docs: durable & async Fission RFC series (statestore, async invocation, workflows)

config.toml

@@ -183,12 +183,21 @@ github = 'fission'
 slackurl = "/slack"
 twitter = 'fissionio'
 
+[[params.whatsnew]]
+badge = 'NEW'
+body = 'Durable & async Fission: a statestore substrate, fire-and-forget asynchronous invocation with retries and a dead-letter queue, and durable workflows that orchestrate functions as a resumable state machine.'
+heading = 'Durable & Async Workflows'
+[params.whatsnew.button]
+hero_class = 'mid'
+text = 'Explore Workflows'
+url = '/docs/usage/workflows/'
+
 [[params.whatsnew]]
 badge = 'RELEASE'
 body = 'Fission v1.27.0 is out! Zero-restart multi-namespace tenancy with per-namespace isolation, plus a developer toolkit — invocation correlation and failure attribution, fission function describe, and local development with run-local.'
 heading = 'Announcing Fission v1.27.0'
 [params.whatsnew.button]
-hero_class = 'mid'
+hero_class = 'mid-2'
 text = 'Read Release Notes'
 url = '/docs/releases/v1.27.0/'
 

content/en/_index.html

@@ -338,19 +338,18 @@ <h2 class="section-title">What's New</h2>
       </div>
       <div class="col-lg-4">
         <div class="card-shadow">
-          <span class="card-badge">RELEASE</span>
+          <span class="card-badge">NEW</span>
           <h4 class="section-text-bold mt-4">
-            Announcing Fission <span class="d-lg-block">v1.27.0</span>
+            Durable &amp; Async <span class="d-lg-block">Workflows</span>
           </h4>
           <div class="card-shadow-content">
             <p class="section-text">
-              Fission v1.27.0 is out! Zero-restart multi-namespace tenancy with
-              per-namespace isolation, invocation correlation and failure
-              attribution, fission function describe, and local development with
-              run-local.
+              A statestore substrate, fire-and-forget asynchronous invocation
+              with retries and a dead-letter queue, and durable workflows that
+              orchestrate functions as a resumable state machine.
             </p>
-            <a href="/docs/releases/v1.27.0/"
-              ><button class="hero-mid align-self-end">Release Notes</button></a
+            <a href="/docs/usage/workflows/"
+              ><button class="hero-mid align-self-end">Explore Workflows</button></a
             >
           </div>
         </div>

content/en/docs/architecture/_index.md

@@ -100,6 +100,9 @@ Invokes functions on a cron schedule.
 ### Canary Config
 Shifts traffic gradually between two function versions and rolls back automatically on failures.
 
+### [Statestore]({{% ref "statestore.md" %}})
+A durable state substrate (key/value, event log, queue) that backs durable workflows, asynchronous invocation, and eventing.
+
 ## Deprecated components
 
