231 lines
19 KiB
Markdown
231 lines
19 KiB
Markdown
# Design Document — controller-status (`ctrlstatus`)
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## Overview
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**Purpose:** add a single, cheap, read-only client→controller query — `ctrlstatus`, an XCE analog of LSF `lsid` — that returns basic cluster/controller identity and health: who is the current primary, the answering node's identity and role, the configured controllers (peers), the committed configuration version and content checksum, and a few HA health/progress fields (term, commit/apply position, fenced state, cluster name).
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**Users:** operators inspecting a running cluster, and test/E2E authors orchestrating failover (including `wait-primary`, which switches its probe to this query).
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**Impact:** today there is no status query — callers infer "is there a serving primary" indirectly (e.g. by listing jobs). This adds a new opcode by cloning the existing **opcode-only read** pattern of `clusterconf`, reads only already-maintained HA/config state (no behavior change), and crucially makes the query answerable on **any** node by adding it to the HA dispatch-gate allow-lists.
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### Goals
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- A new read-only opcode returning the status fields of Requirements 2–6 in one request/response (1.1, 1.4).
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- Answerable on **any** node and across failover — a standby reports the primary it knows (2.3, 7.1–7.3).
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- Report a content checksum of the committed configuration so same-version divergence is detectable (5.2, 5.3).
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- A `ctrlstatus` test-client command (8.x) and a `wait-primary` probe switched to this query (9.x).
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### Non-Goals
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- No operator-facing CLI/REST `lsid` surface (Go tier) — later pass.
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- No change to HA election, replication, or commit behavior — the query only **reads** existing state.
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- No new configuration checksum computation — the committed-config SHA-256 already exists; this only exposes it.
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## Boundary Commitments
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### This Spec Owns
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- A new Cap'n Proto opcode `ctrlstatus` and its reply payload (`CtrlStatus`, `CtrlPeer`).
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- The controller handler `handle_ctrlstatus` that snapshots local HA/config state into the reply.
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- The **dispatch-gate allow-list entries** that let `ctrlstatus` answer in every controller role (incl. no-quorum).
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- The libxce client API (`xce_ctrlstatus_req` / `xce_ctrlstatus` / `xcecli_ctrlstatus` + free helper).
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- The `ctrlstatus` test-client command and the `wait-primary` probe switch.
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### Out of Boundary
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- The Go CLI/REST `lsid` surface (later spec).
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- Any change to how HA state (role, term, primary identity, committed config tag, commit/apply LSN, fence) is **produced or maintained** — this spec only reads it.
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- The existing `clusterconf` opcode and its resource/queue/worker payload (left unchanged).
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### Allowed Dependencies
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- The Cap'n Proto schema + build-time codegen (`src/schema/controller.capnp` → generated `controller.capnp.h/.c`).
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- The existing request/reply plumbing (`init_reply_by_req`, `xce_reply`, opcode-only `*_req` senders) and client failover wrapper (`XCECLI_FAILOVER_CALL`, `is_write=false`).
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- Read access to existing HA state (`ha_state_t`), config (`myconf_t`: `committed_config_tag`, `config_sha256`, `peers_cfg`), and persist accessors (`persist_recovery_unrecoverable`, `persist_durable_lsn`).
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### Revalidation Triggers
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- Any change to the `CtrlStatus`/`CtrlPeer` reply shape or the `ctrlstatus` opcode ordinal → re-check libxce decode + the test command + any future consumer.
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- Any change to the dispatch-gate role allow-lists → re-check that `ctrlstatus` still answers in every role and that no other opcode's gating widened.
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- A change to the meaning of `committed_config_tag` / `config_sha256` → re-check the version/checksum fields.
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## Architecture
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### Existing Architecture Analysis
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- **Opcode-only read precedent:** `clusterconf` is sent with no request body (`Request_body_nomsg`), dispatched in `cluster.c` `switch(request.opcode)`, handled by `handle_clusterconf` (`reply.c:10`), and returned via `xce_reply`. The client side is `xce_clusterconf` → `xcecli_clusterconf` (`XCECLI_FAILOVER_CALL`, `is_write=false`). **`ctrlstatus` clones this pattern.**
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- **No-alloc state-report precedent:** `ha_nop_reply_state_report` (`ha.c:1784`) reads HA atomics into a stack struct and points the reply union at it without heap allocation. `handle_ctrlstatus` follows this model (a small bounded peer list is the only allocation).
