How to configure an Expectation Store to use GCS

By default, newly ProfiledThe act of generating Metrics and candidate Expectations from data. ExpectationsA verifiable assertion about data. are stored as Expectation SuitesA collection of verifiable assertions about data. in JSON format in the expectations/ subdirectory of your great_expectations/ folder. This guide will help you configure Great Expectations to store them in a Google Cloud Storage (GCS) bucket.

Prerequisites: This how-to guide assumes you have:

• Completed the Getting Started Tutorial
• Have a working installation of Great Expectations
• Configured a Data Context.
• Configured an Expectations Suite.
• Configured a Google Cloud Platform (GCP) service account with credentials that can access the appropriate GCP resources, which include Storage Objects.
• Identified the GCP project, GCS bucket, and prefix where Expectations will be stored.

Steps

1. Configure your GCP credentials

Check that your environment is configured with the appropriate authentication credentials needed to connect to the GCS bucket where Expectations will be stored.

The Google Cloud Platform documentation describes how to verify your authentication for the Google Cloud API, which includes:

1. Creating a Google Cloud Platform (GCP) service account,
2. Setting the GOOGLE_APPLICATION_CREDENTIALS environment variable,
3. Verifying authentication by running a simple Google Cloud Storage client library script.

2. Identify your Data Context Expectations Store

In your great_expectations.yml, look for the following lines. The configuration tells Great Expectations to look for Expectations in a StoreA connector to store and retrieve information about metadata in Great Expectations. called expectations_store. The base_directory for expectations_store is set to expectations/ by default.

stores:
  expectations_store:
    class_name: ExpectationsStore
    store_backend:
      class_name: TupleFilesystemStoreBackend
      base_directory: expectations/

expectations_store_name: expectations_store

3. Update your configuration file to include a new store for Expectations on GCS

In our case, the name is set to expectations_GCS_store, but it can be any name you like. We also need to make some changes to the store_backend settings. The class_name will be set to TupleGCSStoreBackend, project will be set to your GCP project, bucket will be set to the address of your GCS bucket, and prefix will be set to the folder on GCS where Expectation files will be located.

danger

If you are also storing Validations in GCS or DataDocs in GCS, please ensure that the prefix values are disjoint and one is not a substring of the other.

stores:
  expectations_GCS_store:
    class_name: ExpectationsStore
    store_backend:
      class_name: TupleGCSStoreBackend
      project: <YOUR GCP PROJECT NAME>
      bucket: <YOUR GCS BUCKET NAME>
      prefix: <YOUR GCS PREFIX NAME>

expectations_store_name: expectations_GCS_store

4. Copy existing Expectation JSON files to the GCS bucket (This step is optional)

One way to copy Expectations into GCS is by using the gsutil cp command, which is part of the Google Cloud SDK. The following example will copy one Expectation, my_expectation_suite from a local folder to the GCS bucket. Information on other ways to copy Expectation JSON files, like the Cloud Storage browser in the Google Cloud Console, can be found in the Documentation for Google Cloud.

gsutil cp expectations/my_expectation_suite.json gs://<YOUR GCS BUCKET NAME>/<YOUR GCS PREFIX NAME>/my_expectation_suite.json

Operation completed over 1 objects

5. Confirm that the new Expectations store has been added

Run the following:

great_expectations store list

Only the active Stores will be listed. Great Expectations will look for Expectations in GCS as long as we set the expectations_store_name variable to expectations_GCS_store, and the config for expectations_store can be removed if you would like.

- name: expectations_GCS_store
    class_name: ExpectationsStore
    store_backend:
      class_name: TupleGCSStoreBackend
      project: <YOUR GCP PROJECT NAME>
      bucket: <YOUR GCS BUCKET NAME>
      prefix: <YOUR GCS PREFIX NAME>

6. Confirm that Expectations can be accessed from GCS

To do this, run the following:

great_expectations suite list

If you followed Step 4, the output should include the Expectation we copied to GCS: my_expectation_suite. If you did not copy Expectations to the new Store, you will see a message saying no Expectations were found.

1 Expectation Suite found:
 - my_expectation_suite

Additional Notes

To view the full script used in this page, see it on GitHub:

• how_to_configure_an_expectation_store_in_gcs.py