# Create a Go app in the App Engine flexible environment
### Region ID
The `REGION_ID` is an abbreviated code that Google assigns
based on the region you select when you create your app. The code does not
correspond to a country or province, even though some region IDs may appear
similar to commonly used country and province codes. For apps created after
February 2020, `REGION_ID.r` is included in
App Engine URLs. For existing apps created before this date, the
region ID is optional in the URL.
Learn more
[about region IDs](https://docs.cloud.google.com/appengine/docs/flexible/go/how-requests-are-routed#region-id).
> [!NOTE]
> **Note:** If you are deploying a new Go web service to Google Cloud, we recommend getting started with [Cloud Run](https://docs.cloud.google.com/run/docs/quickstarts/build-and-deploy/deploy-go-service).
This quickstart demonstrates how to create and deploy an app that displays a
short message. You can use the sample application in this quickstart for any [supported](https://docs.cloud.google.com/appengine/docs/flexible/lifecycle/support-schedule#go) version of Go, by specifying the runtime
version and operating system in your [`app.yaml`](https://docs.cloud.google.com/appengine/docs/flexible/go/runtime#newversions)
file.
## Before you begin
### Required roles
To get the permissions that
you need to complete this quickstart,
ask your administrator to grant you the
following IAM roles:
- [App Engine Admin](https://docs.cloud.google.com/iam/docs/roles-permissions/appengine#appengine.appAdmin) (`roles/appengine.appAdmin`) on the project
- [Cloud Build Editor](https://docs.cloud.google.com/iam/docs/roles-permissions/cloudbuild#cloudbuild.builds.editor) (`roles/cloudbuild.builds.editor`) on the project
- [Storage Object Admin](https://docs.cloud.google.com/iam/docs/roles-permissions/storage#storage.objectAdmin) (`roles/storage.objectAdmin`) on the project
- [Logs Viewer](https://docs.cloud.google.com/iam/docs/roles-permissions/logging#logging.viewer) (`roles/logging.viewer`) on the project
- [Service Account User](https://docs.cloud.google.com/iam/docs/roles-permissions/iam#iam.serviceAccountUser) (`roles/iam.serviceAccountUser`) on the service account
- Ask your administrator to grant the following roles for the App Engine default service account:
- [Artifact Registry Reader](https://docs.cloud.google.com/iam/docs/roles-permissions/artifactregistry#artifactregistry.reader) (`roles/artifactregistry.reader`) on the project
- [Cloud Build Service Account](https://docs.cloud.google.com/iam/docs/roles-permissions/cloudbuild#cloudbuild.builds.builder) (`roles/cloudbuild.builds.builder`) on the project
- [Storage Object Viewer](https://docs.cloud.google.com/iam/docs/roles-permissions/storage#storage.objectViewer) (`roles/storage.objectViewer`) on the project
For more information about granting roles, see [Manage access to projects, folders, and organizations](https://docs.cloud.google.com/iam/docs/granting-changing-revoking-access).
You might also be able to get
the required permissions through [custom
roles](https://docs.cloud.google.com/iam/docs/creating-custom-roles) or other [predefined
roles](https://docs.cloud.google.com/iam/docs/roles-overview#predefined).
## Additional prerequisites
1. Initialize your App Engine app with your project and choose its region:
gcloud app create --project=[YOUR_PROJECT_ID]
When prompted, select the [region](https://docs.cloud.google.com/appengine/docs/flexible/locations)
where you want to locate your App Engine application.
> [!CAUTION]
> **Caution**: You cannot change an app's region once it has been set.
2. Install the following on your local machine:
- [Download
and install Git](https://git-scm.com/).
- Run the following command to install the
[gcloud component](https://docs.cloud.google.com/sdk/docs/managing-components) that includes the
App Engine extension for Go:
gcloud components install app-engine-go
### App Engine locations
App Engine is *regional* , which means the infrastructure that runs your apps is
located in a specific region, and Google manages it so that it is available
redundantly across
[all of the zones within that region](https://docs.cloud.google.com/docs/geography-and-regions).
Meeting your latency, availability, or durability requirements are primary
factors for selecting the region where your apps are run. You can generally
select the region nearest to your app's users, but you should consider [the
locations where App Engine is available](https://cloud.google.com/about/locations/#region)
as well as the [locations](https://cloud.google.com/about/locations/#region) of the other
Google Cloud products and services that your app uses. Using services
across multiple locations can affect your app's latency as well as its
[pricing](https://cloud.google.com/appengine/pricing).
You cannot change an app's region after you set it.
> [!NOTE]
> **Note:** Two locations, which are called `europe-west` and `us-central` in App Engine commands and in the Google Cloud console, are called `europe-west1` and `us-central1`, respectively, elsewhere in Google documentation.
If you already created an App Engine application, you can view its
region by doing one of the following:
- Run the `gcloud app describe` command.
- Open the
[App Engine Dashboard in the Google Cloud console](https://console.cloud.google.com/appengine).
The region appears near the top of the page.
This quickstart assumes that you are familiar with the Go programming language
and that you have [installed Go](https://golang.org/doc/install).
## Download the Hello World app
We've created a Hello World app for App Engine so you can quickly
get a feel for deploying an app to the Google Cloud.
1. Clone the Hello World sample app repository to your local machine.
git clone https://github.com/GoogleCloudPlatform/golang-samples
2. Change to the directory that contains the sample code.
cd golang-samples/appengine_flexible/helloworld
## Run Hello World on your local machine
To run the Hello World app on your local computer:
1. Start a local web server.
go run *.go
2. In your web browser, enter the following address:
If you are using Cloud Shell, in the toolbar, click
**Web Preview**  and
select **Preview on port 8080** instead.
