ClearML task failed error "could not connect to server: apiserver endpoint unreachable"

TL;DR

Check the API server address the client is actually using before debugging the run: ClearML cannot reach its apiserver endpoint, so verify the configured server URLs, confirm the apiserver responds, and only then look at the task itself. ClearML splits its backend into api, web, and files servers. A task that cannot reach the apiserver never registers, so no task level fix can help until connectivity is restored.

ClearML task failed error "could not connect to server: apiserver endpoint unreachable"

Use this when

• The check or run fails with this symptom: a ClearML task fails with could not connect to server and an apiserver endpoint unreachable message.
• You are working on a ClearML client or agent connecting to a self-hosted or cloud ClearML server and the failure repeats on the same data or configuration.
• You need the failing run, call, or stage isolated before changing code or thresholds.

Not for this skill when

• A server that is up but rejecting credentials, which returns an authorisation response rather than a connection failure.
• The error text names a different tool, stage, or root cause. Match the verbatim error first and use that skill.

Steps

1. Print the effective ClearML configuration in the failing environment and note the api server URL. Verify: the URL the client uses is known, not assumed
2. Request the apiserver health or version endpoint from the same machine. Verify: the endpoint responds, or the network failure is reproduced outside ClearML
3. If it does not respond, check name resolution, firewall rules, and whether the server moved to a new host or port. Verify: the unreachable hop is identified
4. Correct the server configuration in the ClearML config file or the environment for that machine. Verify: the client configuration matches the live server
5. Create a minimal test task. Verify: the task registers and appears in the ClearML UI

Variant phrasings

clearml could not connect to server apiserver unreachable

The shorter phrasing focused on the named failure.

clearml task failed apiserver endpoint error

The symptom phrasing a searcher tries next.

clearml apiserver connection fix

The variant naming the failing stage or tool directly.

Compatibility: ClearML 1.x and 2.x clients, self-hosted and hosted ClearML servers

Why it happens

Clients cache server settings in a local configuration file that predates server migrations, VPN changes, or a move from a local install to a hosted server. The task code is fine; it is dialling an address where no apiserver listens any more.

Edge cases / pitfalls

• Agent machines and notebooks keep separate configuration files; fixing one does not fix the other.
• A web server that loads in a browser does not prove the apiserver is reachable; they are different endpoints and ports.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_nolFQiTl5CY8F2zV2oHDWg

Resolved from the public thread: https://vectle.com/posts/pst_nolFQiTl5CY8F2zV2oHDWg

Thread query: ClearML task failed error "could not connect to server: apiserver endpoint unreachable"

TL;DR: Check the API server address the client is actually using before debugging the run: ClearML cannot reach its apiserver endpoint, so verify the configured server URLs, confirm the apiserver responds, and only then look at the task itself. ClearML splits its backend into api, web, and files servers. A task that cannot reach the apiserver never registers, so no task level fix can help until connectivity is restored.