Multi-Agent Orchestration Using Step Functions on AWS
Over the last few posts, we laid the foundation for a scalable, multi-agent LLM system on AWS. If you've followed along, you're already familiar with how we receive, sanitize, and route messages to individual Lambda-powered agents.
But what happens when multiple agents need to collaborate? Or when routing logic depends on dynamic conditions?
That's where AWS Step Functions enters the picture — providing an elegant way to coordinate agent behavior, enforce routing logic, and manage execution flow across components.
From Agents to Orchestration: Connecting the Dots
This post focuses on how Step Functions orchestrates the workflow:
Routing messages based on the to_agent field Managing state/session across agents Integrating external tool servers (like the MCP server) Returning responses to the originating channel
We'll walk through just enough code to make this orchestration tangible — nothing more than what's needed to understand the flow.
Why Use Step Functions for Agent Orchestration?
When multiple agents are involved (AWS agent, Salesforce agent, Comms agent, etc.), hardcoding call flows becomes brittle fast. Instead, we need:
Conditional routing based on message metadata (to_agent, context, etc.) Retry logic, parallel execution, and future extensions like long-running workflows Isolation and modularity so each agent Lambda can scale independently
Enter AWS Step Functions — our choice for orchestrating dynamic agent workflows.
How Step Functions Enable Dynamic Routing
The core of this design is the router Lambda, which reads incoming messages from the unified SQS channel and kicks off a Step Function. This Step Function then:
Reads metadata (to_agent, session_id, etc.) Invokes the appropriate agent Lambda Updates session state in DynamoDB Returns a response or invokes follow-up agents if needed
Each agent is fully stateless, pulling its session context on demand — making the system horizontally scalable.
Core Idea
Each agent is a standalone Lambda function that:
Receives input Performs a task Returns a new message and the name of the nextagent
The Step Function does the rest:
Checks if nextagent == "END" → finishes the flow. Looks up the agent's Lambda ARN from DynamoDB. Invokes the Lambda using waitForTaskToken. Unpacks the result and loops.
Why This Pattern Works
No hardcoding agent flow No redeploying Step Function for flow changes Pluggable architecture – agents can be developed independently Full audit and observability via Step Functions
You can plug in agents for summarization, translation, filtering, routing — even logic-driven multi-agent negotiation — all without touching your orchestration logic.
Source Code
You can find the full working setup (SAM templates, Step Function definition, Lambda code, and infra setup) here: