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Load Testing Agent-to-Agent (A2A) API Calls

What is the A2A Protocol?​

The Agent-to-Agent (A2A) protocol is an open protocol that enables communication and interoperability between opaque agentic applications. As AI systems become more specialized and distributed, A2A provides a standardized way for diverse AI agents built on different frameworks and hosted on separate servers to discover, negotiate with, and collaborate on tasks.

Key Features of A2A​

The A2A protocol solves the challenge of agent silos by enabling:

  • Discovery: Agents expose their capabilities through "Agent Cards" that detail what they can do and how to connect
  • Negotiation: Agents can negotiate preferred interaction formats including text, forms, and media
  • Collaboration: Multiple agents can work together securely on extended tasks
  • Opacity: Agents collaborate without revealing internal state, memory, or proprietary tools

Technical Foundation​

The A2A protocol is built on standard web technologies:

  • Protocol: JSON-RPC 2.0 over HTTP(S) for standardized messaging
  • Communication Patterns:
    • Synchronous request/response exchanges
    • Streaming via Server-Sent Events (SSE)
    • Asynchronous push notifications
  • Data Types: Text, files, and structured JSON payloads

The A2A Protocol is a Linux Foundation open-source project with contributions from Google, licensed under Apache 2.0.

Load Testing A2A with Speedscale​

Since A2A uses JSON-RPC 2.0 over HTTP(S), it can be load tested like any other HTTP-based API using Speedscale's traffic replay capabilities. The standard HTTP foundation means existing load testing infrastructure and techniques apply directly to A2A implementations.

How Traffic Replay Works for A2A​

Speedscale captures real A2A traffic between agents and replays it at scale:

  1. Capture: Deploy the Speedscale sidecar to capture live A2A traffic between your agents, including JSON-RPC calls, SSE streams, and async notifications
  2. Transform: Use extractors and transformers to handle dynamic values in Agent Cards, session tokens, or agent-specific identifiers
  3. Replay: Configure a test config with your desired load pattern (see Load Testing guide)
  4. Analyze: Review response accuracy, latency, and throughput to identify bottlenecks

Configuring Load Patterns for A2A​

A2A workloads often involve complex multi-agent interactions. Consider these approaches:

  • Staged Load: Gradually increase RPS to simulate agent network growth
  • Soak Testing: Run sustained load to expose resource leaks in long-running agent conversations
  • Low Data Mode: Enable low data mode for high-throughput testing while focusing on status codes and errors

See the Load Testing guide for detailed configuration instructions.

Common Performance and Testing Issues with A2A​

1. Long-Running Agent Conversations​

A2A enables extended multi-turn conversations between agents. These long-lived sessions can:

  • Exhaust connection pools if not properly managed
  • Cause memory leaks in state management
  • Create cascading delays when agents wait on each other

Testing Strategy: Use soak tests with realistic conversation lengths to identify memory leaks and connection exhaustion. Monitor agent response times throughout the test duration.

2. Server-Sent Events (SSE) Streaming​

A2A's streaming support via SSE introduces specific challenges:

  • Connection timeout configuration must accommodate streaming duration
  • Load balancers may drop long-lived connections
  • High connection counts from streaming can saturate file descriptors

Testing Strategy: Capture and replay SSE streams to validate connection stability. Test with various load balancer timeout configurations to ensure streaming reliability at scale.

3. Agent Discovery and Negotiation Overhead​

The A2A discovery phase involves:

  • Fetching and parsing Agent Cards
  • Content negotiation between agents
  • Capability matching and format selection

Testing Strategy: Measure the time agents spend in discovery vs. actual work. Consider caching Agent Cards when appropriate to reduce discovery overhead.

4. JSON-RPC Error Handling​

JSON-RPC 2.0 defines specific error codes and structures. Common issues include:

  • Improper error propagation between agents
  • Timeout handling when dependent agents become unresponsive
  • Inconsistent error response formats

Testing Strategy: Use assertions to validate JSON-RPC error responses. Test failure scenarios where downstream agents return errors or time out.

5. Dynamic Agent Networks​

In production A2A deployments, agent availability changes dynamically:

  • Agents may come online or go offline
  • Agent capabilities may be updated
  • Network topology changes as agents are added

Testing Strategy: Capture traffic from various network states. Test with different agent configurations to ensure your system handles topology changes gracefully.

6. Authentication and Security​

A2A communications often involve:

  • Agent authentication and authorization
  • Secure token exchange between agents
  • Rate limiting and abuse prevention

Testing Strategy: Use Speedscale's transform capabilities to handle authentication tokens during replay. Test rate limiting behavior under high load to ensure legitimate agent traffic isn't blocked.

Best Practices​

  1. Capture Representative Traffic: Ensure your captured snapshots include the full range of A2A interactions: discovery, negotiation, synchronous calls, and streaming
  2. Test Agent Independence: Load test individual agents as well as the full agent network to identify single points of failure
  3. Monitor End-to-End Latency: Track total conversation time across multiple agent hops, not just individual request latency
  4. Validate Agent Card Changes: Test backward compatibility when updating agent capabilities to ensure existing agent relationships continue working

Learn More​