A2A – agentgateway | Agent Connectivity Solved

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A2A

Proxy requests to an agent that communicates via the agent-to-agent protocol (A2A).

About A2A

Agent-to-agent, or A2A, is an open protocol that enables communication and interoperability between opaque agentic applications. Developed by Google, A2A defines a common language that enables agents to show their capabilities and help them negotiate how they interact with the user, such as via text, forms, or bidirectional audio or video, irrespective of the framework or vendor they are built on.

Set up the agentgateway

Create an agentgateway that proxies requests to the reimbursement agent that you created earlier.

Create a listener and target configuration for your agentgateway. In this example, the agentgateway is configured as follows:
- Listener: An HTTP listener is configured for the A2A protocol and exposed on port 3000.
- Backend: The agentgateway targets a backend on your localhost port 9999, which you create in a subsequent step.
```
cat <<EOF > config.yaml
binds:
   - port: 3000
     listeners:
     - routes:
       - policies:
           # Mark this route as a2a traffic
           a2a: {}
         backends:
         - host: localhost:9999
EOF
```
Create the agentgateway.
```
agentgateway -f config.yaml
```

Set up an ADK agent

The following steps use the A2A sample repository.

Clone the A2A sample repository.

git clone https://github.com/a2aproject/a2a-samples.git

Navigate to the samples/python directory.
```
cd a2a-samples/samples/python
```
Run the Hello World agent.
```
uv run agents/helloworld
```

Verify the A2A connection

In another terminal tab but still from the python samples directory, install the dependencies for the Hello World agent.
```
uv pip install .
```

Run the client and send several test messages to the Hello World agent.

uv run hosts/cli --agent http://localhost:3000

Example output:

======= Agent Card ========
{"capabilities":{"streaming":true},"defaultInputModes":["text"],"defaultOutputModes":["text"],"description":"Just a hello world agent","name":"Hello World Agent","protocolVersion":"0.2.5","skills":[{"description":"just returns hello world","examples":["hi","hello world"],"id":"hello_world","name":"Returns hello world","tags":["hello world"]}],"supportsAuthenticatedExtendedCard":true,"url":"http://localhost:3000","version":"1.0.0"}
=========  starting a new task ======== 

What do you want to send to the agent? (:q or quit to exit):

Type a sample message, such as hi, and then send the message by pressing enter.

In another terminal tab, manually send a request to the agent card endpoint through agentgateway.

curl localhost:3000/.well-known/agent.json | jq

Example output: Notice that the url field is rewritten to point to the agentgateway.

{
  "capabilities": {
    "streaming": true
  },
  "defaultInputModes": [
    "text"
  ],
  "defaultOutputModes": [
    "text"
  ],
  "description": "Just a hello world agent",
  "name": "Hello World Agent",
  "protocolVersion": "0.2.5",
  "skills": [
    {
      "description": "just returns hello world",
      "examples": [
        "hi",
        "hello world"
      ],
      "id": "hello_world",
      "name": "Returns hello world",
      "tags": [
        "hello world"
      ]
    }
  ],
  "supportsAuthenticatedExtendedCard": true,
  "url": "http://localhost:3000",
  "version": "1.0.0"
}

In the tab where the agentgateway is running, verify that you see request logs from your client query to the Hello World agent, such as the following example.

2025-07-10T18:10:46.547567Z	info	request	gateway=bind/3000 listener=listener0 route=route0 endpoint=localhost:9999 src.addr=[::1]:59257 http.method=POST http.host=localhost http.path=/ http.version=HTTP/1.1 http.status=200 a2a.method=message/stream duration=3ms

Set up backends MCP