Day 33: Agents on Step Functions, Not Infinite Loops

A while loop in Lambda that calls Bedrock until “done” is a token incinerator without audit. Step Functions give you timeouts, maps, human approval via task tokens, and compensations finance will accept. Day 33 replaces infinite ReAct with an explicit graph.

⚡ TL;DR: Model turns as states: plan → toolChoice → tool/approve → evaluate → succeed|compensate. Cap iterations and token budget in state. Use Standard workflows for human-in-the-loop, Express for short chats.

Graph beats soup

Start → Plan → ToolChoice →
  Choice:
    needs_approval → WaitForTaskToken
    safe_tool → InvokeTool → Evaluate →
      (continue | succeed | fail_compensate)

for i in range(100):
    out = converse(...)
    if not out.tool_calls: break
    run_tools(out.tool_calls)

Human approval with task tokens

{
  "Type": "Task",
  "Resource": "arn:aws:states:::lambda:invoke.waitForTaskToken",
  "Parameters": {
    "FunctionName": "requestApproval",
    "Payload": {
      "taskToken.$": "$$.Task.Token",
      "diff.$": "$.proposedPatch",
      "sessionId.$": "$.sessionId"
    }
  },
  "TimeoutSeconds": 86400,
  "HeartbeatSeconds": 3600
}

Approval posts to Slack/Jira; Approve calls SendTaskSuccess. Heartbeats detect abandoned approvals.

Compensations and budgets

If create_resources succeeds and register_dns fails, a compensating state deletes resources. Track tokens_used and iteration in state; fail closed when budgets exceed — do not rely on the model to stop.

Production checklist

• [ ] Max iteration + token budget in state
• [ ] waitForTaskToken for mutating actions
• [ ] Compensating transitions on failure paths
• [ ] Execution history retained for replay
• [ ] Alarms on failure rate and stuck approvals
• [ ] Game-day: force compensate path once per quarter

Series navigation

← Day 32 · Day 34 →

Last updated September 11, 2026