Continuous Workflows

In some use cases, you may need a workflow that executes forever or runs for a long duration, for example, a workflow that monitors the health of a server fleet. Since Amazon SWF keeps the entire history of a workflow execution, the history will keep growing over time. The framework retrieves this history from Amazon SWF when it performs a replay and this will become expensive if the history size is too large. In such long running or continuous workflows, you should periodically close the current execution and start a new one to continue processing. This is a logical continuation of the workflow execution. The generated self client can be used for this purpose. In your workflow implementation, simply call the @Execute method on the self client. Once the current execution completes, the framework will start a new execution using the same workflow Id.

You can also continue the execution by calling the continueAsNewOnCompletion method on the GenericWorkflowClient that you can retrieve from the current DecisionContext. For example, the following workflow implementation sets a timer to fire after a day and calls its own entry point to start a new execution.

public class ContinueAsNewWorkflowImpl implements ContinueAsNewWorkflow {
    
    private DecisionContextProvider contextProvider 
         = new DecisionContextProviderImpl();
    
    private ContinueAsNewWorkflowSelfClient selfClient 
         = new ContinueAsNewWorkflowSelfClientImpl();  

    private WorkflowClock clock 
         = contextProvider.getDecisionContext().getWorkflowClock();
    
    @Override
    public void startWorkflow() {
        Promise<Void> timer = clock.createTimer(86400);
        continueAsNew(timer);
    }
    
    @Asynchronous
    void continueAsNew(Promise<Void> timer) {
        selfClient.startWorkflow();
    }
}

When a workflow recursively calls itself, the framework will close the current workflow when all pending tasks have completed and start a new workflow execution. Note that as long as there are pending tasks, the current workflow execution will not close. The new execution will not automatically inherit any history or data from the original execution; if you want to carry over some state to the new execution, then you must pass it explicitly as input.