I ran into something similar during deployment. Hopefully this helps with your debugging: if the agent was launched separately from the rest of the stack, it may not have proper docker-DNS resolution to None . (e.g. if in the same docker-compose, perhaps you didnt add the backend network field, or if it was launched separately through docker run without an explicit external network defined)

if the agent's on the same machine, try docker network connect to add the agent to the same backend network used by the server stack.

if your backend is publicly accessibly, you can have your agent's clearml.conf file point to a publically reachable endpoint instead of None , this is what enables my remote workers to talk to my instance hosting clearml.