Recurly, a software-as-a-service (SaaS) billing management platform, enables businesses to process payments across several payment channels.

Delta Lake is an open source storage layer that sits on top of existing data lake file storage, such AWS S3, Azure Data Lake Storage, or HDFS. It uses versioned Apache Parquet files to store data, and a transaction log to keep track of commits, to provide capabilities like ACID transactions, data versioning, and audit history.

Recurly uses a REST API to allow developers to get data out of the service. The API supports endpoints for billing information, coupons, plans, invoices, and more.

To get a list of Recurly accounts for a given subdomain, you could call GET /v2/accounts, with any of seven optional parameters for selecting and sorting the output.

Results of Recurly API calls are returned as XML files. An XML file returned from a "list accounts" call to the Recurly API might look like this:

<account href="https://your-subdomain.recurly.com/v2/accounts/1">
  <adjustments href="https://your-subdomain.recurly.com/v2/accounts/1/adjustments"/>
  <billing_info href="https://your-subdomain.recurly.com/v2/accounts/1/billing_info"/>
  <invoices href="https://your-subdomain.recurly.com/v2/accounts/1/invoices"/>
  <redemptions href="https://your-subdomain.recurly.com/v2/accounts/1/redemptions"/>
  <subscriptions href="https://your-subdomain.recurly.com/v2/accounts/1/subscriptions"/>
  <transactions href="https://your-subdomain.recurly.com/v2/accounts/1/transactions"/>
  <account_code>1</account_code>
  <state>active</state>
  <username>verena1234</username>
  <email>verena@example.com</email>
  <cc_emails>bob@example.com,susan@example.com</cc_emails>
  <first_name>Verena</first_name>
  <last_name>Example</last_name>
  <company_name>New Company Name</company_name>
  <vat_number nil="nil"/>
  <tax_exempt type="boolean">false</tax_exempt>
  <address>
    <address1>123 Main St.</address1>
    <address2 nil="nil"/>
    <city>Philadelphia</city>
    <state>PA</state>
    <zip>19107</zip>
    <country>US</country>
    <phone nil="nil"/>
  </address>
  <accept_language nil="nil"/>
  <has_live_subscription type="boolean">true</has_live_subscription>
  <has_active_subscription type="boolean">true</has_active_subscription>
  <has_future_subscription type="boolean">false</has_future_subscription>
  <has_canceled_subscription type="boolean">false</has_canceled_subscription>
  <has_past_due_invoice type="boolean">false</has_past_due_invoice>
  <hosted_login_token>96e74bd5e14d18e6da463a0d638a2621</hosted_login_token>
  <created_at type="datetime">2017-12-08T20:59:43Z</created_at>
  <updated_at type="datetime">2017-12-11T17:56:24Z</updated_at>
  <closed_at nil="nil"/>
</account>

If you don't already have a data structure in which to store the data you retrieve, you'll have to create a schema for your data tables. Then, for each value in the response, you'll need to identify a predefined datatype (INTEGER, DATETIME, etc.) and build a table that can receive them. Recurly's documentation should tell you what fields are provided by each endpoint, along with their corresponding datatypes.

Complicating things is the fact that the records retrieved from the source may not always be "flat" – some of the objects may actually be lists. This means you'll likely have to create additional tables to capture the unpredictable cardinality in each record.

To create a Delta table, you can use existing Apache Spark SQL code and change the format from parquet, csv, or json to delta. Once you have a Delta table, you can write data into it using Apache Spark's Structured Streaming API. The Delta Lake transaction log guarantees exactly-once processing, even when there are other streams or batch queries running concurrently against the table. By default, streams run in append mode, which adds new records to the table. Databricks provides quickstart documentation that explains the whole process.

At this point you've coded up a script or written a program to get the data you want and successfully moved it into your data warehouse. But how will you load new or updated data? It's not a good idea to replicate all of your data each time you have updated records. That process would be painfully slow and resource-intensive.

Instead, identify key fields that your script can use to bookmark its progression through the data and use to pick up where it left off as it looks for updated data. Auto-incrementing fields such as updated_at or created_at work best for this. When you've built in this functionality, you can set up your script as a cron job or continuous loop to get new data as it appears in Recurly.

And remember, as with any code, once you write it, you have to maintain it. If Recurly modifies its API, or the API sends a field with a datatype your code doesn't recognize, you may have to modify the script. If your users want slightly different information, you definitely will have to.

Delta Lake on Databricks is great, but sometimes you need to optimize for different things when you're choosing a data warehouse. Some folks choose to go with Amazon Redshift, Google BigQuery, PostgreSQL, or Snowflake, which are RDBMSes that use similar SQL syntax, or Panoply, which works with Redshift instances. Others choose a data lake, like Amazon S3. If you're interested in seeing the relevant steps for loading data into one of these platforms, check out To Redshift, To BigQuery, To Postgres, To Snowflake, To Panoply, and To S3.