A2a Dev Patterns

A2A Development Patterns

Before writing code

Fetch live docs:

1. Fetch https://a2a-protocol.org/latest/specification/ for the latest protocol details
2. Web-search a2a protocol best practices multi-agent architecture for community patterns
3. Web-search site:github.com a2aproject A2A samples patterns for reference architectures
4. Web-search multi-agent system design patterns for general multi-agent architecture guidance

Conceptual Architecture

Orchestration Topologies

Hub-and-Spoke (Orchestrator)

A central coordinator agent delegates subtasks to specialist agents:

                    ┌→ Research Agent
Coordinator Agent ──┼→ Analysis Agent
                    └→ Writing Agent

• Pros: Centralized control, clear task routing, easy to monitor
• Cons: Single point of failure, coordinator bottleneck
• Use when: Well-defined subtask decomposition, need for aggregation

Peer-to-Peer (Mesh)

Agents discover and communicate directly with each other:

Agent A ←→ Agent B
  ↕           ↕
Agent C ←→ Agent D

• Pros: No single point of failure, flexible
• Cons: Complex routing, harder to monitor, potential loops
• Use when: Agents are loosely coupled, dynamic discovery needed

Pipeline (Chain)

Tasks flow through a sequence of agents:

Input → Agent A → Agent B → Agent C → Output

• Pros: Simple flow, easy to reason about, composable
• Cons: Sequential latency, failure in one stage blocks all
• Use when: Clear transformation stages, ETL-like workflows

Hierarchical (Tree)

Manager agents delegate to team agents, which may further delegate:

CEO Agent
├── Marketing Manager Agent
│   ├── Content Agent
│   └── SEO Agent
└── Engineering Manager Agent
    ├── Frontend Agent
    └── Backend Agent

• Pros: Natural decomposition, scoped authority, scalable
• Cons: Deep hierarchies add latency, complex coordination
• Use when: Large organizations of agents, domain separation

Idempotency

Design A2A interactions to be idempotent:

• Use deterministic task IDs (hash of input + context) when possible
• Handle duplicate message/send requests gracefully
• Store task results for replay on retry
• Use request IDs for deduplication at the transport level

Observability

Multi-agent systems need deep observability:

Distributed tracing:

• Propagate trace IDs through A2A task metadata
• Log entry/exit for each agent in the chain
• Use OpenTelemetry or similar for cross-agent tracing

Metrics:

• Task latency per agent
• Task success/failure rates
• Message volume and throughput
• Active task count per agent
• Error code distribution

Logging:

• Log all JSON-RPC requests/responses (with sensitive data redacted)
• Include task IDs and request IDs in all log entries
• Log state transitions with timestamps

Agent Registries

For systems with many agents:

• Centralized registry — Agents register their Agent Cards; clients query by skill/tag
• DNS-based discovery — Agent Cards at well-known URLs
• Service mesh — Use infrastructure-level service discovery

Versioning

A2A agents evolve over time:

• Agent Card version — Update when skills or capabilities change
• Skill versioning — Individual skills can be versioned
• Protocol version — Track which A2A spec version you implement
• Breaking changes — Update the Agent Card URL or version for breaking changes
• Backward compatibility — Support old and new message formats during transitions

Security Patterns

• Zero trust — Authenticate every agent-to-agent call
• Least privilege — Agents only get access to the skills they need
• Audit trail — Log all cross-agent interactions for compliance
• Secret management — Use vaults for API keys and credentials, never hardcode

Production Deployment

• Health checks — Implement /health endpoints alongside the A2A endpoint
• Graceful shutdown — Complete or cancel in-flight tasks before stopping
• Scaling — A2A servers are stateless per-request; task store handles state
• Load balancing — Standard HTTP load balancing works for A2A endpoints
• Rate limiting — Protect agents from being overwhelmed by requests
• Circuit breakers — Stop calling failing agents, use fallbacks

Error Recovery Patterns

• Retry with backoff — Transient failures, exponential backoff
• Fallback agents — If primary agent fails, try an alternative
• Dead letter queue — Store failed tasks for later analysis/replay
• Compensation — If a multi-step workflow fails midway, undo completed steps
• Timeout escalation — If a task is stuck, escalate to a human or different agent

Best Practices

• Start simple — hub-and-spoke before mesh
• Design for failure — every agent call can fail
• Make agents stateless where possible — state lives in the task store
• Use structured DataParts for inter-agent data, not serialized text
• Monitor everything — you can't debug what you can't see
• Version your Agent Cards and document changes
• Test the full topology, not just individual agents
• Set SLOs for agent response times and success rates

Fetch the latest A2A specification and community patterns before implementing multi-agent architectures.