Refreshing external tables automatically for Amazon S3¶

Step 1: Configure access permissions for the S3 bucket¶

Step 2: Create the IAM Role in AWS¶

To configure access permissions for Snowflake in the AWS Management Console, do the following:

1. From the left-hand navigation pane in the Identity and Access Management (IAM) Dashboard, select Roles.

2. Select Create role.

3. Select AWS account as the trusted entity type.

4. Select Another AWS account

   

5. In the Account ID field, enter your own AWS account ID temporarily. Later, you modify the trust relationship and grant access to Snowflake.

6. Select the Require external ID option. An external ID is used to grant access to your AWS resources (such as S3 buckets) to a third party like Snowflake.

   Enter a placeholder ID such as 0000. In a later step, you will modify the trust relationship for your IAM role and specify the external ID for your storage integration.

7. Select Next.

8. Select the policy you created in Step 1: Configure Access Permissions for the S3 Bucket (in this topic).

9. Select Next.

   

10. Enter a name and description for the role, then select Create role.

    You have now created an IAM policy for a bucket, created an IAM role, and attached the policy to the role.

11. On the role summary page, locate and record the Role ARN value. In the next step, you will create a Snowflake integration that references this role.

Step 3: Create a Cloud Storage Integration in Snowflake¶

Create a storage integration using the CREATE STORAGE INTEGRATION command. A storage integration is a Snowflake object that stores a generated identity and access management (IAM) user for your S3 cloud storage, along with an optional set of allowed or blocked storage locations (i.e. buckets). Cloud provider administrators in your organization grant permissions on the storage locations to the generated user. This option allows users to avoid supplying credentials when creating stages or loading data.

A single storage integration can support multiple external (i.e. S3) stages. The URL in the stage definition must align with the S3 buckets (and optional paths) specified for the STORAGE_ALLOWED_LOCATIONS parameter.

CREATE STORAGE INTEGRATION <integration_name>
  TYPE = EXTERNAL_STAGE
  STORAGE_PROVIDER = 'S3'
  ENABLED = TRUE
  STORAGE_AWS_ROLE_ARN = '<iam_role>'
  STORAGE_ALLOWED_LOCATIONS = ('<protocol>://<bucket>/<path>/', '<protocol>://<bucket>/<path>/')
  [ STORAGE_BLOCKED_LOCATIONS = ('<protocol>://<bucket>/<path>/', '<protocol>://<bucket>/<path>/') ]

Where:

• integration_name is the name of the new integration.

• iam_role is the Amazon Resource Name (ARN) of the role you created in Step 2: Create the IAM Role in AWS (in this topic).

• protocol is one of the following:

  • s3 refers to S3 storage in public AWS regions outside of China.

  • s3china refers to S3 storage in public AWS regions in China.

  • s3gov refers to S3 storage in government regions.

• bucket is the name of a S3 bucket that stores your data files (e.g. mybucket). The required STORAGE_ALLOWED_LOCATIONS parameter and optional STORAGE_BLOCKED_LOCATIONS parameter restrict or block access to these buckets, respectively, when stages that reference this integration are created or modified.

• path is an optional path that can be used to provide granular control over objects in the bucket.

The following example creates an integration that allows access to all buckets in the account but blocks access to the defined sensitivedata folders.

Additional external stages that also use this integration can reference the allowed buckets and paths:

CREATE STORAGE INTEGRATION s3_int
  TYPE = EXTERNAL_STAGE
  STORAGE_PROVIDER = 'S3'
  ENABLED = TRUE
  STORAGE_AWS_ROLE_ARN = 'arn:aws:iam::001234567890:role/myrole'
  STORAGE_ALLOWED_LOCATIONS = ('*')
  STORAGE_BLOCKED_LOCATIONS = ('s3://mybucket1/mypath1/sensitivedata/', 's3://mybucket2/mypath2/sensitivedata/');

Step 4: Retrieve the AWS IAM User for your Snowflake Account¶

1. To retrieve the ARN for the IAM user that was created automatically for your Snowflake account, use the DESCRIBE INTEGRATION.

   DESC INTEGRATION <integration_name>;
   

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   Where:

   • integration_name is the name of the integration you created in Step 3: Create a Cloud Storage Integration in Snowflake (in this topic).

