Using lakeFS with the Unity Catalog

Overview

Databricks Unity Catalog serves as a centralized data governance platform for your data lakes. Through the Unity Catalog, you can search for and locate data assets across workspaces via a unified catalog. Leveraging the external tables feature within Unity Catalog, you can register a Delta Lake table exported from lakeFS and access it through the unified catalog. The subsequent step-by-step guide will lead you through the process of configuring a Lua hook that exports Delta Lake tables from lakeFS, and subsequently registers them in Unity Catalog.

Currently, Unity Catalog export feature exclusively supports AWS S3 as the underlying storage solution. It’s planned to support other cloud providers soon.

Prerequisites

Before starting, ensure you have the following:

1. Access to Unity Catalog
2. An active lakeFS installation with S3 as the backing storage, and a repository in this installation.
3. A Databricks SQL warehouse.
4. AWS Credentials with S3 access.
5. lakeFS credentials with access to your Delta Tables.

Supported from lakeFS v1.4.0

Databricks authentication

Given that the hook will ultimately register a table in Unity Catalog, authentication with Databricks is imperative. Make sure that:

1. You have a Databricks Service Principal.
2. The Service principal has token usage permissions, and an associated token configured.
3. The service principal has the Service principal: Manager privilege over itself (Workspace: Admin console -> Service principals -> <service principal> -> Permissions -> Grant access (<service principal>: Service principal: Manager), with Workspace access and Databricks SQL access checked (Admin console -> Service principals -> <service principal> -> Configurations).
4. Your SQL warehouse allows the service principal to use it (SQL Warehouses -> <SQL warehouse> -> Permissions -> <service principal>: Can use).
5. The catalog grants the USE CATALOG, USE SCHEMA, CREATE SCHEMA permissions to the service principal(Catalog -> <catalog name> -> Permissions -> Grant -> <service principal>: USE CATALOG, USE SCHEMA, CREATE SCHEMA).
6. You have an External Location configured, and the service principal has the CREATE EXTERNAL TABLE permission over it (Catalog -> External Data -> External Locations -> Create location).

Guide

Table descriptor definition

To guide the Unity Catalog exporter in configuring the table in the catalog, define its properties in the Delta Lake table descriptor. The table descriptor should include (at minimum) the following fields:

1. name: The table name.
2. type: Should be delta.
3. catalog: The name of the catalog in which the table will be created.
4. path: The path in lakeFS (starting from the root of the branch) in which the Delta Lake table’s data is found.

Let’s define the table descriptor and upload it to lakeFS:

Save the following as famous-people-td.yaml:

---
name: famous_people
type: delta
catalog: my-catalog-name
path: tables/famous-people

It’s recommended to create a Unity catalog with the same name as your repository

Upload the table descriptor to _lakefs_tables/famous-people-td.yaml and commit:

lakectl fs upload lakefs://repo/main/_lakefs_tables/famous-people-td.yaml -s ./famous-people-td.yaml && \
lakectl commit lakefs://repo/main -m "add famous people table descriptor"

Write some data

Insert data into the table path, using your preferred method (e.g. Spark), and commit upon completion.

We shall use Spark and lakeFS’s S3 gateway to write some data as a Delta table:

pyspark --packages "io.delta:delta-spark_2.12:3.0.0,org.apache.hadoop:hadoop-aws:3.3.4,com.amazonaws:aws-java-sdk-bundle:1.12.262" \
  --conf spark.sql.extensions=io.delta.sql.DeltaSparkSessionExtension \
  --conf spark.sql.catalog.spark_catalog=org.apache.spark.sql.delta.catalog.DeltaCatalog \
  --conf spark.hadoop.fs.s3a.aws.credentials.provider='org.apache.hadoop.fs.s3a.SimpleAWSCredentialsProvider' \
  --conf spark.hadoop.fs.s3a.endpoint='<LAKEFS_SERVER_URL>' \
  --conf spark.hadoop.fs.s3a.access.key='<LAKEFS_ACCESS_KEY>' \
  --conf spark.hadoop.fs.s3a.secret.key='<LAKEFS_SECRET_ACCESS_KEY>' \
  --conf spark.hadoop.fs.s3a.path.style.access=true

