What causes CANNOT_ESTABLISH_CONNECTION?

The external database server is down or unreachable from the cluster subnet. Firewall or security group rules block outbound traffic from Databricks cluster nodes to the external host. JDBC credentials are incorrect or have expired. The connection URL in the job configuration contains an incorrect hostname, port, or database name. A Unity Catalog connection object references an external data source that has changed host or credentials

How do I fix CANNOT_ESTABLISH_CONNECTION?

Test connectivity from a cluster notebook: %sh curl -v telnet:// : to verify network reachability. Verify the JDBC URL, username, and password in the job configuration or Databricks secret. Check firewall and security group rules to ensure the cluster subnet can reach the external host on the required port. For Unity Catalog connections, validate the connection object: SHOW CONNECTION . Check that the external database service is running and accepting connections

High severitysql

Power BI Refresh Error:
CANNOT_ESTABLISH_CONNECTION

What does this error mean?

Databricks SQL could not open a connection to an external data source (e.g., a JDBC database, REST endpoint, or federated catalog). The query is aborted before any data is read.

Common causes

1The external database server is down or unreachable from the cluster subnet
2Firewall or security group rules block outbound traffic from Databricks cluster nodes to the external host
3JDBC credentials are incorrect or have expired
4The connection URL in the job configuration contains an incorrect hostname, port, or database name
5A Unity Catalog connection object references an external data source that has changed host or credentials

How to fix it

1Test connectivity from a cluster notebook: %sh curl -v telnet://<host>:<port> to verify network reachability
2Verify the JDBC URL, username, and password in the job configuration or Databricks secret
3Check firewall and security group rules to ensure the cluster subnet can reach the external host on the required port
4For Unity Catalog connections, validate the connection object: SHOW CONNECTION <name>
5Check that the external database service is running and accepting connections

Frequently asked questions

Does CANNOT_ESTABLISH_CONNECTION affect Delta tables?

No — this error only affects queries connecting to external sources via JDBC, REST, or Unity Catalog federated connections. Native Delta Lake reads use cloud storage and produce different errors.

How do I test JDBC connectivity from a Databricks cluster?

Run a notebook cell with %sh to test network reachability, then use spark.read.jdbc() with a small limit to test the full connection end-to-end.