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application-design-and-implementation.md

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application-design
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How to design and implement the Background Check application
Start by mapping business process to Workflows.
Go
SDK
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What business processes are map to Workflows?

The application maps each of the following business processes to its own Workflow Definition:

Why use Child Workflows for Searches instead of Activities?

This application uses Child Workflows for Searches for a few reasons.

  1. Each Search could be long running: In a real-life scenario, you won't know how long a Search might take to return a result. Individual Searches and Background Checks overall can often take hours or days to complete. Although Temporal supports long running Activities, an actual Search is conducted by a third-party system, so Heartbeats are not very helpful here. An Activity does make the call to the third-party system, but you can set a Timeout on the Activity Execution and let the Workflow Execution be the long running process.
  2. Division of responsibilities: In a real-life scenario, you might have a team that is dedicated to a particular Search. The Background Check team manages their Workflow Definition, while the Federal Criminal Search team manages its own Workflow Definition, for example, to create a sort of inter-team distributed system that can work together to accomplish goals. This makes it easier when it comes to delegating responsibilities around bug fixes and CI/CD pipelines.
  3. The state of a Workflow is maintained: The results of an Activity are written to the Workflow Execution Event History. Instead of writing Search results directly to the Background Check Workflow Execution, keep them separate in their own Workflow Execution and access them independently from the Background Check Workflow.
  4. Reduces the need to version the main Background Check Workflow: Workflow Execution Event Histories are separated.

Which steps within a business process map to Activities?

This application uses Activities for the following business sub-processes:

  • Sending email
  • Calling third-party APIs

Sending an email message and calling third party APIs are considered unreliable steps in the business process.

What happens if an Activity Execution fails?

Activities are meant to handle the unreliable steps of the business process. To simulate unreliability, the sample adds middleware that produces about a 40% rate of failure on the third party API calls. This sample configures similar functionality with the Mailhog instance that causes random SMTP failures.

Activities each use a default Retry Policy. So when an Activity Task Execution fails the Temporal Cluster will try to execute the code again. The sample sets a Schedule-To-Close Timeout of 1 minute for each Activity Execution that limits that overall execution time. You won't ever wait longer than 1 minute for any given Activity Execution to complete. Using a Schedule-To-Close Timeout to limit the overall execution time is often a better solution that using the Maximum Attempts setting on the Retry Policy, as it provides a clear time cutoff for real life use cases.

If an Activity Execution does fail, it returns the error from the latest attempt to the Workflow Execution that spawned it. The Workflow then decides how to handle the fact that the Activity Execution failed.

What happens if an individual Search fails?

For demonstration purposes, if an Activity Execution does fail, the Workflow Execution (Or Child Workflow Execution) that spawned it returns the error that was returned from the Activity Execution, and the Workflow Execution closes with a Failed status

Should an individual Search fail, the Background Check still returns as much of the report as it can. The error that caused a Search to fail is included in the report. The one exception to this is if the SSN Trace Child Workflow Execution fails, as the addresses that are returned from that Search are required to conduct the remaining Searches.

If an individual Search fails, then the Company HR Person can choose to run another Background Check if they want.

Do you need a database?

No, you will not need a database for this application. All of the application state is maintained by the Temporal Cluster.

While a Workflow Execution is Running, its Event History (state) is perpetually maintained. When a Workflow Execution reaches a Closed status, the Temporal Cluster persists its Event History per the retention period.

In a real-life scenario, to persist the Event History of the Background Check longer than the Temporal Cluster retention period, you would have an additional business process Workflow to store Background Checks in a database, and an additional business process Workflow to retrieve them. Because the default retention period for a Temporal Cluster is 7 days, this application will not support that.

What does the component topology look like?

Diagram of component topology of the Temporal Application

The Temporal Client communicates with the Temporal Cluster (Temporal Server + Database).

The Temporal Cluster communicates with the Workers that execute the application code. The application has one Worker Process and one Worker Entity.

However, in real life,the application could use as many Worker Processes (each with multiple Worker Entities) as needed.

How do you ensure PII is encrypted in the Temporal Platform?

To ensure data is encrypted while in the Temporal Platform, you use a customized Data Converter.

How do you know what the status of a Background Check is

The status refers to the whether a Background Check is Open or Closed.

You can use the Temporal Platform's Visibility APIs to see the status of any oftheWorkflow Executions. In this application you wrapped the bgc-company list command around these Visibility APIs. You also make sure to add custom Search Attributes totheBackground Check Workflows. When you run bgc-company list you are using the Visibility APIs and passing a List Filter that gives us back only the Background Check Workflow Executions.

How do you know what the state of a Background Check is?

Not the same as "status", state refers to the values of variables in the Background Check Workflow Execution. You can know the state by sending a Query to a Background Check. The Background Check is developed to listen for a Query and provide data in response. The Background Check actually provides the same object in response to a Query as it does when the function returns. Temporal automatically provides the result of the function if the Workflow Execution is in a closed state when the Query is processed by the Temporal Cluster.

This means that you can use a Query to get the state of a Background Check at any time. You can see this implemented in the Background Check Workflow Definition where the Query Handler is set.

You also use a Query to get the details of the Candidate from the Employer Verification Workflow Execution when the Researcher uses the Web UI to load and verify the Candidate information.

How do you get data into a running Workflow Execution?

You use Signals to get data into a running Workflow Execution.

How do you handle a Cancellation Request of a business process?

Within a Workflow Definition, you have logic to explicitly handle a Cancellation Request, so you can "clean up" anything you need to prior to cancelling.