I had the problem described in this ticket. In short:
I set up a Docker Swarm Stack with Loki and Grafana and got “Bad Gateway. 502” when trying to add Loki as data source in Grafana.
I could solve it by changing the stack configuration of the Loki service from:
ports: - "3100:3100"
ports: - target: 3100 published: 3100 mode: host
Does anyone know why its not working with the default Docker Swarm load balancer? Is there some Docker configuration necessary to make it work or is this a bug in Loki/Grafana?