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ECR is slow. Despite being a static datastore presumably backed by S3 it will only serve container image layers at around 150mbps, when dealing with large (10GB) container images this is a problem. R2 will happily serve the same data at multi-gigabit speed.

Data transfer costs. Our registry is for our customers, and they expect to pull their images from environments outside AWS, e.g. GitHub Actions.

If that customer has a 2GB image, they want to build the image and then pull it into 10 separate matrix jobs (think like parallel Cypress tests), and they have 1,000 commits in a month, then the AWS data transfer costs are $1,800/mo, just for that one customer to pull their images.

With R2, it acts both as a CDN and since Cloudflare does not charge for egress, reduces the cost to only storage + the one-time transfer out of AWS.

Cost of storage and egress cost are wildly more expensive on ECR compared to CF+R2