The Go Runtime

Overview

The Go runtime in the flexible environment is the software stack responsible for building and running your code.

To choose the Go runtime in the flexible environment, add two lines to your app.yaml file.

runtime: go
env: flex

Runtimes in the flexible environment are built using Docker. The source code for the Go runtime is available on GitHub.

Go version

Consult the GO_VERSION variable in the Dockerfile to see the version of Go used to build your application.

If the version is updated, you must re-deploy your application to build it against a new runtime.

Importing packages

Your code is compiled 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

You can extend and customize the runtime by modifying the default Dockerfile. First, generate the Dockerfile:

gcloud beta app gen-config --custom

Finally, change runtime: go in your app.yaml file:

runtime: custom

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.

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App Engine flexible environment for Go