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- **Dispatch gate (the critical seam):** `ha_dispatch_gate` (`ha.c:2059`) is an allow-list keyed by role. The `CTRL_STANDBY` branch defaults to `-XCE_ERR_STANDBY`; `CTRL_INIT`/`CTRL_ELECTING` default to `-XCE_ERR_NOT_READY`; the `CTRL_PRIMARY` no-quorum branch allow-lists only specific reads. `clusterconf` is **not** in any standby allow-list — it is implicitly primary-only-when-serving. A status query must **not** inherit that; it must be explicitly allow-listed in every role branch.
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- **Config content checksum already exists:** `config_version_tag` = first 8 bytes of SHA-256 over the committed config blob; full digest in `config_sha256[32]`, round-trip-verified on load (`config_repl.c`).
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### Pattern & dependency direction
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Extend-in-place along the existing request path. Dependency direction (unchanged): `schema → libxce (request/reply/client) → controller handler`; the test client depends on libxce. No upward dependencies introduced.
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```mermaid
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graph LR
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TestClient[xce_test ctrlstatus / wait-primary] --> Libxce[libxce xcecli_ctrlstatus]
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Libxce --> Failover[XCECLI_FAILOVER_CALL is_write false]
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Failover --> Gate[ha_dispatch_gate allow-list all roles]
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Gate --> Handler[handle_ctrlstatus snapshot local state]
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Handler --> HAState[ha_state_t and myconf_t read-only]
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Handler --> Reply[xce_reply CtrlStatus]
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```
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## File Structure Plan
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### Modified Files
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- `src/schema/controller.capnp` — add `OPCode ctrlstatus @40`; new `struct CtrlStatus $C.mapname("xce_ctrlstatus_t")` and `struct CtrlPeer $C.mapname("xce_ctrlpeer_t")`; reply-union member `ctrlstatus @17: CtrlStatus`. (Build regenerates `controller.capnp.h/.c` → `xce_ctrlstatus_t`, `RequestReply_data_ctrlstatus`, `free_CtrlStatus`.)
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- `src/controller/reply.c` — add `handle_ctrlstatus` (snapshot local HA/config state into a `CtrlStatus` reply; small peer list; `xce_reply`). Mirrors `handle_clusterconf`/`ha_nop_reply_state_report`.
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- `src/controller/cluster.c` — add `case OPCode_ctrlstatus: rc = handle_ctrlstatus(...)` to the opcode switch.
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- `src/controller/ha.c` — add `OPCode_ctrlstatus` to the `ha_dispatch_gate` allow-lists for `CTRL_PRIMARY` (incl. the no-quorum branch), `CTRL_STANDBY`, `CTRL_ELECTING`, `CTRL_INIT`. **(the requirements-critical change)**
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- `src/lib/request.c` + `src/include/request.h` — add `xce_ctrlstatus_req` (opcode-only sender, clone of `xce_clusterconf_req`).
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- `src/lib/xceapi.c` — add `xce_ctrlstatus` (send req, `cbuf_get` status, `MOVE_PTR` reply union).
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- `src/lib/client.c` + `src/include/client.h` — add `xcecli_ctrlstatus` (`XCECLI_FAILOVER_CALL`, `is_write=false`) and the `xcecli_free_ctrlstatus` macro.
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- `src/controller/testsuite/test.c` — add `cmd_ctrlstatus` + table registration; switch `cmd_wait_primary`'s probe (currently `joblist_query(...)` at the deadline-loop call site) to `xcecli_ctrlstatus`.
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### New Files
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- None (capnp C types are generated; all handlers/APIs slot into existing TUs).
