Connecting data

Key principle: network accessibilityKey principle: network accessibility

Before you create a connection in the DataLens UI, always consider this question: Can the DataLens server access the database server over the network?

Network restrictions account for 90% of connection issues:

• Firewall: Blocks the port at the database server or network equipment.

• Security groups: In cloud environments, security group rules deny incoming traffic from DataLens VMs.

• Incorrect host or port: There is a typo in the connection credentials.

How to troubleshoot issuesHow to troubleshoot issues

Use the control-api pod to check accessibility with curl or telnet:

# Connect to the `control_api` pod
./init.sh --kubectl exec -it <control-api-pod-name> -- /bin/bash

# Check access to your host and port
curl -v telnet://my-postgres-db.internal:5432

Check pod logs for information on the Connection timeout. To do this, run the following command:

 ./init.sh --stern --tail 100 --no-follow pod/<control-api-pod-name>

Creating a basic connectionCreating a basic connection

This is a basic use case. To create a connection, the user needs the Editor or Admin role.

1. In the DataLens UI, go to Connections and click Create connection.

2. Select a source type, e.g., PostgreSQL.

3. Fill in these fields: host name, port, database name, username, and password.

4. Click Check connection. If successful, save the configuration.

Passwords and tokens you enter in the above fields are encrypted using CONTROL_API_CRYPTO_KEY, one of the two cryptographic key types used in DataLens. This key is used to encrypt sensitive data (passwords or tokens) in connection fields. It is generated and saved automatically.

Connecting to a database with TLS encryptionConnecting to a database with TLS encryption

In corporate environments, TLS is often used for secure transfer of data. If a database uses a certificate signed by an internal certificate authority (CA), DataLens will not trust it by default.

To resolve this, add the root CA certificate to the DataLens trust store. You need to do this at the Kubernetes configuration level by updating values.yaml to add the CA to the system trust store.

Once trust is configured, you can enable TLS in the connection settings and specify the relevant properties.

Configuring and using file connectionsConfiguring and using file connections

To work with files, first enable the files feature in values.yaml.

Workflow for users:

1. Create a File-type connection.

2. Upload a CSV or XLS file.

3. This file is saved to the internal S3 storage (MinIO), and then its contents is pushed to ClickHouse.

4. DataLens automatically creates a dataset over the resulting ClickHouse table.

Connector featuresConnector features

JSON APIJSON API

It enables connections to data sources which send JSON over HTTP. The connector is used together with Chart Editor to rapidly build charts from software sources.

Trino (formerly PrestoSQL)Trino (formerly PrestoSQL)

Not a database but a federated query engine, Trino enables you to run a single SQL query to data residing in different systems, e.g., join PostgreSQL and S3 data in one query. DataLens connects to Trino, and Trino, to the end sources.

Use caseUse case

A user reports their connection to Greenplum fails with the Connection timed out error. What is your first troubleshooting step?

• Restart the control-api pod
• Check the user's password
• Check network access from the control-api pod to the Greenplum host and port
• Ask the user to check their SQL query

Hands-on task: Creating a file-based connectionHands-on task: Creating a file-based connection

1. Ensure the files feature is enabled in your values.yaml:

   features:
     files:
       enabled: true
   

   If not, enable it and apply this configuration: ./init.sh --values <your_file>.yaml.

2. Create a simple sales.csv file on your local computer:

   City,Sales
   Moscow,1500
   

Paris,1200
London,1800

1. In the DataLens UI, create a new **File** connection.

1. Upload `sales.csv` and wait for it to get processed.

1. Upon successful upload, you see a data preview window. Click **Create** in the top right corner.

## Summary

You have reviewed one of the most common administrator tasks: ensuring data connectivity. Now you can create basic and file-based connections and configure TLS properly.