Building Collaborative Microservices in Python with FastAPI: Echo & Reverse Agents (Beginner -Part1)

[[{“value”:”

Microservices encourage us to build distributed systems consisting of small, specialized components that communicate seamlessly. In this post, let’s explore a simple yet illustrative example: Agent-A and Agent-B, two FastAPI-based Python microservices that interact in real-time.

We’ll see how Agent-A receives a request, calls Agent-B, and returns a transformed response—demonstrating the foundations of service-to-service HTTP communication.

The Objective

We want to create:

• Agent-B: A service that reverses text.
• Agent-A: A service that takes a string, sends it to Agent-B for reversal, and returns the reversed string as a response.

Both services are built with FastAPI and use Pydantic for data validation.

Meet Agent-B: The Reverse Service

Let’s begin by looking at agent_b.py. It’s a minimal service that exposes one endpoint that takes a string and returns it reversed.

from fastapi import FastAPI
from pydantic import BaseModel
import os

PORT = int(os.getenv(“AGENT_B_PORT”, 8001))
app = FastAPI(title=”Agent-B”)

class ReverseRequest(BaseModel):
text: str

class ReverseResponse(BaseModel):
source: str
reversed: str

@app.post(“/reverse”, response_model=ReverseResponse)
def reverse(req: ReverseRequest):
return ReverseResponse(source=”Agent-B”, reversed=req.text[::-1])

Meet Agent-A: The Forwarding Echo Service

Now, let’s look at agent_a.py. While it’s called an “echo” service, it doesn’t simply echo back input. Instead, it forwards the input to Agent-B, receives the reversed string, and returns that. This demonstrates microservice orchestration.

agent_a.py

from fastapi import FastAPI
from pydantic import BaseModel
import httpx
import os

PORT = int(os.getenv(“AGENT_A_PORT”, 8000))
B_URL = os.getenv(“AGENT_B_URL”, “http://localhost:8001”)
app = FastAPI(title=”Agent-A”)

class EchoRequest(BaseModel):
text: str

class EchoResponse(BaseModel):
source: str
echoed: str

@app.post(“/echo”, response_model=EchoResponse)
async def echo(req: EchoRequest):
# Forward the text to Agent-B
async with httpx.AsyncClient() as client:
r = await client.post(f”{B_URL}/reverse”, json={“text”: req.text})
r.raise_for_status()
reversed_text = r.json()[“reversed”]
# Respond with what Agent-B returned
return EchoResponse(source=”Agent-A”, echoed=reversed_text)

Running Both Agents

1. Start Agent-B:

   uvicorn agent_b:app --port 8001

2. Start Agent-A:

   uvicorn agent_a:app --port 8000

“}]] 

 [[{“value”:”Microservices encourage us to build distributed systems consisting of small, specialized components that communicate seamlessly. In this post, let’s explore a simple yet illustrative example: Agent-A and Agent-B, two FastAPI-based Python microservices that interact in real-time.We’ll see how Agent-A receives a request, calls Agent-B, and returns a transformed response—demonstrating the foundations of service-to-service HTTP communication.The ObjectiveWe want to create:Agent-B: A service that reverses text.Agent-A: A service that takes a string, sends it to Agent-B for reversal, and returns the reversed string as a response.Both services are built with FastAPI and use Pydantic for data validation.Meet Agent-B: The Reverse ServiceLet’s begin by looking at agent_b.py. It’s a minimal service that exposes one endpoint that takes a string and returns it reversed.from fastapi import FastAPI
from pydantic import BaseModel
import os

PORT = int(os.getenv(“AGENT_B_PORT”, 8001))
app = FastAPI(title=”Agent-B”)

class ReverseRequest(BaseModel):
text: str

class ReverseResponse(BaseModel):
source: str
reversed: str

@app.post(“/reverse”, response_model=ReverseResponse)
def reverse(req: ReverseRequest):
return ReverseResponse(source=”Agent-B”, reversed=req.text[::-1]) Meet Agent-A: The Forwarding Echo ServiceNow, let’s look at agent_a.py. While it’s called an “echo” service, it doesn’t simply echo back input. Instead, it forwards the input to Agent-B, receives the reversed string, and returns that. This demonstrates microservice orchestration.agent_a.pyfrom fastapi import FastAPI
from pydantic import BaseModel
import httpx
import os

PORT = int(os.getenv(“AGENT_A_PORT”, 8000))
B_URL = os.getenv(“AGENT_B_URL”, “http://localhost:8001”)
app = FastAPI(title=”Agent-A”)

class EchoRequest(BaseModel):
text: str

class EchoResponse(BaseModel):
source: str
echoed: str

@app.post(“/echo”, response_model=EchoResponse)
async def echo(req: EchoRequest):
# Forward the text to Agent-B
async with httpx.AsyncClient() as client:
r = await client.post(f”{B_URL}/reverse”, json={“text”: req.text})
r.raise_for_status()
reversed_text = r.json()[“reversed”]
# Respond with what Agent-B returned
return EchoResponse(source=”Agent-A”, echoed=reversed_text)Running Both AgentsStart Agent-B:uvicorn agent_b:app –port 8001Start Agent-A:uvicorn agent_a:app –port 8000″}]] Read More Technology Blog Posts by SAP articles 

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