adrielc/helios-alpha/golem-configure-durability-rust

Configuring Agent Durability (Rust)

Durable Agents (Default)

By default, all Golem agents are durable:

• State persists across invocations, failures, and restarts
• Every side effect is recorded in an oplog (operation log)
• On failure, the agent is transparently recovered by replaying the oplog
• No special code needed — durability is automatic

You cannot opt out of oplog writes for a durable agent. The oplog is how durability works — every side effect must be recorded. If you are worried about oplog volume or replay cost (long-running agents, heartbeats, polling, recurring tasks), do not try to skip persistence. Use durable with periodic snapshots instead (see below).

A standard durable agent:

use golem_rust::{agent_definition, agent_implementation};
 
#[agent_definition]
pub trait CounterAgent {
    fn new(name: String) -> Self;
    fn increment(&mut self) -> u32;
    fn get_count(&self) -> u32;
}
 
struct CounterAgentImpl {
    name: String,
    count: u32,
}
 
#[agent_implementation]
impl CounterAgent for CounterAgentImpl {
    fn new(name: String) -> Self {
        Self { name, count: 0 }
    }
 
    fn increment(&mut self) -> u32 {
        self.count += 1;
        self.count
    }
 
    fn get_count(&self) -> u32 {
        self.count
    }
}

Durable with Periodic Snapshots

Same durability guarantees as the default durable mode, but recovery starts from the latest snapshot instead of replaying the full oplog from the beginning. Use this whenever the oplog grows unboundedly — long-running agents, high-frequency state changes, heartbeats, polling loops, recurring tasks.

#[agent_definition(snapshotting = "every(10)")]   // snapshot every 10 successful calls
pub trait CounterAgent { ... }
 
#[agent_definition(snapshotting = "periodic(30s)")]  // or at most once per interval
pub trait HeartbeatAgent { ... }

See `golem-custom-snapshot-rust` for snapshotting modes and serde-based or custom save_snapshot / load_snapshot implementations.

Ephemeral Agents

Use ephemeral mode for stateless, per-invocation agents where persistence is not needed:

• State is discarded after each invocation completes
• No oplog is maintained — lower overhead
• Useful for pure functions, request handlers, or adapters

#[agent_definition(ephemeral)]
pub trait StatelessHandler {
    fn new() -> Self;
    fn handle(&self, input: String) -> String;
}

When to Choose Which

When in doubt, use the default (durable). Ephemeral mode is an optimization for agents that genuinely don't need persistence. Add periodic snapshots whenever recovery time matters — see `golem-custom-snapshot-rust`.