# Go App Engine for Managed VMs

This repository supports the Go runtime for Managed VMs on App Engine.
It provides APIs for interacting with App Engine services.
Its canonical import path is `google.golang.org/appengine`.

See https://cloud.google.com/appengine/docs/go/managed-vms/
for more information.

## Directory structure
The top level directory of this repository is the `appengine` package. It
contains the
basic types (e.g. `appengine.Context`) that are used across APIs. Specific API
packages are in subdirectories (e.g. `datastore`).

There is an `internal` subdirectory that contains service protocol buffers,
plus packages required for connectivity to make API calls. App Engine apps
should not directly import any package under `internal`.

## Updating a Go App Engine app

This section describes how to update a traditional Go App Engine app to run on Managed VMs.

### 1. Update YAML files

The `app.yaml` file (and YAML files for modules) should have these new lines added:
```
vm: true
manual_scaling:
  instances: 1
```
See https://cloud.google.com/appengine/docs/go/modules/#Go_Instance_scaling_and_class for details.

### 2. Update import paths

The import paths for App Engine API packages need to be made relative to `google.golang.org/appengine`.
You can do that manually, or by running this command to recursively update all Go source files in the current directory:
(may require GNU sed)
```
sed -i '/"appengine/{s,"appengine,"google.golang.org/appengine,;s,appengine_,appengine/,}' \
  $(find . -name '*.go')
```

### 3. Update code using deprecated, removed or modified APIs

Most App Engine services are available with exactly the same API.
A few APIs were cleaned up, and some are not available yet.
This list summarises the differences:

* `appengine.Datacenter` now takes an `appengine.Context` argument.
* `datastore.PropertyLoadSaver` has been simplified to use slices in place of channels.
* `search.FieldLoadSaver` now handles document metadata.
* `taskqueue.QueueStats` no longer takes a maxTasks argument. That argument has been
  deprecated and unused for a long time.
* `appengine/aetest`, `appengine/blobstore`, `appengine/cloudsql`
  and `appengine/runtime` have not been ported yet.
* `appengine.BackendHostname` and `appengine.BackendInstance` were for the deprecated backends feature.
  Use `appengine.ModuleHostname`and `appengine.ModuleName` instead.
* `appengine.IsCapabilityDisabled` and `appengine/capability` are obsolete.
* Most of `appengine/file` is deprecated. Use [Google Cloud Storage](https://code.google.com/p/google-api-go-client/wiki/GettingStarted) instead.
* `appengine/socket` is deprecated. Use the standard `net` package instead.
