When an application works locally but cannot connect to its hosted database, compare the deployment configuration and connection path before changing the application. A useful diagnosis separates network reachability, authentication, database selection and schema state.
Confirm the intended engine and endpoint
Record the database engine and version required by the project. Confirm the selected hosting service supports that requirement. Use the endpoint and port supplied for the deployed environment; localhost refers to the machine or container running the application, which may not be the database host.
Check whether the application and database communicate through a local socket, a private network or an explicitly permitted remote connection. Different engines have different listener and access-control settings. Follow that engine's documentation rather than opening every database port as a general fix.
Classify the actual error
- Connection timeout or refusal: inspect the endpoint, listener and permitted network path.
- Authentication failure: verify the intended account and deployment configuration.
- Database not found: confirm the database name and creation/import step.
- Missing table or column: inspect the application's migration or schema version.
- Connection succeeds but writes fail: check permissions and application-level constraints.
Provide support with sanitised errors and configuration key names, not a password-bearing connection string. Keep a record of whether the failure occurs at startup or only when a particular action runs.
Verify a representative application action
After correcting configuration, test a safe read and a controlled write using the application. A database login from an administrator tool does not prove the deployed application uses the same credentials or endpoint. Confirm that the test affects the intended environment.
If a schema change is needed, take an appropriate backup and use the project's supported migration procedure. The backup-rehearsal and private-access guides below cover the adjacent tasks without changing the product's actual database support.