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## System Flows
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### Status query (any role) + dispatch gate
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```mermaid
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sequenceDiagram
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participant C as Client
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participant F as Failover wrapper
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participant N as Controller node
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participant G as ha_dispatch_gate
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participant H as handle_ctrlstatus
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C->>F: xcecli_ctrlstatus
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F->>N: ctrlstatus request (opcode-only)
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N->>G: gate(opcode, role)
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G-->>N: ALLOW (all roles, incl no-quorum)
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N->>H: snapshot local state
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H-->>C: CtrlStatus reply
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Note over C,N: On a standby, primaryName = its known primary (or "unknown"); responderRole = STANDBY
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```
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Gate decision: `ctrlstatus` is allow-listed in every role branch and does not require quorum or a committed read — it returns the node's local view even when fenced or without quorum (precisely when an operator most wants it).
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### wait-primary probe (Req 9)
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`wait-primary` keeps its existing monotonic-deadline poll loop and timeout/exit semantics; only the probe changes from `joblist_query` to `xcecli_ctrlstatus`. Success predicate: the status reply reports a **non-`"unknown"`** current primary. On success it prints the served primary's identity. (Rationale + caveat below.)
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## Requirements Traceability
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| Requirement | Summary | Components | Interfaces |
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|-------------|---------|------------|------------|
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| 1.1, 1.2, 1.4 | Single-call read-only focused status | `handle_ctrlstatus`, `CtrlStatus` schema | opcode `ctrlstatus`, reply `CtrlStatus` |
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| 1.3 | "unknown" for undeterminable fields | `handle_ctrlstatus` | empty Text/sentinel mapping |
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| 2.1, 2.2, 2.3 | Current primary identity (unknown when unelected; standby's known primary) | `handle_ctrlstatus` (reads `ha->primary_host` under `ha->lock`) | `CtrlStatus.primaryName` |
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| 3.1, 3.2, 3.3 | Answered-by node + role, distinct from primary | `handle_ctrlstatus` | `CtrlStatus.responderName`, `responderRole` |
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| 4.1, 4.2 | Configured controllers + count | `handle_ctrlstatus` (reads `peers_cfg`) | `CtrlStatus.peers`, `peerCount` |
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| 5.1, 5.2, 5.3 | Config version + content checksum | `handle_ctrlstatus` (reads `committed_config_tag`, `config_sha256`) | `CtrlStatus.configVersion`, `configChecksum` |
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| 6.1–6.4 | Term, commit/apply, fenced, cluster name | `handle_ctrlstatus` | `CtrlStatus.term`, `committedLsn`, `appliedLsn`, `fenced`, `clusterName` |
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| 7.1, 7.2, 7.3 | Failover-aware any-node delivery | `xcecli_ctrlstatus`, dispatch-gate allow-lists | `XCECLI_FAILOVER_CALL` (is_write=false), gate entries |
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| 8.1, 8.2, 8.3 | Test-client `ctrlstatus` command | `cmd_ctrlstatus` | client command + exit code |
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| 9.1–9.4 | wait-primary uses the status query | `cmd_wait_primary` probe swap | `xcecli_ctrlstatus` |
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## Components and Interfaces
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| Component | Layer | Intent | Req Coverage | Key Dependencies | Contracts |
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|-----------|-------|--------|--------------|------------------|-----------|
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| `CtrlStatus`/`CtrlPeer` schema | Schema | Reply payload for the status query | 2–6 | capnp codegen (P0) | API (reply) |
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| `handle_ctrlstatus` | Controller | Snapshot local HA/config state into the reply | 1–6 | `ha_state_t`, `myconf_t`, persist accessors (P0) | Service |
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| dispatch-gate allow-lists | Controller HA | Permit `ctrlstatus` in every role | 7 | `ha_dispatch_gate` (P0) | Service |
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| `xce_ctrlstatus` / `xcecli_ctrlstatus` | libxce | Failover-aware client call + free | 1, 7 | failover wrapper (P0) | Service |
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| `cmd_ctrlstatus` | Test client | Print the status | 8 | `xcecli_ctrlstatus` (P0) | State |
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| `cmd_wait_primary` probe | Test client | Use status as the serving-primary probe | 9 | `xcecli_ctrlstatus` (P0) | State |
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### Schema — reply payload (Cap'n Proto)
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```capnp
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struct CtrlPeer $C.mapname("xce_ctrlpeer_t") {
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name @0: Text;
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host @1: Text;
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port @2: UInt32;
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}
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struct CtrlStatus $C.mapname("xce_ctrlstatus_t") {
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clusterName @0: Text;
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primaryName @1: Text; # empty ⇒ "unknown" (no elected/known primary)
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responderName @2: Text; # the node that answered
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responderRole @3: UInt8; # ctrl_role_t: INIT/ELECTING/PRIMARY/STANDBY
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term @4: UInt64;
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configVersion @5: UInt64; # committed_config_tag (8-byte SHA-256 prefix)
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configChecksum @6: Data; # full committed-config SHA-256 (32 bytes)
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committedLsn @7: UInt64;
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appliedLsn @8: UInt64;
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fenced @9: Bool; # in_catch_up OR recovery_unrecoverable
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peers @10: List(CtrlPeer) $C.mapname("peers.list") $C.maplistcount("peers.count");
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peerCount @11: UInt32;
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}
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```
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- New OPCode ordinal: `ctrlstatus @40` (next free after `preVoteReply @39`). New reply-union member: `ctrlstatus @17` (next free after `walackreplymsg @16`). Field ordinals are append-only — never reuse/reorder.
