Form follows function: Building resilient form submissions at scale

Webflow emphasizes the critical role of form submissions in sales pipelines by ensuring their durability, non-blocking nature, idempotency, and operability even during system failures. To achieve this, Webflow implemented a system of write-ahead backups stored on Amazon S3 to safeguard submissions before they reach the database, ensuring they are available for replays in case of downstream outages. The replay system operates in two modes: per site replay for targeted recovery and global replay for widespread outages, using submission hashes to avoid duplicating already ingested data. This hashing system ensures each form submission is uniquely identifiable, allowing for efficient deduplication during replays and maintaining the integrity of the data pipeline by only reprocessing submissions that initially failed to save.