   For example:

   DESC INTEGRATION s3_int;
   

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   +---------------------------+---------------+--------------------------------------------------------------------------------+------------------+
   | property                  | property_type | property_value                                                                 | property_default |
   +---------------------------+---------------+--------------------------------------------------------------------------------+------------------|
   | ENABLED                   | Boolean       | true                                                                           | false            |
   | STORAGE_ALLOWED_LOCATIONS | List          | s3://mybucket1/mypath1/,s3://mybucket2/mypath2/                                | []               |
   | STORAGE_BLOCKED_LOCATIONS | List          | s3://mybucket1/mypath1/sensitivedata/,s3://mybucket2/mypath2/sensitivedata/    | []               |
   | STORAGE_AWS_IAM_USER_ARN  | String        | arn:aws:iam::123456789001:user/abc1-b-self1234                                 |                  |
   | STORAGE_AWS_ROLE_ARN      | String        | arn:aws:iam::001234567890:role/myrole                                          |                  |
   | STORAGE_AWS_EXTERNAL_ID   | String        | MYACCOUNT_SFCRole=2_a123456/s0aBCDEfGHIJklmNoPq=                               |                  |
   +---------------------------+---------------+--------------------------------------------------------------------------------+------------------+
   

2. Record the values for the following properties:

   Property	Description
   STORAGE_AWS_IAM_USER_ARN	The AWS IAM user created for your Snowflake account; for example, arn:aws:iam::123456789001:user/abc1-b-self1234. Snowflake provisions a single IAM user for your entire Snowflake account. All S3 storage integrations in your account use that IAM user.
   STORAGE_AWS_EXTERNAL_ID	The external ID that Snowflake uses to establish a trust relationship with AWS. If you didn’t specify an external ID (STORAGE_AWS_EXTERNAL_ID) when you created the storage integration, Snowflake generates an ID for you to use.

   You provide these values in the next section.

Step 5: Grant the IAM User Permissions to Access Bucket Objects¶

The following step-by-step instructions describe how to configure IAM access permissions for Snowflake in your AWS Management Console so that you can use a S3 bucket to load and unload data:

1. Log in to the AWS Management Console.

2. Select IAM.

3. From the left-hand navigation pane, select Roles.

4. Select the role you created in Step 2: Create the IAM Role in AWS (in this topic).

5. Select the Trust relationships tab.

6. Select Edit trust policy.

7. Modify the policy document with the DESC STORAGE INTEGRATION output values you recorded in Step 4: Retrieve the AWS IAM User for your Snowflake Account (in this topic):

   Policy document for IAM role

   {
     "Version": "2012-10-17",
     "Statement": [
       {
         "Sid": "",
         "Effect": "Allow",
         "Principal": {
           "AWS": "<snowflake_user_arn>"
         },
         "Action": "sts:AssumeRole",
         "Condition": {
           "StringEquals": {
             "sts:ExternalId": "<snowflake_external_id>"
           }
         }
       }
     ]
   }
   

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   Where:

   • snowflake_user_arn is the STORAGE_AWS_IAM_USER_ARN value you recorded.

   • snowflake_external_id is the STORAGE_AWS_EXTERNAL_ID value you recorded.

     In this example, the snowflake_external_id value is MYACCOUNT_SFCRole=2_a123456/s0aBCDEfGHIJklmNoPq=.

     Note

     For security reasons, if you create a new storage integration (or recreate an existing storage integration using the CREATE OR REPLACE STORAGE INTEGRATION syntax) without specifying an external ID, the new integration has a different external ID and can’t resolve the trust relationship unless you update the trust policy.

8. Select Update policy to save your changes.

Step 1: Create a stage (if needed)¶

Create an external stage that references your S3 bucket using the CREATE STAGE command. Snowflake reads your staged data files into the external table metadata. Alternatively, you can use an existing external stage.

The following example creates a stage named mystage in the active schema for the user session. The cloud storage URL includes the path files. The stage references a storage integration named my_storage_int.

USE SCHEMA mydb.public;

CREATE STAGE mystage
  URL = 's3://mybucket/files'
  STORAGE_INTEGRATION = my_storage_int;

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Step 2: Create an external table¶

Create an external table using the CREATE EXTERNAL TABLE command. For example, create an external table in the mydb.public schema that reads JSON data from staged files.

The stage reference includes a folder path named path1. The external table appends this path to the stage definition, i.e. the external table references the data files in @mystage/files/path1.

Note that the AUTO_REFRESH parameter is TRUE by default:

CREATE OR REPLACE EXTERNAL TABLE ext_table
 WITH LOCATION = @mystage/path1/
 FILE_FORMAT = (TYPE = JSON);

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Step 3: Configure event notifications¶

Configure event notifications for your S3 bucket to notify Snowflake when new or updated data is available to read into the external table metadata. The auto-refresh feature relies on SQS queues to deliver event notifications from S3 to Snowflake.

