Tutorial 9 Advanced

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Chapter 9 — Advanced deployment: arity, versioning, and migrations

The earlier chapters deployed a single app onto a small rig. This chapter is the operator/release-engineer reference for running Theia at scale over time:

9.1–9.4 Higher-arity deployment — one master + N workers, the machine-vs-role identity split, and how a single manifest fans out to a heterogeneous fleet.
9.5–9.8 Semantic versioning — what PATCH / MINOR / MAJOR mean for an app SWP, and the one-command way to cut each.
9.9–9.11 Config migration — the rules for changing an app's .art interface or its config without bricking a running board.

These three are one story: as arity grows and versions churn, the framework needs a stable identity per board and a disciplined way to evolve the interface. Read it once end-to-end; come back to a section when you cut a real release.

9.1 Arity: one master, N workers

A deployment's arity is how many machines it spans. Chapter 4 showed arity-1 (everything on one board) and a 2-machine split. The rule generalizes:

One master, N zonal workers. The master is the coordinator — it hosts the single per-cluster etcd, the deployment-wide singletons (per, sm, phm, com, vucm), and the mender gateway. Every other board is a zonal worker: the minimal per-board FC set (ucm + shwa) plus a mender agent that reaches the server through the master's proxy. One master + as many workers as your rig has.

The framework runtime ships this shape as a role-based rig you consume (you don't author it): manifest/services/rig.py exports RIG (master only) and MULTI (master + workers). A Distribution's roles pick which materialize onto which boards.

# arity-1: the single-master runtime (the common case)
theia manifest services

# arity-N: master + named workers
theia manifest services --attr MULTI

9.2 The identity split: role vs machine name

This is the single most important idea in a multi-board deploy. There are three identities, and conflating them is the classic mistake:

Identity	What it is	Unique?	Used for
role	`master` / `zonal` — the deployment identity	No (N workers share `zonal`)	which manifest slice colony provisions; whether the board runs etcd / a mender gateway vs agent
machine name	`master` / `compute` / `frontal` — the runtime identity	Yes	how `com`, the GUI, and `rtdb`/`tdb` address one specific board
hostname	the OS hostname	not guaranteed	never used as an identity — informational only

The rule: role is the deployment identity; the machine NAME is the runtime identity. Two workers can share the role zonal, but they must have distinct names (compute, frontal). Never use a role as a machine name — a rig with two machines both named zonal is rejected at serialize time (§9.4).

Why it matters: com on the master aggregates every board's supervisor tree into one view. To keep compute and frontal as distinct subtrees — and to let an operator type rtdb ps compute — each needs a unique name. The role (zonal) can't disambiguate them; the name can.

9.3 How a machine name resolves — `machine_index`

Each machine gets a stable cluster index at serialize time: the master is 0, workers are 1, 2, … in canonical order. The supervisor's own TIPC control node binds at type=0x80020001, instance=<machine_index> — so com discovers a supervisor at instance N and maps N → machine_index → the unique name.

The name→index map is written into machines.json (the one manifest com references):

// dist/manifest/machines.json  (arity-3 MULTI)
{
  "machines": ["master", "compute", "frontal"],
  "machine_index": { "master": 0, "compute": 1, "frontal": 2 },
  "role_map":      { "master": "master", "compute": "zonal", "frontal": "zonal" }
}

machine_index is authoritative — it wins over whatever a board's supervisor reports about itself, so a machine name is correct even mid-upgrade. On a deployed board, machines.json is staged into /opt/theia/config/, and the launcher points com at it (THEIA_MACHINE_MANIFEST=/opt/theia/config). Provisioning does both for you; you never wire it by hand.

Verify the identity end-to-end — from the master, list the cluster:

rtdb machines
# INST  MACHINE   PRESENT  HOST
# 0     master    yes      board-a
# 1     compute   yes      board-b
# 2     frontal   yes      board-c

rtdb ps compute     # scope to ONE board by its unique name
rtdb ps 2           # …or by its instance number

9.4 The identity invariants (enforced at serialize time)

theia manifest runs the TIPC address-collision gate, then three machine-identity invariants. A violation fails the serialize with a clear message — so a broken manifest never reaches a board:

Machine names are unique. (The name is the runtime identity.)
machine_index is sequential from 0 — 0, 1, 2, …, no gaps.
Index 0 is the master (the etcd coordinator).

theia manifest services --attr MULTI
# serialize-manifest: machine NAMES must be unique — … Duplicated: ['zonal'].
#   Give each board a distinct name (role master/zonal is the deployment
#   identity, NOT the name).