data = [
   ('James','Bond','England','intelligence'),
   ('Robbie','Williams','England','music'),
   ('Hulk','Hogan','USA','entertainment'),
   ('Mister','T','USA','entertainment'),
   ('Rafael','Nadal','Spain','professional athlete'),
   ('Paul','Haver','Belgium','music'),
]
columns = ["firstname","lastname","country","category"]
df = spark.createDataFrame(data=data, schema = columns)
df.write.format("delta").mode("overwrite").partitionBy("category", "country").save("s3a://repo/main/tables/famous-people")

The Unity Catalog exporter script

For code references check delta_exporter and unity_exporter docs.

Create unity_exporter.lua:

local aws = require("aws")
local formats = require("formats")
local databricks = require("databricks")
local delta_export = require("lakefs/catalogexport/delta_exporter")
local unity_export = require("lakefs/catalogexport/unity_exporter")

local sc = aws.s3_client(args.aws.access_key_id, args.aws.secret_access_key, args.aws.region)

-- Export Delta Lake tables export:
local delta_client = formats.delta_client(args.lakefs.access_key_id, args.lakefs.secret_access_key, args.aws.region)
local delta_table_details = delta_export.export_delta_log(action, args.table_defs, sc.put_object, delta_client, "_lakefs_tables")

-- Register the exported table in Unity Catalog:
local databricks_client = databricks.client(args.databricks_host, args.databricks_token)
local registration_statuses = unity_export.register_tables(action, "_lakefs_tables", delta_table_details, databricks_client, args.warehouse_id)

for t, status in pairs(registration_statuses) do
    print("Unity catalog registration for table \"" .. t .. "\" completed with commit schema status : " .. status .. "\n")
end

Upload the lua script to the main branch under scripts/unity_exporter.lua and commit:

lakectl fs upload lakefs://repo/main/scripts/unity_exporter.lua -s ./unity_exporter.lua && \
lakectl commit lakefs://repo/main -m "upload unity exporter script"

Action configuration

Define an action configuration that will run the above script after a commit is completed (post-commit) over the main branch.

Create unity_exports_action.yaml:

---
name: unity_exports
on:
  post-commit:
     branches: ["main"]
hooks:
  - id: unity_export
    type: lua
    properties:
      script_path: scripts/unity_exporter.lua
      args:
        aws:
          access_key_id: <AWS_ACCESS_KEY_ID>
          secret_access_key: <AWS_SECRET_ACCESS_KEY>
          region: <AWS_REGION>
        lakefs: # provide credentials of a user that has access to the script and Delta Table
          access_key_id: <LAKEFS_ACCESS_KEY_ID> 
          secret_access_key: <LAKEFS_SECRET_ACCESS_KEY>
        table_defs: # an array of table descriptors used to be defined in Unity Catalog
          - famous-people-td
        databricks_host: <DATABRICKS_HOST_URL>
        databricks_token: <DATABRICKS_SERVICE_PRINCIPAL_TOKEN>
        warehouse_id: <WAREHOUSE_ID>

Upload the action configurations to _lakefs_actions/unity_exports_action.yaml and commit:

Once the commit will finish its run, the action will start running since we’ve configured it to run on post-commit events on the main branch.

lakectl fs upload lakefs://repo/main/_lakefs_actions/unity_exports_action.yaml -s ./unity_exports_action.yaml && \
lakectl commit lakefs://repo/main -m "upload action and run it"

The action has run and exported the famous_people Delta Lake table to the repo’s storage namespace, and has register the table as an external table in Unity Catalog under the catalog my-catalog-name, schema main (as the branch’s name) and table name famous_people: my-catalog-name.main.famous_people.

Databricks Integration

After registering the table in Unity, you can leverage your preferred method to query the data from the exported table under my-catalog-name.main.famous_people, and view it in the Databricks’s Catalog Explorer, or retrieve it using the Databricks CLI with the following command:

databricks tables get my-catalog-name.main.famous_people