wehub-resource-sync
e071084ebe
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73 lines
2.5 KiB
Markdown
73 lines
2.5 KiB
Markdown
# Durable Flow
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A workflow that survives a crash and resumes where it stopped.
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A `flow` can be an ordered list of **steps** — a task with stages —
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instead of a single LLM turn. Each step is checkpointed before and after
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through a pluggable `Checkpoint` (store-backed by default), so if the
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process dies mid-run, the run resumes at the step it stopped on, without
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re-running the steps that already completed (and already had their side
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effects).
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## What this shows
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A three-step checkout (`reserve → charge → confirm`) whose `charge` step
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fails the first time, simulating a transient outage / crash:
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```
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first run:
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reserve → inventory reserved
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charge → payment dependency unavailable (crash)
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run failed: payment gateway timeout
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checkpoint: run 70643f61 is at step "charge" (status failed)
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resume:
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charge → payment captured
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confirm → order confirmed
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reserve ran 1 time(s) total — completed steps are not repeated on resume
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no pending runs — the workflow completed durably
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```
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The key line is the last pair: on `Resume`, `reserve` does **not** run
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again — its result was checkpointed — and the run finishes.
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## The pieces
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```go
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f := micro.NewFlow("checkout",
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micro.FlowSteps(
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micro.FlowStep{Name: "reserve", Run: reserve},
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micro.FlowStep{Name: "charge", Run: charge},
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micro.FlowStep{Name: "confirm", Run: confirm},
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),
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micro.FlowWithCheckpoint(micro.StoreCheckpoint(nil, "checkout")), // nil store = default; "checkout" = key scope
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)
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f.Execute(ctx, `{}`) // runs; crashes at charge
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pending, _ := f.Pending(ctx) // the run, checkpointed at "charge"
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f.Resume(ctx, pending[0].ID) // continues from charge to the end
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```
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- **`State`** carries a typed payload (`Set`/`Scan`) plus a `Stage`
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marker — the resume point.
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- **`Checkpoint`** persists each `Run`. The built-in is store-backed and
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keeps each flow's runs in their own store table (database `flow`, table
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`checkout`) via `store.Scope`, so one flow's runs don't share a table
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with another's — or with agent or service state. Point the default
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store at Postgres or NATS KV and a run survives a real process restart,
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or implement the interface to plug in Temporal, Restate, etc.
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- A real step would be `flow.Call(service, endpoint)` (an RPC),
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`flow.Dispatch(agent)` (hand off to an agent), or `flow.LLM(prompt)`
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(one model turn). Here they're plain funcs so durability is the only
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thing on display.
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## Run
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```bash
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go run main.go
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```
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No LLM key required.
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