The Go runtime

The Go runtime is the software stack responsible for installing your application code and dependencies, and then running that application in the flexible environment.

Go versions

Go 1.23 (preview) uses buildpacks. For the full list of supported Go versions, and their corresponding Ubuntu version, see the Runtime support schedule.

To use a supported Go version, you must:

Install gcloud CLI version 420.0.0 or later. You can update your CLI tooling by running the gcloud components update command. To view your installed version, you can run the gcloud version command.
Go recommends that you use a go.mod file for managing dependencies. To install dependencies during deployment, include a go.mod file in the same folder as the app.yaml file.

For example, the folder structure of your app with go.mod must represent:
```
<application-root>/
--> app.yaml
--> go.mod
--> Other source files used in your application.
```
Include the runtime_config and operating_system settings in your app.yaml file to specify an operating system.
Optionally, you can specify a runtime version by including the runtime_version setting in your app.yaml. By default, the latest Go version is used if the runtime_version setting is not specified.

Examples

To specify Go 1.23 (preview) on Ubuntu 22:

runtime: go
env: flex

runtime_config:
    operating_system: "ubuntu22"
    runtime_version: "1.23"

To specify the latest supported Go version on Ubuntu 22:

  runtime: go
  env: flex

  runtime_config:
      operating_system: "ubuntu22"

Your app 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 it won't automatically update the major version.

For example, your application might be deployed at Go 1.18.10, and later it might be automatically updated to Go 1.18.11, but it won't be automatically updated to the major version Go 1.19.

Choosing Go 1.23 (preview) in your app.yaml file results in the latest patch version of Go 1.23 (preview) available.

  runtime: go
  env: flex

  runtime_config:
      operating_system: "ubuntu22"
      runtime_version: "1.23"

See the app.yaml reference for more information.

Previous runtime versions

To use Go version 1.15 and earlier, specify a version in runtime setting using the go1.x format in your app.yaml file. For example:

  runtime: go1.14
  env: flex

If no version is specified, the default version of go1.11 will be automatically selected.

For example, your application might be deployed at Go 1.14.10, and later it might be automatically updated to Go 1.14.11, but it won't be automatically updated to the major version Go 1.15.

Choosing the go runtime version go1.15 in your app.yaml file results in the latest version of 1.15 available, for example, 1.15.15.

  runtime: go1.15
  env: flex

Support for other Go runtimes

If you need to use a Go version that isn't supported, you can create a custom runtime and select a valid base image with the Go version you need.

For Google-supplied base images or Docker Go base images, see Building custom runtimes.

Import packages

Your code compiles when you deploy your app to App Engine. When you run the deployment command, your app's dependencies are first collected from your local GOPATH and then they are all sent to the build server. Any missing dependencies, for example third-party libraries, results in build failures.

To avoid build failures and ensure that all your app's dependencies get deployed with your code, you should test your app locally before deploying it.

Extending the runtime

For instructions on how to extend and customize the Go runtime, read the Go runtime builder on GitHub.

Metadata server

Each instance of your application can use the Compute Engine metadata server to query information about the instance, including its host name, external IP address, instance ID, custom metadata, and service account information. App Engine does not allow you to set custom metadata for each instance, but you can set project-wide custom metadata and read it from your App Engine and Compute Engine instances.

Use the cloud.google.com/go/compute/metadata package to access the metadata server.