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#### `handle_ctrlstatus` — Service contract
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| Field | Detail |
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|-------|--------|
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| Intent | Build a `CtrlStatus` from the responding node's local HA/config state and reply |
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| Requirements | 1.1–1.4, 2.1–2.3, 3.1–3.3, 4.1–4.2, 5.1–5.3, 6.1–6.4 |
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**Responsibilities & Constraints**
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- Read-only: must not modify any HA, persist, or config state (1.2).
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- Field sourcing: `clusterName`/`responderName` from `c->myconf`/own peerinfo; `responderRole`, `term`, `appliedLsn`, `committedLsn`, `committed_config_tag` via `atomic_load_explicit(..., acquire)`; `primaryName`/peers as below; `fenced = in_catch_up || persist_recovery_unrecoverable(...)`; `configChecksum` from `config_sha256[32]`.
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- **Locking:** `primary_host`/`primary_port` are guarded by `ha->lock` — take it for a consistent snapshot, copy out, release. All other fields are atomics or immutable config.
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- **"unknown" mapping (1.3, 2.2, 2.3):** if `primary_host[0] == '\0'` (no known primary), emit an empty `primaryName`, which the client renders as `"unknown"`.
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- **Peers (4.x):** iterate `c->myconf->peers_cfg.candidates[0..count-1]` → one `CtrlPeer{name,host,port}` each; set `peerCount`.
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- Answerable in every role; returns the local view even when fenced/no-quorum.
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**Dependencies**
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- Inbound: `cluster.c` opcode switch — routes the request (P0).
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- Outbound: `ha_state_t`, `myconf_t`, persist accessors — read-only snapshot (P0).
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- Outbound: `init_reply_by_req`, `xce_reply` — reply encode/send (P0).
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#### Dispatch-gate allow-lists — Service contract
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- Add `OPCode_ctrlstatus` to the allow-list in `ha_dispatch_gate` for `CTRL_PRIMARY` (including the no-quorum branch), `CTRL_STANDBY`, `CTRL_ELECTING`, and `CTRL_INIT` (7.1, 7.2).
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- Constraint: the change is scoped strictly to `ctrlstatus`; no other opcode's gating may widen. `ctrlstatus` never requires quorum or a committed read.
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#### libxce client API — Service contract
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```c
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/* opcode-only request sender (clone of xce_clusterconf_req) */
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int xce_ctrlstatus_req(endpoint_t* ep);
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/* send + await reply; on success MOVE_PTR the reply union out */
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int xce_ctrlstatus(xce_ctx_t* ctx, xce_ctrlstatus_t** status);
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/* failover-aware read (is_write=false) */
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int xcecli_ctrlstatus(xcecli_ctx_t c, xce_ctrlstatus_t** status);
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#define xcecli_free_ctrlstatus(s) xce_free_ctrlstatus(s)
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```
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- Preconditions: valid client context.
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- Postconditions: on success `*status` owns a decoded `CtrlStatus` (caller frees); on failure returns a typed negative (7.3) and `*status` untouched.
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- Invariants: `is_write=false` — retryable/rotatable across the configured controllers.