If you author your own multi-machine rig, give each worker a distinct name= and its role=Explicit("zonal"); the index + validation are automatic.

9.5 Semantic versioning of an app SWP

The runtime/base is installed once and held fixed; your app SWP is exchanged freely on top of it. Semver tells you how freely:

Bump	Example	Meaning	A free swap?
PATCH	`1.0.0 → 1.0.1`	bug fix, no interface change	Yes — deploy at will
MINOR	`1.0.0 → 1.1.0`	compatible, additive change	Yes
MAJOR	`1.0.0 → 2.0.0`	`.art` interface change (a proto / port / message contract)	No — needs a migration + a runtime pin

The dividing line is the .art interface. If the change is invisible at the .art level (you fixed a handler bug, tuned a constant), it's a PATCH/MINOR — a free overlay swap on the same runtime. If you changed a message, a port, or a node address in .art, it's a MAJOR: the wire contract moved, so it needs an explicit migration and it pins the runtime it was built against.

9.6 Cutting a PATCH — the free swap

theia release-swp <app> --patch mints the next patch of an app: it reads the app's latest published SWP, increments the PATCH, and builds + publishes the new artifact to the package plane. That new artifact is exactly what a Ground Station Rollout advances a device group onto.

# 1.0.0 already published → this cuts 1.0.1 and pushes it, abi-keyed
theia release-swp counter --patch --s3 http://10.0.0.99:9000
#   theia release-swp: counter 1.0.0 → v1.0.1 (patch bump)
#   published → s3://theia-swp/user-software/theia-rig/counter/1.0.1-amd64/

--from V — bump from an explicit base instead of "latest on S3".
--to V — set an explicit target version (skips the auto-bump).
The abi (amd64, bookworm-arm64, …) is baked into the artifact name, so a per-role Distribution resolves the right binary for each board — "partial per machine".

A PATCH ships no migration. On-device it's a clean overlay: the app's FC binaries are swapped, the supervisor re-reads its tree, done.

9.7 Cutting a MAJOR — `--migrate`

A MAJOR crosses the .art interface, so it is refused unless you acknowledge it with --migrate:

theia release-swp counter --to 2.0.0 --s3 http://10.0.0.99:9000
#   ✗ 2.0.0 crosses a MAJOR boundary … Re-run with --migrate to confirm.

--migrate makes two things mandatory, because a major is not a free swap:

A runtime pin — --requires-runtime <V>. A major app depends on exactly one runtime (its ABI/proto are pinned at build time). The Ground Station deploy gate refuses to install a pinned app onto a board whose base_version differs ("update the base first"). Refused if empty.
A migration file — --migration <path>, else the conventional apps/<app>/migrations/v<from>-to-v<to>.py. If none exists an empty no-op stub is auto-created for you to edit — a migration always ships, even if it's a no-op, so the upgrade is explicit and reviewable.

theia release-swp counter --to 2.0.0 --migrate \
  --requires-runtime 0.2.2-amd64 --s3 http://10.0.0.99:9000
#   theia release-swp --migrate: created empty migration stub
#     apps/counter/migrations/v1-to-v2.py — EDIT it, then re-run.

Edit the stub, re-run, and the migration is packed into the SWP (and synced to s3://theia-swp/.../migration/) as a first-class part of the artifact.

9.8 One artifact, one gate

The three release facts to keep straight:

PATCH / MINOR  →  free overlay swap, same runtime, no migration
MAJOR (--migrate)  →  runtime pin (requires_runtime) + a shippable migration/

The runtime pin is enforced twice — at a direct app publish and at a Rollout — so a major SWP can never land on the wrong runtime. That's what makes "exchange the app freely on a fixed runtime" safe: the framework knows which swaps are free and which aren't.

