Fix "No Access-Control-Allow-Origin header" for S3 and CloudFront

To avoid the error "No 'Access-Control-Allow-Origin' header is present on the requested resource":

  • Enable CORS on your S3 bucket
  • Forward the appropriate headers on your CloudFront distribution

Enable CORS on S3 Bucket

In S3 -> [your bucket] -> Permissions -> Cross-origin resource sharing (CORS):

[
    {
        "AllowedHeaders": [
            "*"
        ],
        "AllowedMethods": [
            "GET"
        ],
        "AllowedOrigins": [
            "*"
        ],
        "ExposeHeaders": []
    }
]

ref:
https://docs.aws.amazon.com/AmazonS3/latest/userguide/cors.html
https://docs.aws.amazon.com/AmazonS3/latest/userguide/ManageCorsUsing.html

Configure Behaviors on CloudFront Distribution

In CloudFront -> [your distribution] -> Behaviors -> Create Behavior:

  • Path Pattern: *
  • Allowed HTTP Methods: GET, HEAD, OPTIONS
  • Cached HTTP Methods: +OPTIONS
  • Origin Request Policy: Managed-CORS-S3Origin
    • This policy actually whitelists the following headers:
      • Access-Control-Request-Headers
      • Access-Control-Request-Method
      • Origin

ref:
https://aws.amazon.com/premiumsupport/knowledge-center/no-access-control-allow-origin-error/

Validate it's working:

fetch("https://metadata.perp.exchange/config.production.json")
.then((res) => res.json())
.then((out) => { console.log(out) })
.catch((err) => { throw err });
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