Enabling Cross-Origin Resource Sharing (CORS) for S3 Bucket

Question

Pulumi · Accepted Answer

To enable Cross-Origin Resource Sharing (CORS) for an S3 bucket using Pulumi, you will need to create an S3 bucket and configure its CORS settings accordingly. The CORS configuration includes specifying which origins are allowed to access the bucket, which HTTP methods are allowed from those origins, and other related headers and settings.

Here is a step-by-step guide and a Pulumi TypeScript program to accomplish this:

1. **Define the S3 Bucket**: Using the `aws.s3.Bucket` resource, an S3 bucket will be created where you can host your content.

2. **Configure CORS**: Using the `aws.s3.BucketCorsConfigurationV2` resource, you can specify the CORS rules for your S3 bucket. This configuration includes settings such as `allowedMethods`, `allowedOrigins`, and `allowedHeaders` for the bucket.

3. **Export the Bucket Name**: At the end of the Pulumi program, we export the name of the S3 bucket so that you can easily reference it.

Below is the TypeScript program for creating an S3 bucket with CORS enabled:

```typescript
import * as aws from "@pulumi/aws";

// Create an S3 bucket.
const bucket = new aws.s3.Bucket("my-bucket", {
    // Additional configurations can be added here if needed.
});

// Configure CORS for the bucket.
const bucketCorsConfiguration = new aws.s3.BucketCorsConfigurationV2("my-bucket-cors", {
    bucket: bucket.bucket, // Reference the created S3 bucket.
    corsRules: [{
        allowedHeaders: ["*"],
        allowedMethods: ["GET", "POST"], // Specify the HTTP methods allowed.
        allowedOrigins: ["https://example.com"], // Replace with origins allowed to access the bucket.
        exposeHeaders: ["ETag"],
        maxAgeSeconds: 3000 // Specifies the time in seconds that browser can cache the response for a preflight request.
    }],
});

// Export the name of the bucket.
export const bucketName = bucket.bucket;

```

In the CORS configuration:
- `allowedHeaders` are the headers that are allowed on a request to the S3 bucket from the specified origin.
- `allowedMethods` includes the methods (like `GET`, `POST`, etc.) that you want to allow.
- `allowedOrigins` defines the origins that may access the bucket.
- `exposeHeaders` are the headers that are exposed to the client browser.
- `maxAgeSeconds` is the cache duration for the preflight response, indicating how long the results can be cached for.

Make sure to replace `"https://example.com"` with the actual list of origins that you want to allow. Multiple origins can be allowed by adding them to the `allowedOrigins` array.

Save the Pulumi program in a file `index.ts`, and then use the Pulumi CLI to create and deploy the resources.

Keep in mind that changes in CORS policies may take some time to propagate and be fully in effect. Cross-origin requests that worked previously may fail if you change these settings to be more restrictive.