The **Hello World** message from the sample app displays on the page. In your
terminal window, press **Ctrl+C** to exit the web server.
## Deploy and run Hello World on App Engine
To deploy your app to the App Engine flexible environment:
1.
Deploy the Hello World app by running the following
command from the `helloworld` directory:
```bash
gcloud app deploy
```
Learn about the
[optional flags](https://docs.cloud.google.com/appengine/docs/flexible/go/create-app#deploy_and_run_hello_world_on_app_engine).
### Common `gcloud` command flags
- Include the `--version` flag to specify an ID that uniquely identifies that version of your app, otherwise one is generated for you. Example: `--version [YOUR_VERSION_ID]`
- Include the `--project` flag to specify an alternate Google Cloud project ID to what you initialized as the default in the `gcloud` tool. Example: `--project [YOUR_PROJECT_ID]`
Example:
```
gcloud app deploy --version pre-prod-5 --project my-sample-app
```
To learn more about deploying your app from the command line, see
[Testing and Deploying Your App](https://docs.cloud.google.com/appengine/docs/flexible/testing-and-deploying-your-app)
. For a list of all the command flags, see the
`https://docs.cloud.google.com/sdk/gcloud/reference/app/deploy`
reference.
2.
Launch your browser to view the app at
`https://PROJECT_ID.https://docs.cloud.google.com/appengine/docs/flexible/go/create-app#appengine-urls.r.appspot.com`
```bash
gcloud app browse
```
where `PROJECT_ID` represents your Google Cloud project ID.
This time, the page that displays the Hello World message is delivered by a
web server running on an App Engine instance.
**Congratulations!** You've deployed your first App Engine app to the
App Engine flexible environment!
If you encountered any errors deploying your application, check the [troubleshooting tips](https://docs.cloud.google.com/appengine/docs/flexible/testing-and-deploying-your-app#troubleshooting).
See the following sections for information about cleaning up as well as links to
possible next steps that you can take.
## Clean up
To avoid incurring charges, you can delete your Google Cloud project to stop
billing for all the resources used within that project.
> [!CAUTION]
> **Caution** : Deleting a project has the following effects:
>
> - **Everything in the project is deleted.** If you used an existing project for the tasks in this document, when you delete it, you also delete any other work you've done in the project.
> - **Custom project IDs are lost.** When you created this project, you might have created a custom project ID that you want to use in the future. To preserve the URLs that use the project ID, such as an `appspot.com` URL, delete selected resources inside the project instead of deleting the whole project.
1. In the Google Cloud console, go to the **Manage resources** page.
[Go to Manage resources](https://console.cloud.google.com/iam-admin/projects)
2. In the project list, select the project that you want to delete, and then click **Delete**.
3. In the dialog, type the project ID, and then click **Shut down** to delete the project.
## What's next
#### Learn the whole platform
Now that you know what it's like to develop and deploy App Engine apps,
you can explore the rest of Google Cloud. You already have the
Google Cloud CLI installed which gives you the tools to interact with
products like Cloud SQL, Cloud Storage, Firestore,
and more.
#### Learn about the App Engine flexible environment
Here are some topics to help continue your learning about App Engine:
- [An overview of App Engine](https://docs.cloud.google.com/appengine/docs/flexible/an-overview-of-app-engine)
- [Request routing](https://docs.cloud.google.com/appengine/docs/flexible/how-requests-are-routed)
- [Request handling](https://docs.cloud.google.com/appengine/docs/flexible/how-requests-are-handled)
- [Managing instances](https://docs.cloud.google.com/appengine/docs/flexible/how-instances-are-managed)
## Hello World code review
Hello World is the simplest possible App Engine app, as it contains only
one service, has only one version, and all of the code is located within the
app's root directory. This section describes each of the app files in detail.
#### `helloworld.go`
The `helloworld.go` file registers a handler that listens for requests to `/`,
and responds with the 'Hello world!' message.
package main
import (
"fmt"
"log"
"net/http"
"os"
)
func main() {
http.HandleFunc("/", handle)
port := os.Getenv("PORT")
if port == "" {
port = "8080"
}
log.Printf("Listening on port %s", port)
if err := http.ListenAndServe(":"+port, nil); err != nil {
log.Fatal(err)
}
}
func handle(w http.ResponseWriter, r *http.Request) {
if r.URL.Path != "/" {
http.NotFound(w, r)
return
}
fmt.Fprint(w, "Hello world!")
}
#### `app.yaml`
The [`app.yaml`](https://docs.cloud.google.com/appengine/docs/flexible/go/configuring-your-app-with-app-yaml)
file describes the following configuration for your app:
- Sets `env: flex`, indicating your app uses the [App Engine flexible environment](https://docs.cloud.google.com/appengine/docs/flexible).
- Specifies the runtime used by the app.
# Copyright 2019 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
runtime: go
env: flex
runtime_config:
operating_system: 'ubuntu22'
runtime_version: 1.25
# This sample incurs costs to run on the App Engine flexible environment.
# The settings below are to reduce costs during testing and are not appropriate
# for production use. For more information, see:
# https://docs.cloud.google.com/appengine/docs/flexible/go/configuring-your-app-with-app-yaml
manual_scaling:
instances: 1
resources:
cpu: 1
memory_gb: 0.5
disk_size_gb: 10
- For more information on how the Go runtime works, see
[The Go runtime](https://docs.cloud.google.com/appengine/docs/flexible/go/runtime).
- For more details about how to design your app to take advantage of versions
and services, see
[An overview of App Engine](https://docs.cloud.google.com/appengine/docs/flexible/an-overview-of-app-engine).
- For more details about the configuration settings for App Engine, see
[Configuring your app with app.yaml](https://docs.cloud.google.com/appengine/docs/flexible/go/configuring-your-app-with-app-yaml).