For ease of use, these SQS queues are created and managed by Snowflake. The SHOW EXTERNAL TABLES command output displays the Amazon Resource Name (ARN) of your SQS queue.

1. Execute the SHOW EXTERNAL TABLES command:

   SHOW EXTERNAL TABLES;
   

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   Note the ARN of the SQS queue for the external table in the notification_channel column. Copy the ARN to a convenient location.

   Note

   Following AWS guidelines, Snowflake designates no more than one SQS queue per S3 bucket. This SQS queue may be shared among multiple buckets in the same AWS account. The SQS queue coordinates notifications for all external tables reading data files from the same S3 bucket. When a new or modified data file is uploaded into the bucket, all external table definitions that match the stage directory path read the file details into their metadata.

2. Log into the AWS Management Console.

3. Configure an event notification for your S3 bucket using the instructions provided in the Amazon S3 documentation. Complete the fields as follows:

   • Name: Name of the event notification (e.g. Auto-ingest Snowflake).

   • Events: Select the ObjectCreate (All) and ObjectRemoved options.

   • Send to: Select SQS Queue from the dropdown list.

   • SQS: Select Add SQS queue ARN from the dropdown list.

   • SQS queue ARN: Paste the SQS queue name from the SHOW EXTERNAL TABLES output.

The external stage with auto-refresh is now configured!

When new or updated data files are added to the S3 bucket, the event notification informs Snowflake to scan them into the external table metadata.

Step 4: Manually refresh external table metadata¶

Manually refresh the external table metadata once using ALTER EXTERNAL TABLE with the REFRESH parameter, e.g.:

ALTER EXTERNAL TABLE ext_table REFRESH;

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This ensures the metadata is synchronized with any changes to the file list that occurred since Step 2. Thereafter, the S3 event notifications trigger the metadata refresh automatically.

Step 5: Configure security¶

For each additional role that will be used to query the external table, grant sufficient access control privileges on the various objects (i.e. the database(s), schema(s), stage, and table) using GRANT <privileges>:

Prerequisite: Create an Amazon SNS Topic and Subscription¶

1. Create an SNS topic in your AWS account to handle all messages for the Snowflake stage location on your S3 bucket.

2. Subscribe your target destinations for the S3 event notifications (e.g. other SQS queues or AWS Lambda workloads) to this topic. SNS publishes event notifications for your bucket to all subscribers to the topic.

For instructions, see the SNS documentation.

Step 1: Subscribe the Snowflake SQS Queue to the SNS Topic¶

1. Log into the AWS Management Console.

2. From the home dashboard, choose Simple Notification Service (SNS).

3. Choose Topics from the left-hand navigation pane.

4. Locate the topic for your S3 bucket. Note the topic ARN.

5. Using a Snowflake client, query the SYSTEM$GET_AWS_SNS_IAM_POLICY system function with your SNS topic ARN:

   select system$get_aws_sns_iam_policy('<sns_topic_arn>');
   

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   The function returns an IAM policy that grants a Snowflake SQS queue permission to subscribe to the SNS topic.

   For example:

   select system$get_aws_sns_iam_policy('arn:aws:sns:us-west-2:001234567890:s3_mybucket');
   
   +---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | SYSTEM$GET_AWS_SNS_IAM_POLICY('ARN:AWS:SNS:US-WEST-2:001234567890:S3_MYBUCKET')                                                                                                                                                                   |
   +---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | {"Version":"2012-10-17","Statement":[{"Sid":"1","Effect":"Allow","Principal":{"AWS":"arn:aws:iam::123456789001:user/vj4g-a-abcd1234"},"Action":["sns:Subscribe"],"Resource":["arn:aws:sns:us-west-2:001234567890:s3_mybucket"]}]}                 |
   +---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
   

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6. Return to the AWS Management Console. Choose Topics from the left-hand navigation pane.

7. Select the topic for your S3 bucket, and click the Edit button. The Edit page opens.

8. Click Access policy - Optional to expand this area of the page.

9. Merge the IAM policy addition from the SYSTEM$GET_AWS_SNS_IAM_POLICY function results into the JSON document.

   For example:

   Original IAM policy (abbreviated):

   {
     "Version":"2008-10-17",
     "Id":"__default_policy_ID",
     "Statement":[
        {
           "Sid":"__default_statement_ID",
           "Effect":"Allow",
           "Principal":{
              "AWS":"*"
           }
           ..
        }
      ]
    }
   

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   Merged IAM policy:

   {
     "Version":"2008-10-17",
     "Id":"__default_policy_ID",
     "Statement":[
        {
           "Sid":"__default_statement_ID",
           "Effect":"Allow",
           "Principal":{
              "AWS":"*"
           }
           ..
        },
        {
           "Sid":"1",
           "Effect":"Allow",
           "Principal":{
             "AWS":"arn:aws:iam::123456789001:user/vj4g-a-abcd1234"
            },
            "Action":[
              "sns:Subscribe"
            ],
            "Resource":[
              "arn:aws:sns:us-west-2:001234567890:s3_mybucket"
            ]
        }
      ]
    }
   

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10. Add an additional policy grant to allow S3 to publish event notifications for the bucket to the SNS topic.