 ### [Controller]({{% ref "controller.md" %}})

content/en/docs/architecture/statestore.md

@@ -0,0 +1,107 @@
+---
+title: "Statestore"
+weight: 16
+description: >
+  A durable state substrate — key/value, an append-only event log, and a visibility-timeout queue — behind one interface with pluggable drivers.
+---
+
+**The statestore is the durable substrate the control plane writes to when a feature needs state that outlives a single request or a single pod.**
+
+It exposes three capabilities behind one interface — a **key/value** store, an append-only **event log**, and a visibility-timeout **queue** — served by a pluggable driver.
+Fission itself never deploys a database product: you either use the bundled embedded driver for development, or point the external driver at a database you already run.
+
+The statestore is what makes Fission's newer durable features possible.
+Starting with Fission {{< release-version >}}, three subsystems build on it:
+
+- **[Durable Workflows]({{% ref "/docs/usage/workflows/_index.md" %}})** record every step of a run in the event log, so a run survives a controller restart and resumes exactly where it stopped.
+- **[Asynchronous invocation]({{% ref "/docs/usage/function/async-invocation.md" %}})** enqueues each fire-and-forget call on the queue and delivers it in the background with retries and a dead-letter queue.
+- **Eventing** uses the event log and queue as its zero-broker transport.
+
+The statestore is off by default; a feature that needs it will tell you to enable it.
+
+```mermaid
+flowchart TB
+  wf["Workflow Engine"]:::fission
+  async["Async Router / Worker"]:::fission
+  evt["Eventing"]:::fission
+  subgraph ss["Statestore"]
+    kv["Key/Value"]:::store
+    log["Event Log (append-only, CAS)"]:::store
+    queue["Queue (visibility timeout)"]:::store
+  end
+  driver["Driver"]:::fission
+  embedded["SQLite on a PVC<br/>(embedded)"]:::pod
+  external["Postgres via DSN Secret<br/>(external)"]:::pod
+
+  wf --> log
+  async --> queue
+  evt --> log
+  evt --> queue
+  kv --> driver
+  log --> driver
+  queue --> driver
+  driver -->|"embedded"| embedded
+  driver -->|"external"| external
+
+  classDef fission fill:#e8f0fe,stroke:#2d70de,color:#1f2a43
+  classDef pod fill:#e6f7f1,stroke:#11a37f,color:#1f2a43,stroke-dasharray:5 3
+  classDef store fill:#fff7e0,stroke:#dba514,color:#1f2a43,stroke-dasharray:5 3
+```
+
+## Embedded vs external
+
+The driver is chosen with `statestore.mode`.
+The two modes differ only in where the state lives; the interface the features use is identical.
+
+| Mode | Driver | Where state lives | Use it for |
+| --- | --- | --- | --- |
+| `embedded` | SQLite | A bundled SQLite file on a `PersistentVolumeClaim` | Development, single-node, and evaluation. Simple to run; not highly available. |
+| `external` | Postgres | A database **you** run and manage | Production, high availability, and anything that needs KEDA autoscaling. |
+
+{{% notice warning %}}
+KEDA autoscaling for asynchronous invocation requires `statestore.mode=external`.
+The KEDA PostgreSQL scaler reads the backlog directly from the database and cannot reach the embedded SQLite file inside the pod.
+{{% /notice %}}
+
+## Enable the statestore
+
+The statestore is **off by default**.
+Enable it and pick a mode with Helm values.
+
+Embedded (SQLite on a PVC — development):
+
+```bash
+helm upgrade --install fission fission-charts/fission-all \
+  --namespace fission \
+  --set statestore.enabled=true \
+  --set statestore.mode=embedded \
+  --set statestore.embedded.size=1Gi
+```
+
+External (Postgres — production): create a Secret holding the DSN, then point the chart at it:
+
+```bash
+kubectl create secret generic statestore-postgres \
+  --namespace fission \
+  --from-literal=dsn='postgres://user:password@postgres.db.svc:5432/fission?sslmode=require'
+
+helm upgrade --install fission fission-charts/fission-all \
+  --namespace fission \
+  --set statestore.enabled=true \
+  --set statestore.mode=external
+```
+
+| Helm value | Default | Meaning |
+| --- | --- | --- |
+| `statestore.enabled` | `false` | Provision the statestore. Required by workflows, async invocation, and eventing. |
+| `statestore.mode` | `embedded` | `embedded` (SQLite on a PVC) or `external` (a Postgres DSN Secret). |
+| `statestore.embedded.size` | `1Gi` | Size of the PVC backing the embedded SQLite file. |
+| `statestore.external` | — | Name of the DSN Secret for external mode (defaults to `statestore-postgres`, key `dsn`). |
+
+Fission runs no database of its own in either mode: embedded is a file on a volume, and external is a database you already operate.
+
+## Related
+
+- [Durable Workflows]({{% ref "/docs/usage/workflows/_index.md" %}}) — multi-step orchestration recorded in the event log.
+- [Asynchronous Invocation]({{% ref "/docs/usage/function/async-invocation.md" %}}) — fire-and-forget calls delivered from the queue.
+- [Architecture overview]({{% ref "/docs/architecture/_index.md" %}}) — how the statestore sits alongside the other components.

content/en/docs/concepts/_index.md

@@ -59,6 +59,7 @@ Read the pages in order — they build on each other.
 - **[Executors]({{% ref "/docs/concepts/executors.md" %}})** — how Fission provisions and scales function pods (poolmgr vs newdeploy vs container).
 - **[Triggers]({{% ref "/docs/concepts/triggers.md" %}})** — the event sources that invoke your functions.
 - **[Packages and builds]({{% ref "/docs/concepts/packages-and-builds.md" %}})** — source and deployment archives, and the build pipeline.
+- **[Workflows]({{% ref "/docs/concepts/workflows.md" %}})** — orchestrate several functions as one durable, resumable state machine.
 - **[Comparison]({{% ref "/docs/concepts/comparison.md" %}})** — how Fission compares to Knative, OpenFaaS, Kubeless, and managed FaaS, and when to choose each.
 