9.9 Config migration: the on-device rule

A MAJOR often needs to move on-device config or state across the interface break — rename a key, split a message, seed a new default. That is what the migration file is for. It runs on the board during install, before the new binaries take over:

ArtifactInstall on the board:
  1. unpack the new SWP
  2. run  migration/v1-to-v2.py <THEIA_ROOT>   ← against the STILL-OLD release
  3. overlay the new FC binaries
  4. merge the executor subtree + reload the supervisor

Running the migration first, against the old release, is deliberate: it can read the pre-upgrade config and rewrite it for the new interface. If the migration exits non-zero the install aborts and Mender rolls back — a broken migration never leaves a half-migrated board.

9.10 Writing a migration

The stub is a plain Python script — migrate(theia_root) invoked with the install root:

"""Migration counter v1 → v2 (MAJOR / .art interface change)."""
import json, sys, pathlib


def migrate(theia_root: str) -> None:
    cfg = pathlib.Path(theia_root) / "config" / "counter.json"
    if not cfg.is_file():
        return                                  # nothing installed yet — no-op
    data = json.loads(cfg.read_text())
    # v2 renamed `limit` → `max_count`; carry the operator's value across.
    if "limit" in data:
        data["max_count"] = data.pop("limit")
        cfg.write_text(json.dumps(data, indent=2))


if __name__ == "__main__":
    migrate(sys.argv[1] if len(sys.argv) > 1 else "/opt/theia")

Rules for a good migration:

Idempotent. It may run more than once (a retried install); running it twice must be a no-op the second time — check before you transform.
Tolerant of "not there yet." A fresh board may not have the old config — return cleanly, don't raise.
Fail loud on a real problem. A genuinely un-migratable state should exit non-zero — that aborts + rolls back, which is safer than a corrupt config.
Config, not code. It moves data; it never patches binaries (the SWP overlay does that).

9.11 What NOT to migrate — the plane boundary

The migration is app-plane only. It never touches the runtime/base — that plane is re-provisioned, never rolled, and carries no migration. Two consequences:

If your change needs a new runtime (a platform ABI bump), that's a base re-provision through colony — do it first, then deploy the app major that pins it (the runtime pin from §9.7 is what sequences this correctly).
A PATCH/MINOR has no migration by construction. If you find yourself wanting to migrate config for a "minor" change, it wasn't minor — the interface moved, so cut it as a MAJOR.

9.12 Node multiplicity — N clones of one node

Arity (§9.1) was about machines. Multiplicity is the same idea one level down: N instances of the same node type, in one process. Same code, same TIPC type, distinct instance — a worker pool.

You express it in .art with prototype (attribute-replacement — each clone is the base node, re-addressed to its own instance):

node atomic CounterNode { tipc type=0xd0010001 instance=0  config CounterConfig … }

// nine more clones at the same type, instances 1..9
node atomic Counter1 prototype CounterNode { tipc type=0xd0010001 instance=1 }
node atomic Counter2 prototype CounterNode { tipc type=0xd0010001 instance=2 }
// …

composition CounterProc {
    prototype CounterNode counter0   on process P1   // instance 0 — the base
    prototype Counter1    counter1   on process P1
    // …
}

Two things multiplicity gives you, and they use the instance differently:

1. A node knows its own instance. main resolves each clone's instance and hands it to the node (GenServerBase::tipc_instance()), so handler code can act on which clone it is:

void CounterNode::init(CounterNodeState&) {
    const uint32_t inst = this->tipc_instance();      // 0..9 — this clone
    // key THIS clone's config as "counter/<instance>"
}

2. Per-instance config. Each clone owns its config in per under <component>/<instance> (counter/0, counter/1, …). A change to counter/3 notifies only clone 3 — per reads the instance straight from the key and casts ConfigUpdated to that exact instance. No fan-out, no clone reading another's config. (Omit the instance and it's a single-instance node, the common case.)

Addressing a clone. TIPC addresses a node by (type, instance). Send to a specific instance to hit one clone; several ports co-bound at the same (type, instance) are round-robined by the kernel — that's how you build a load-balanced worker pool (bind the pool at one address) vs an addressable set (bind each at its own instance). Multiplicity gives you both shapes.

Poking a node — `theia cast` / `theia call`

For test/demo, drive a running node straight from the shell — pack a JSON payload into the node's proto message and send it over TIPC:

theia cast CounterNode Inc  --data '{"n": 5}'                 # send to the base
theia cast CounterNode Inc  --data '{"n": 100}' --instance 3  # ONE clone (inst 3)
theia call CounterNode Get  --instance 5                      # call → prints reply

--instance N targets clone N; --machine M shifts the instance by a board's machine index (the per-board clone on a /N deploy).
cast is fire-and-forget; call blocks for the reply and prints it as JSON.
No --instance sends to the node's base address (round-robined if the pool is co-bound).

