Rails Hotwire + Realtime

Use for Turbo/Stimulus/ActionCable architecture and reviews. Patterns from Campfire (cable-heavy chat) and Fizzy (streams-only kanban).

Choose the Right Realtime Architecture

Two proven 37signals topologies:

• Streams-only (Fizzy): no custom ActionCable channels at all. turbo_stream_from, broadcasts_refreshes + morph, lazy frames with ETags. Default to this for CRUD-ish apps.
• Cable-augmented (Campfire): custom channels only for lightweight JSON signals (presence, typing, unread pings) where rendering HTML server-side would be wasteful. Durable DOM state still goes through Turbo Streams.

Rule of thumb: Turbo Streams for anything that changes the DOM; bare ActionCable only for tiny ephemeral signals.

Turbo Defaults

• Prefer server-rendered partial updates over heavy client-side state systems.
• Set global morph refresh in the layout: turbo_refreshes_with method: :morph, scroll: :preserve.
• Use Turbo Streams for targeted updates; one action can render a multi-target stream template that updates every affected region atomically (source column + destination + detail pane).
• Lazy-load expensive sections with turbo_frame_tag ..., src:, loading: :lazy and give the frame endpoint its own fresh_when ETag. Extract frequently-changing fragments into their own frames so they don't bust the parent cache.
• Use data-turbo-permanent for elements that must survive navigation/morph (footer trays, in-progress editors).
• Block morph from clobbering client-owned state (e.g. localStorage-driven collapsed columns) via turbo:before-morph-attribute + preventDefault().
• Exempt realtime-heavy pages from Turbo's page cache (turbo_exempts_page_from_cache); rely on frame-level ETags instead.
• Optimistic UI without a JS framework: server-render a <template> partial with $placeholder$ tokens; client clones it with a generated ID before submit; the stream response replaces it.

Broadcast Patterns

• Keep broadcast logic on models (Message::Broadcasts concern with broadcast_create), not in controllers.
• Scope every stream name by tenant/user: [board.account, :all_boards], [user, :notifications] — stream names are isolation boundaries.
• Dual streams when needed: broadcasts_refreshes for direct subscribers plus broadcasts_refreshes_to ->(r) { [r.account, :aggregate_view] } for account-wide views.
• Gate noisy secondary broadcasts on meaningful change: set a flag in before_update when preview-relevant fields change; broadcast if: :preview_changed?.
• Suppress broadcasts in background jobs that incidentally touch records (Model.suppressing_turbo_broadcasts), e.g. around ActiveStorage analysis.
• Fan-out efficiently: render_to_string once, then broadcast_replace_to user, ..., html: per recipient.
• Use broadcast_*_later async variants when synchronous broadcasting hurts request latency.
• Broadcast-rendered partials lack request context: wrap attachment/url helpers (broadcast_image_tag pattern) so URLs resolve.

Reconnect & Catch-Up

• Catch-up over reload: on reconnect/tab-return, fetch a turbo-stream diff (?since=<epoch_ms>); server appends new records and replaces updated ones.
• An empty HeartbeatChannel gives reliable connected/disconnected callbacks for triggering catch-up and a debounced offline UI.
• Guard Stimulus connect() with a turbo-preview check so back/forward cache previews don't open sockets or request permissions.

Stimulus Defaults

• Keep controllers single-purpose; compose multiple small controllers on one element.
• Prefer targets/values over ad-hoc selectors and attribute parsing.
• Always clean up timers/listeners/subscriptions in disconnect. For cable subscriptions, defer unsubscribe one animation frame and skip if the element reconnected (morph churn).
• Use event dispatch between controllers (or outlets) instead of tight coupling.
• For complex surfaces, compose data-controller/data-action/target wiring in Ruby helpers (message_area_tag) so views stay declarative and the contract lives in one place.
• Read page context from <meta> tags into a tiny window.Current object rather than inlining JSON.
• Will elements added later via broadcast get the behavior? Design controllers to handle dynamically-inserted children (e.g. targetConnected callbacks).

Scroll & Interaction Contracts

• Preserve scroll declaratively: pass a custom attribute (maintain_scroll: true) on broadcasts and handle it once in a turbo:before-stream-render listener.
• Serialize competing scroll mutations through a promise queue when streams and optimistic inserts race.
• Strip a stream target's id on turbo:submit-start so background broadcasts can't race the form's own stream response.
• Infinite feeds: IntersectionObserver sentinels in turbo-stream pagination (remove trigger, append batch, append new sentinel); cap DOM size; only autoscroll when the user is at the latest page.

ActionCable / Connection Safety

• Authenticate in Connection#connect with the same identity resolution as HTTP; scope channel subscriptions through ownership (current_user.rooms.find_by(id: params[:room_id])).
• Disconnect deactivated/banned users remotely: ActionCable.server.remote_connections.where(current_user: user).disconnect.
• Presence: reference-count connections with a TTL (connections counter + connected_at, 60s freshness scope) to survive multi-tab and reconnects; debounce visibility changes (~5s) to avoid flicker.
• Under path-based tenancy, emit the cable URL from request.script_name via a custom meta tag helper.

Caching + Realtime

• Keep cache keys aligned with what affects output (record, user, timezone, filter state); use touch: true chains so child edits invalidate parents.
• Personalize cached fragments client-side: render data-creator-id, let a Stimulus controller compare against Current.user and toggle visibility — don't break fragment caching for per-user toggles.
• Avoid HTTP-caching form pages where token freshness is critical.

Web Push (when applicable)

• Push only to disconnected users, excluding the actor; respect per-user involvement levels (everything vs mentions-only).
• Deliver via a thread pool with persistent HTTP connections, resolving all AR data before posting to threads; invalidate expired subscriptions async.
• Clean up the push subscription client-side on logout.

Testing

• Model broadcasts: assert_turbo_stream_broadcasts([user, :notifications], count: 1) { ... } and assert_no_turbo_stream_broadcasts for negatives.
• Controller responses: as: :turbo_stream + assert_turbo_stream action: :replace, target: dom_id(...).
• For DOM-level assertions on broadcasts, a small helper reading ActionCable.server.pubsub.broadcasts + assert_select covers it.
• System tests: using_session("OtherUser") for multi-user realtime, and wait for turbo-cable-stream-source[connected] before asserting.

Red Flags

• Duplicate stream IDs/targets causing unstable updates.
• Broadcast channels or stream names that are not tenant/user-scoped.
• HTML rendering inside bare ActionCable channels (use Turbo Streams).
• Stimulus controllers leaking timers/listeners after navigation.
• Replacing full pages for small interactions that should be streamed.
• Custom ActionCable channels for things turbo_stream_from already does.
• Morph refreshes destroying in-progress user input (missing data-turbo-permanent).