> For the complete documentation index, see [llms.txt](https://mercure-technologies.gitbook.io/xprem/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mercure-technologies.gitbook.io/xprem/storage/google-cloud-storage.md).

# Google Cloud Storage

Use Google Cloud Storage (GCS) to store and deliver update assets.

### Configure storage

Set these environment variables:

```dotenv
STORAGE_MODE=gcs
GCS_BUCKET_NAME=your-bucket-name
GOOGLE_APPLICATION_CREDENTIALS_B64=<base64-encoded service account JSON>
```

### Create service account credentials

{% stepper %}
{% step %}

#### Create a service account

In the GCP Console, go to **IAM & Admin** → **Service Accounts**.

Create a service account or select an existing one.
{% endstep %}

{% step %}

#### Grant bucket access

Go to **Cloud Storage** → **Buckets** and select your bucket.

Open **Permissions**, then select **Grant Access**. Add the service account with the **Storage Admin** role.
{% endstep %}

{% step %}

#### Create and encode a key

Go to **Service Accounts** → **Keys** → **Add Key** → **Create new key**.

Choose **JSON**, then encode the downloaded file:

```shellscript
base64 -i /path/to/service-account.json | tr -d '\n'
```

Set the result as `GOOGLE_APPLICATION_CREDENTIALS_B64`.
{% endstep %}
{% endstepper %}

{% hint style="info" %}
The credential authenticates object operations and generates signed URLs.
{% endhint %}

### Asset delivery

When a client requests an update, xprem returns a URL for each asset.\
How that URL is produced depends on your configuration.

[**Generic CDN**](/xprem/cdn/generic-cdn.md)**:** set `CDN_BASE_URL` to serve assets through a CDN of your choice. xprem rewrites asset URLs to your CDN hostname, which caches them and reads from your bucket on a miss.

**Direct from storage:** the default once `GOOGLE_APPLICATION_CREDENTIALS_B64` is set. xprem returns pre-signed GCS URLs valid for 15 minutes, so clients download straight from your bucket while it stays private. No CDN configuration is required.

**Through the server:** xprem fetches each object from GCS and streams it back itself. This happens when no `GOOGLE_APPLICATION_CREDENTIALS_B64` is configured, or when the client sends the `prevent-cdn-redirection: true` header. Every asset byte then transits through your server, so size it accordingly.

### Required permissions

Grant the service account the **Storage Admin** role on the bucket. It provides:

* `storage.objects.get` — Read objects.
* `storage.objects.list` — List branches, runtime versions, and updates.
* `storage.objects.create` — Upload updates.
* `storage.objects.delete` — Remove updates.
* Signed URL generation — Deliver assets directly from GCS.


---

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