 ## Specs: declarative configuration

content/en/docs/concepts/workflows.md

@@ -0,0 +1,77 @@
+---
+title: "Workflows"
+weight: 7
+description: >
+  A durable state machine over functions — a Workflow definition and its WorkflowRun executions, recorded step by step in the statestore so a run survives restarts and resumes where it stopped.
+---
+
+**A workflow is a durable state machine that orchestrates several functions as one reliable unit of work.**
+
+A single function is the right tool for one step.
+Real processes are usually several steps with logic between them — validate an order, screen it for fraud, charge the card, fulfill or reject — where some steps run in parallel, some are conditional, and some can fail transiently and must be retried.
+You *can* wire that together by having functions call each other, but then the orchestration lives in your code, nothing records how far a given execution got, and a crash midway leaves you guessing.
+A workflow makes the orchestration a first-class, durable object instead.
+
+## Definition and execution
+
+Workflows use two custom resources, mirroring the split between a program and a running process:
+
+- A **`Workflow`** is the *definition* — a named state machine that says which functions run, in what order, with what branching, retries, and error handling.
+- A **`WorkflowRun`** is one *execution* of that definition against a specific input. You create a run each time you want the workflow to happen; each run has its own state and history.
+
+The definition is authored once and reused; every invocation is a new run.
+
+## What makes it durable
+
+Every step a run takes — scheduled, succeeded, failed, retried, a timer fired, branches joined — is appended to an event log in the [statestore]({{% ref "/docs/architecture/statestore.md" %}}) using compare-and-swap, so the log is the single source of truth for where a run is.
+The engine's own state is derived: it rebuilds a run's position by folding its event log, then decides the next step.
+
+That design buys four things:
+
+- **Restart survival.** If the controller restarts mid-run, it reads the log back and continues — nothing is re-run that already succeeded, and nothing is lost.
+- **Resume exactly where it stopped.** A run picks up from its last recorded step, not from the beginning.
+- **Retries with backoff.** A transient function failure (a 5xx) is retried automatically; a permanent one (a 4xx typed error) is not.
+- **Typed-error routing.** A step can catch a named business error (`PaymentDeclined`) and route to a different state, separately from infrastructure retries.
+
+```mermaid
+flowchart TB
+  trigger["CLI / Trigger"]:::user -->|"create WorkflowRun"| engine["Workflow Engine"]:::fission
+  engine -->|"invoke step (internal path)"| router["Router"]:::fission
+  router --> pod["Function Pod"]:::pod
+  engine -->|"append every step (CAS)"| log["Statestore Event Log"]:::store
+  engine -->|"durable delay"| timers["wf-timers Queue"]:::store
+  log -.->|"fold to resume"| engine
+
+  classDef user fill:#ffffff,stroke:#94a3b8,color:#1f2a43
+  classDef fission fill:#e8f0fe,stroke:#2d70de,color:#1f2a43
+  classDef pod fill:#e6f7f1,stroke:#11a37f,color:#1f2a43,stroke-dasharray:5 3
+  classDef store fill:#fff7e0,stroke:#dba514,color:#1f2a43,stroke-dasharray:5 3
+```
+
+## The state types
+
+A workflow is built from a small set of state types:
+
+- **Task** — invoke a function.
+- **Choice** — branch on the data, with no function call.
+- **Parallel** — run several branches concurrently and join their results.
+- **Map** — run one branch per element of an array, with a concurrency limit.
+- **Wait** — pause the run durably for a set duration.
+- **Succeed** / **Fail** — terminate the run.
+
+See [Authoring workflows]({{% ref "/docs/usage/workflows/authoring.md" %}}) for the full field reference.
+
+## When to use a workflow
+
+Reach for a workflow when an operation is **multiple steps that must complete reliably as a whole** — especially with parallelism, conditional routing, retries, durable waits, or a need to know afterward exactly what happened.
+
+Prefer the simpler tools when they fit:
+
+- A single function, possibly async, is enough for one unit of work — see [Asynchronous invocation]({{% ref "/docs/usage/function/async-invocation.md" %}}).
+- Independent event-driven reactions are better modeled as separate [triggers]({{% ref "/docs/concepts/triggers.md" %}}).
+
+## Related
+
+- [Workflows usage guide]({{% ref "/docs/usage/workflows/_index.md" %}}) — enable, author, run, and inspect workflows.
+- [Statestore]({{% ref "/docs/architecture/statestore.md" %}}) — the durable event log a run is recorded in.
+- [Functions]({{% ref "/docs/concepts/functions.md" %}}) — the steps a workflow orchestrates.

content/en/docs/reference/fission-cli/fission.md

@@ -39,6 +39,8 @@ Fission: Fast and Simple Serverless Functions for Kubernetes
 * [fission tenant](/docs/reference/fission-cli/fission_tenant/)	 - Manage multi-namespace tenancy (onboard/offboard namespaces)
 * [fission timetrigger](/docs/reference/fission-cli/fission_timetrigger/)	 - Create, update and manage time triggers
 * [fission token](/docs/reference/fission-cli/fission_token/)	 - Create a JWT token for function invocation
+* [fission topic](/docs/reference/fission-cli/fission_topic/)	 - Publish to and inspect RFC-0027 eventing topics
 * [fission version](/docs/reference/fission-cli/fission_version/)	 - Show client/server version information
 * [fission watch](/docs/reference/fission-cli/fission_watch/)	 - Create, update and manage kube watcher
+* [fission workflow](/docs/reference/fission-cli/fission_workflow/)	 - Create, update and manage workflows
 

content/en/docs/reference/fission-cli/fission_function.md

@@ -27,6 +27,7 @@ Create, update and manage functions
 * [fission function create](/docs/reference/fission-cli/fission_function_create/)	 - Create a function (and optionally, an HTTP route to it)
 * [fission function delete](/docs/reference/fission-cli/fission_function_delete/)	 - Delete a function
 * [fission function describe](/docs/reference/fission-cli/fission_function_describe/)	 - Describe a function's health in one view (summary, conditions, build, pods)
+* [fission function dlq](/docs/reference/fission-cli/fission_function_dlq/)	 - Inspect and manage the async invocation dead-letter queue
 * [fission function get](/docs/reference/fission-cli/fission_function_get/)	 - Get function source code
 * [fission function getmeta](/docs/reference/fission-cli/fission_function_getmeta/)	 - Get function metadata
 * [fission function list](/docs/reference/fission-cli/fission_function_list/)	 - List functions