Draft: Start Workflow Execution

Objective

Start a (minimalist) workflow execution (and for that end shape the structure of the gRPC service)

Related issues

• #14
• #12

Highlights

• gRPC contract updates
• Controllers
• Workflow Execution Loop

gRPC contract updates

• ExecuteWorkflow is a bidirectional streaming RPC that allows the DuoWorkflowExecutor to send a ExecuteWorkflowRequest message and receive ExecuteWorkflowResponse messages.

• ExecuteWorkflowRequest — Requests DuoWorkflowExecutor may send to the DuoWorkflowService

  • StartWorkflow — Create and start a new workflow
  • CommandResult — Send results of a command execution to the DuoWorkflowService
  • RestartWorkflow — Restarts a workflow execution optionally from Checkpoint ID

• ExecuteWorkflowResponse — Responses DuoWorkflowService may send to the DuoWorkflowExecutor

  • ExecuteCommand — Instruct DuoWorkflowExecutor to execute a script or binary
  • HttpRequestCommand — Instruct DuoWorkflowExecutor to make an HTTP request
  • ReadFileCommand — Instruct DuoWorkflowExecutor to read a file
  • WriteFileCommand — Instruct DuoWorkflowExecutor to write a file
  • WorkflowCreated — Notify DuoWorkflowExecutor that a new workflow has been created
  • WorkflowCheckpointed — Notify DuoWorkflowExecutor that a workflow has been checkpointed
  • WorkflowCompleted — Notify DuoWorkflowExecutor that a workflow has been completed

Controllers

• gRPC service has only one long-running, bi-directional endpoint
• "Routing" is done based on requests to this endpoint
• We use "Controllers" as a pattern to distribute implementation while maintaining familiarity humans working on this code-base
• To be implemented in this MR:
  • StartWorkflow
• To be scaffolded in this MR
  • CommandResult
  • RestartWorkflow

Workflow execution loop

• Logic for centralised execution loop for each workflow
• Triggered by all/most controllers