Inter-Process Communication (IPC)

Pando’s IPC system enables multiple instances to communicate, share state, and coordinate work across a single machine. Built on ZeroMQ, it provides pub/sub event broadcasting and JSON-RPC 2.0 request/response messaging.

Architecture

• Primary instance: Creates the IPC bus with PUB (events) and ROUTER (RPC) sockets
• Secondary instances: Connect via SUB (events) and DEALER (RPC)
• Instance registry: File-based tracking at /tmp/pando-instances/

Features

Session Synchronization

Secondary instances receive real-time session updates from the primary:

• Session creation, activation, deletion
• Message append events
• LLM streaming tokens (start, token, end)
• Tool execution events (start, end)

Primary/Secondary Failover

A watcher monitors primary liveness via heartbeats. When the primary dies:

1. A secondary detects the missing heartbeat
2. Acquires an exclusive file lock
3. Promotes itself to primary
4. Publishes instance.promoted so other secondaries reconnect

Write Coordination

Only the primary instance performs database writes. Secondaries route write requests (like db.compact) to the primary over IPC.

Hot-Peer Delegation

Instances can delegate tasks to external peer instances:

[Mesnada.Delegation]
AllowExternalWarmTargets = true   # caller-side opt-in
AcceptDelegations = true           # target-side opt-in

RPC Methods

Configuration

IPC is configured automatically when multiple instances are running. Failover settings:

# Automatic configuration via internal defaults:
# HeartbeatInterval: 5s
# HeartbeatTimeout: 15s
# ProbeInterval: 60s
# Enabled: true