Grafana on AWS EC2 behind Application Load Balancer, Snapshot not working

I have installed Grafana on an AWS EC2 using the latest docker image. An application load balancer serves as a reverse proxy. Everything works great - dashboards, data connections, authentication (OAuth2 to Azure AD and Github), plugin management. Except for one thing: Snapshots. I get a panel showing 403 Forbidden when trying to make both local snapshot and externally published ones.

It works though if I allow inbound connections directly to the EC2 and connect to Grafana through that route, bypassing the load balancer. Could there be something related to the root_url setting, which is altered since I’m using a custom domain name and OAuth2.

There seems to be no general connectivity issues from the EC2 (or from the Grafana docker container). curl returns what is expected I believe.

Any ideas?

Ok, I found the culprit. It was a rule set in AWS WAF (managed firewall service) that imposed a size restriction of the html body. After overriding this rule, all was fine and dandy with snapshots sharing.