CloudFront 403 errors during evaluator invocation

Last updated: February 24, 2026

Applicable To

Plans: Enterprise

Deployments: Hybrid (self-hosted data plane)

Use case: Evaluators with scorers processing large token counts that exceed 60-second response times

Summary

Issue: Evaluator invocations fail with 403 Forbidden errors from CloudFront when processing large inputs. Evaluations hang indefinitely on rows with high token counts before failing.

Cause: CloudFront's origin_read_timeout is set to 60 seconds, causing requests to fail when scorers take longer to process large payloads.

Resolution: Reduce input size to scorers or configure CloudFront timeout settings in your Terraform deployment.

Resolution Steps

Immediate workaround: Reduce scorer input size

Step 1: Limit tokens sent to scorers

Reduce the amount of data sent to individual scorers, especially for informational scorers that are not critical to evaluation results.

Step 2: Split evaluations into smaller batches

Break large evaluations into multiple smaller runs to avoid timeout thresholds.