    For example (using the SNS topic ARN and S3 bucket used throughout these instructions):

    {
        "Sid":"s3-event-notifier",
        "Effect":"Allow",
        "Principal":{
           "Service":"s3.amazonaws.com"
        },
        "Action":"SNS:Publish",
        "Resource":"arn:aws:sns:us-west-2:001234567890:s3_mybucket",
        "Condition":{
           "ArnLike":{
              "aws:SourceArn":"arn:aws:s3:*:*:s3_mybucket"
           }
        }
     }
    

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    Merged IAM policy:

    {
      "Version":"2008-10-17",
      "Id":"__default_policy_ID",
      "Statement":[
         {
            "Sid":"__default_statement_ID",
            "Effect":"Allow",
            "Principal":{
               "AWS":"*"
            }
            ..
         },
         {
            "Sid":"1",
            "Effect":"Allow",
            "Principal":{
              "AWS":"arn:aws:iam::123456789001:user/vj4g-a-abcd1234"
             },
             "Action":[
               "sns:Subscribe"
             ],
             "Resource":[
               "arn:aws:sns:us-west-2:001234567890:s3_mybucket"
             ]
         },
         {
            "Sid":"s3-event-notifier",
            "Effect":"Allow",
            "Principal":{
               "Service":"s3.amazonaws.com"
            },
            "Action":"SNS:Publish",
            "Resource":"arn:aws:sns:us-west-2:001234567890:s3_mybucket",
            "Condition":{
               "ArnLike":{
                  "aws:SourceArn":"arn:aws:s3:*:*:s3_mybucket"
               }
            }
          }
       ]
     }
    

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11. Click the Save changes button.

Step 2: Create a stage (if needed)¶

Create an external stage that references your S3 bucket using the CREATE STAGE command. Snowflake reads your staged data files into the external table metadata.

Alternatively, you can use an existing external stage.

The following example creates a stage named mystage in the active schema for the user session. The cloud storage URL includes the path files. The stage references a storage integration named my_storage_int:

USE SCHEMA mydb.public;

CREATE STAGE mystage
  URL = 's3://mybucket/files'
  STORAGE_INTEGRATION = my_storage_int;

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Step 3: Create an external table¶

Create an external table using CREATE EXTERNAL TABLE. Identify the SNS topic ARN from Prerequisite: Create an Amazon SNS Topic and Subscription.

CREATE EXTERNAL TABLE <table_name>
 ..
 AWS_SNS_TOPIC = '<sns_topic_arn>';

Where:

AWS_SNS_TOPIC = '<sns_topic_arn>'

Specifies the ARN for the SNS topic for your S3 bucket. The CREATE EXTERNAL TABLE statement subscribes the Snowflake SQS queue to the specified SNS topic.

For example, create an external table in the mydb.public schema that reads JSON data from staged files. The stage reference includes a folder path named path1. The external table appends this path to the stage definition, i.e. the external table references the data files in @mystage/files/path1. Note that the AUTO_REFRESH parameter is TRUE by default:

CREATE EXTERNAL TABLE ext_table
 WITH LOCATION = @mystage/path1/
 FILE_FORMAT = (TYPE = JSON)
 AWS_SNS_TOPIC = 'arn:aws:sns:us-west-2:001234567890:s3_mybucket';

To remove this parameter from an external table, it is necessary currently to recreate the external table using the CREATE OR REPLACE EXTERNAL TABLE syntax.

Step 4: Manually refresh external table metadata¶

Manually refresh the external table metadata once using ALTER EXTERNAL TABLE with the REFRESH parameter, e.g.:

ALTER EXTERNAL TABLE ext_table REFRESH;

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This ensures the metadata is synchronized with any changes to the file list that occurred since Step 3. Thereafter, the S3 event notifications trigger the metadata refresh automatically.

Step 5: Configure security¶

For each additional role that will be used to query the external table, grant sufficient access control privileges on the various objects (i.e. the database(s), schema(s), stage, and table) using GRANT <privileges>: