[ECR] [request]: Pull through cache for self-hosted Artifactory

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**Tell us about your request**
We use an on-prem self-hosted Artifactory instance to host container images. We currently pull directly from that for our ECS and EKR jobs. It would be better if we could use ECR's pull through cache feature to reduce load on our Artifactory instance, and reduce traffic over our Direct Connect.

To add complexity, we pull from our cache over a direct connect, so it would be important that we could use our internal network to pull from to avoid having to expose our Artifactory to the internet. Amazon Managed Grafana supports this for example (https://docs.aws.amazon.com/grafana/latest/userguide/AMG-configure-vpc.html)

**Which service(s) is this request for?**
ECR

**Tell us about the problem you're trying to solve. What are you trying to do, and why is it hard?**
Using Artifactory with a pull through cache is not possible.

**Are you currently working around this issue?**
We are currently pulling directly from our Artifactory instance

**Additional context**

**Attachments**

No repository files, tests, or entry points are mentioned. Start by reviewing the ECR pull-through cache requirements in this issue, especially support for a self-hosted Artifactory source and private-network access over Direct Connect. Done means determining whether both capabilities can be supported and defining the resulting implementation scope.

Written by the indexing model from the issue text.