It resolves <node> + <msg>/<op> from your workspace's .art, so any node you model is reachable — a one-liner instead of a probe script or an rf test.

The in-repo tutorial_ws carries the 10-CounterNode composition above as the worked example: build it, then theia cast CounterNode Inc --instance 3 and watch [counter3] Inc (inst 3) → count=… in its log.

9.13 Running the ARA services locally — `theia init --with-services`

Every earlier chapter used a bare workspace (theia init): the supervisor + your own apps, no ARA platform services. That is the normal app-developer setup — your app reaches the platform (config via per, state via sm, …) over TIPC at runtime, and those services run where the platform runs (a provisioned board, or a local docker-compose rig), NOT inside your app workspace.

theia init --with-services is the advanced, single-slice case: it symlinks the framework's service FCs into your workspace so theia start brings up the whole platform (com/log/per/sm/ucm/shwa + your apps) as one supervised tree on one TIPC namespace. Use it only when you deliberately want the app and the platform co-located on a single TIPC slice — e.g. an all-in-one dev box or a CI smoke test — rather than the normal split where the platform is a separate deploy.

theia init --with-services          # symlinks system/services → $THEIA_ROOT
theia manifest bootstrap
theia install bootstrap             # stages supervisor + all service FCs
theia start                         # the full platform + your apps, one tree

Two things to know:

One TIPC namespace = one platform. host-network docker containers share a single TIPC nametable, so a --with-services workspace and a docker-compose platform rig on the same host collide at the service addresses. Run one or the other on a given slice — or isolate them with a per-rig TIPC cluster id (Machine.tipc_cluster_id). The common pattern is: the compose rig owns the platform slice, and your app workspace does a bare theia init and joins that slice, rather than starting a second platform.
per needs etcd; nm needs CAP_NET_ADMIN. A local --with-services start without etcd (or netadmin) will see per retry / nm fail. Either point per at a running etcd, or keep those services defined but down so the rest of the tree still comes up clean. theia install deep-merges a per-machine override onto the staged supervisor tree, so drop a deploy/config/<machine>/executor.json in your workspace:
```
{"children":[{"name":"services_sup","children":[
   {"name":"per","run_on_start":false},
   {"name":"nm", "run_on_start":false}]}]}
```
Re-run theia install and those FCs stay defined but not booted (the supervisor logs run_on_start=false — defined, not started at boot), while com/sm/the rest start normally.

You now have: the higher-arity model (one master + N uniquely-named workers, the role-vs-name split, and the serialize-time invariants that keep identity clean); the semver rules for an app SWP (PATCH/MINOR are free swaps, MAJOR pins a runtime and ships a migration); the on-device config-migration contract (runs first, against the old release, idempotent, aborts on failure, app-plane only); and node multiplicity (N clones of one node, each knowing its instance + owning its per-instance config, poked from the shell with theia cast/call).

Next: you have finished the tutorial. Revisit Chapter 5 to bind a specific runtime + SWP version into a Distribution, and Chapter 6 to deploy it across a multi-board fleet.

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Tutorial 9 Advanced

Chapter 9 — Advanced deployment: arity, versioning, and migrations

9.1 Arity: one master, N workers

9.2 The identity split: role vs machine name

9.3 How a machine name resolves — machine_index

9.4 The identity invariants (enforced at serialize time)

9.5 Semantic versioning of an app SWP

9.6 Cutting a PATCH — the free swap

9.7 Cutting a MAJOR — --migrate

9.8 One artifact, one gate

9.9 Config migration: the on-device rule

9.10 Writing a migration

9.11 What NOT to migrate — the plane boundary

9.12 Node multiplicity — N clones of one node

Poking a node — theia cast / theia call

9.13 Running the ARA services locally — theia init --with-services

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9.3 How a machine name resolves — `machine_index`

9.7 Cutting a MAJOR — `--migrate`

Poking a node — `theia cast` / `theia call`

9.13 Running the ARA services locally — `theia init --with-services`