standard/go/specifying-dependencies).
## 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](https://docs.cloud.google.com/appengine/docs/standard/reference/app-yaml#environment_variables), 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.
## Filesystem The runtime includes a writable `/tmp` directory, with all other directories having read-only access. Writing to `/tmp` takes up system memory. For more information, see the [`TempDir`](https://golang.org/pkg/io/ioutil/#TempDir) and [`TempFile`](https://golang.org/pkg/io/ioutil/#TempFile) documentation.
## Metadata server Each instance of your application can use the App Engine metadata server to query information about the instance and your project. > [!NOTE] > **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`.