Summary
On a self-hosted Retool instance, running a workflow block fails with "Internal error running a block: Error: An internal server error occurred." The report includes the deployment's WORKFLOW_* environment variables (e.g., WORKFLOW_BACKEND_HOST, WORKFLOW_TEMPORAL_CLUSTER_FRONTEND_HOST/PORT).
AI Response
For self-hosted deployments, this generic error most commonly traces back to the workflow backend or Temporal host being misconfigured, so the block runner can't reach the internal workflow API. Confirm that WORKFLOW_BACKEND_HOST and the WORKFLOW_TEMPORAL_CLUSTER_FRONTEND_HOST/PORT values resolve to reachable, correctly-named hosts and that no variable is interpolating to an empty/invalid value (a hallmark symptom is requests going to a host like "null.undefined" in the worker logs). Check the workflow worker/backend container logs for the verbose FetchError to pinpoint which host is unreachable, then correct the corresponding environment variable and confirm outbound network connectivity from the workflow containers. Validating these values against the documented self-hosted workflow environment variables is the fastest path to resolution.
Sources
“Internal error running a block” when running a workflow resource query
A self-hosted + Temporal deployment hit this exact error; the resolved root cause was a misconfigured Temporal/workflow host environment variable causing requests to an invalid host, fixed by correcting the variable so it resolved properly.
Official reference for the Retool Workflows environment variables used to configure self-hosted instances, useful for validating the WORKFLOW_* and Temporal host/port values in the deployment.
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