How to configure an Expectation store in GCS

By default, newly profiled Expectations are stored 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 that you have already:

  • 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 store called expectations_store. The base_directory for expectations_store is set to expectations/ by default.

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

    Warning

    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.

    expectations_store_name: expectations_GCS_store
    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_folder_name>'
    
  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, exp1 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 exp1.json gs://'<your_GCS_bucket_name>'/'<your_GCS_folder_name>'
    
    Operation completed over 1 objects/58.8 KiB.
    
  5. Confirm that the new Expectations store has been added by running great_expectations store list.

    Notice the output contains two Expectation stores: the original expectations_store on the local filesystem and the expectations_GCS_store we just configured. This is ok, since 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.

    great_expectations store list
    
    - name: expectations_store
    class_name: ExpectationsStore
    store_backend:
        class_name: TupleFilesystemStoreBackend
        base_directory: expectations/
    
    - 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_folder_name>'
    
  6. Confirm that Expectations can be accessed from GCS by running great_expectations suite list.

    If you followed Step 4, the output should include the Expectation we copied to GCS: exp1. If you did not copy Expectations to the new Store, you will see a message saying no Expectations were found.

    great_expectations suite list
    
    1 Expectation Suite found:
     - exp1
    

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