# App Engine

[App Engine](https://cloud.google.com/appengine/docs/standard/java11) is a fully managed Platform-as-a-Service that can run your application, provision a HTTPS load balancer, and scale out your workload as needed. When no one is using your application, it can scale down to zero.

{% embed url="<https://www.youtube.com/watch?v=qx_T6-EKkBE>" %}

## Getting Started

### Clone

```bash
cd $HOME
git clone https://github.com/saturnism/jvm-helloworld-by-example
cd jvm-helloworld-by-example/helloworld-springboot-tomcat
```

### Build

```bash
./mvnw package
```

### Deploy

```bash
gcloud app deploy target/helloworld.jar
```

{% hint style="info" %}
If this is your first time using App Engine on the project, you'll be prompted to choose a region. Pick the region that's most suitable for your application. This site mostly uses `us-central` as an example.
{% endhint %}

{% hint style="warning" %}
Once you select the region, you cannot change it for an App Engine application.
{% endhint %}

### Connect

Once deployed, the command will output the HTTPs URL. To open the URL in your browser:

```bash
gcloud app browse
```

To find the URL without opening the browser:

```bash
gcloud app browse --no-launch-browser
```

You can `curl` the URL:

```bash
URL=$(gcloud app browse --no-launch-browser)
curl ${URL}
```

{% hint style="info" %}
You can run any Java service in App Engine as long as it's packaged as a JAR file, and can be executed with `java -jar app.jar`.
{% endhint %}

## Additional Configuration

By default, App Engine will deploy with the smallest `F1`instance class. You can specify a larger instance, configure environment variables, and more tuning parameters using an `app.yaml`:

{% code title="app.yaml" %}

```
runtime: java11
instance_class: F4
env_variables:
  SPRING_PROFILES_ACTIVE: "prod"
```

{% endcode %}

{% hint style="info" %}
See [App Engine Standard Instance Classes documentation](https://cloud.google.com/appengine/docs/standard#instance_classes) for a list of Instance Classes and associated CPU/Memory resources.
{% endhint %}

Deploy the JAR file with the configuration:

```bash
gcloud app deploy target/helloworld.jar \
  --appyaml app.yaml
```

{% hint style="info" %}
Learn more about the configurations in [app.yaml reference documentation](https://cloud.google.com/appengine/docs/standard/java11/config/appref).
{% endhint %}

## Learn More

* [App Engine Java 11 documentation](https://cloud.google.com/appengine/docs/standard/java11)
* [Deploy with App Engine Maven plugin](https://cloud.google.com/appengine/docs/standard/java11/using-maven#setting_up_maven)
* [Deploy with App Engine Gradle plugin](https://cloud.google.com/appengine/docs/standard/java11/using-gradle)


---

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