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#### `cmd_ctrlstatus` (test client) — State contract
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- Calls `xcecli_ctrlstatus`; on success prints the fields in human-readable form (8.1), framing the responder as `answered by <responderName> (<role>)` distinct from `Primary:` (3.3); renders empty `primaryName` as `unknown`; renders `configChecksum` as hex. Returns 0 on success, `<0` on failure with the error printed (8.2, 8.3). Frees the reply.
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#### `cmd_wait_primary` probe swap — State contract
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- Replace the single `joblist_query(...)` probe call in the deadline loop with `xcecli_ctrlstatus`.
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- **Success predicate (9.1, 9.2):** the status reply reports a non-`"unknown"` `primaryName`. On success, complete and print the served primary's identity.
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- **Preserved (9.4):** the timeout-argument parsing, monotonic deadline, poll interval, log-level quieting, and success/failure exit codes are unchanged; only the probe call and the success message change.
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- **Decision & caveat:** the predicate is "a known primary is reported" rather than "the responder is itself the primary," because the failover read may legitimately be answered by a standby; requiring `responderRole == PRIMARY` could starve the predicate if a standby always answers first. The accepted caveat is a brief window where a standby may report a just-failed primary before it clears; this is acceptable for a "wait until a primary exists" gate and is strictly more informative than the prior job-list probe (it names the primary).
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## Data Models
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The only new data is the reply payload above. `CtrlStatus` is a flat value object (no persistence, no aggregate); `CtrlPeer` is a bounded value list (≤ configured controller count, typically 3). `configChecksum` is the 32-byte committed-config SHA-256; `configVersion` is its 8-byte prefix as a `UInt64`. Two nodes with identical committed config content produce identical `configChecksum` and `configVersion`; differing content differs in both (5.3).
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## Error Handling
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- **No reachable controller (7.3):** `xcecli_ctrlstatus` returns the failover wrapper's typed negative (e.g. no-master/timeout); `cmd_ctrlstatus` prints it and returns non-zero (8.3); `wait-primary` keeps polling until its deadline (9.3).
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- **Undeterminable field (1.3):** emit the defined "unknown"/empty value, never uninitialized data.
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- **Standby with no known primary (2.3):** `primaryName` empty → "unknown"; the call still succeeds (the status itself is valid).
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- **Read-only guarantee (1.2):** the handler takes only read locks/atomic loads; no state mutation on any path.
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## Testing Strategy
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### Unit / handler
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- `handle_ctrlstatus` on a PRIMARY returns `primaryName==self`, `responderRole==PRIMARY`, populated peers/version/checksum (2.1, 3.x, 4.x, 5.x).
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- `handle_ctrlstatus` on a STANDBY with a known primary returns that primary and `responderRole==STANDBY`; with no known primary returns empty `primaryName` (2.2, 2.3).
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- `fenced` reflects `in_catch_up`/`recovery_unrecoverable` (6.3); the handler mutates no state (1.2).
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- `configChecksum`/`configVersion` equal across two nodes with identical config, differ when content differs (5.3).
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### Integration
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- Dispatch-gate: a `ctrlstatus` request is answered (not `-XCE_ERR_STANDBY`/`-XCE_ERR_NOT_READY`) on STANDBY, ELECTING, INIT, and PRIMARY-no-quorum nodes; no other opcode's gating changed (7.1, 7.2).
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- libxce round-trip: `xcecli_ctrlstatus` decodes all fields; `is_write=false` rotates across configured controllers; no-reachable-controller returns a typed failure (7.3).
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### E2E (live `/xce-deploy-ha`)
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- `ctrlstatus` against a healthy 3-node cluster prints the primary, peers, version+checksum; querying a standby still reports the primary (2.3, 8.1).
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- `wait-primary` (status-probe) returns immediately on a healthy cluster and names the primary; after a primary kill, blocks until a new primary is reported, then names it; times out when none (9.1–9.4). Directly useful to the `ha-commit-durability` Phase 6 liveness/>60s-election investigation.
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## Security Considerations
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`ctrlstatus` exposes cluster topology, role, term, and config version/checksum — the same trust level as the existing `clusterconf`/state-report reads (no secrets, no config content, no job data). It is read-only and goes through the same authenticated client path as other client ops; no new authorization surface is introduced. Broadening the dispatch gate is scoped strictly to this one read opcode.
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