RamalLive

A LiveView inspector for Ramal branches. Not on Hex yet.

It shows the open and proposed branches of one Ash domain as columns. Each column has the branch's name, status, age and overlay size, and its Ramal.diff/1 as before and after rows. Buttons fork, merge and discard an open branch and approve or reject a proposal; merge, discard, approve and reject ask for a second click first. While the page is open, Ramal's telemetry updates the columns, and only the branch that changed is read again.

There is no JavaScript, no Tailwind and no asset pipeline. The page is a LiveView with inline CSS (slate for the base line, copper for branches, light and dark themes), mounted by your router inside your own live_session, so it uses your LiveView socket and your JavaScript. The decision is in ADR 0015.

Setup

Requires Phoenix 1.7+, Phoenix LiveView 1.1+ and a running Phoenix.PubSub.

# mix.exs: not on Hex yet, so use a checkout of this repository, which holds both packages
{:ramal, path: "../ramal"},
{:ramal_live, path: "../ramal/ramal_live"}

# application.ex, after the PubSub and Ramal.Supervisor, in every node that runs branches
{RamalLive.Broadcaster, pubsub: MyApp.PubSub}

# router.ex, behind your own authorization
import RamalLive.Router

scope "/admin" do
  pipe_through [:browser, :require_admin]

  live_session :admin, on_mount: [{MyAppWeb.UserAuth, :ensure_admin}] do
    ramal_inspector "/ramal", domain: MyApp.Farm, pubsub: MyApp.PubSub, actor: {MyAppWeb.Inspector, :actor}
  end
end

Options of ramal_inspector/2: :domain, :pubsub and :actor (all required) and :debounce (milliseconds, default 50). :actor is {module, function}; the page calls module.function(socket) and uses the result as the actor that is recorded as decided_by and replays a merge, or refuses to act when it returns nil. A router without it does not compile. For a development tool with no users, return a constant (def actor(_socket), do: :dev).

Things to know

• Authorization is yours. Whoever opens the page can merge and discard any branch of the domain. Ramal records who decided and never checks. Mount it behind your own authentication in a live_session with an on_mount that checks the same, and give :actor (required) so decisions have a decider: when that function returns nil the page refuses every action. Mounts that differ in who may use them need separate live_sessions, because the page reads its options from the URL the browser joins with. SECURITY.md has the whole list.
• Secrets. Attributes marked sensitive?: true show as [redacted] in the diff.
• Fonts. Headings ask for Barlow Condensed and data for IBM Plex Mono. The page loads neither; add the link tag to your root layout if you want them, or the system's condensed and monospace fonts are used.
• Content security policy. The CSS is an inline <style>; a policy without style-src 'unsafe-inline' blocks it.
• Reading loads branches. The page reads each branch it shows with Ramal.get/1, which starts its process if it was unloaded; it unloads again after idle_timeout. A column shows the first 100 changes and counts the rest.
• Without the broadcaster the page works but only changes after an action made on it or on Reload, and says so.
• Telemetry. Every read of a branch emits [:ramal_live, :column, :read] with %{branch_id, domain} metadata and a duration measurement.

Try it

A runnable demo, the one to record the GIF from, lives in examples/farm_demo.exs. It is a single file that installs its own dependencies with Mix.install (so the first start compiles for a few minutes), runs a Phoenix Playground app on a seeded farm in Postgres, and mounts the inspector with the ramal_inspector line above.

docker compose up -d db                 # from the repository root: Postgres on port 5435
elixir ramal_live/examples/farm_demo.exs

Open http://localhost:4000 and press Explore 4 alternatives. Four branches open one after the other, each moves herd R7 out of paddock L07 into a different paddock, and the columns fill in as the writes happen. Merge one: the database now has R7 in its new paddock, and merging any other column is refused as stale, because that branch read R7 where it used to be. Reset discards every branch and seeds the farm again.

The demo uses a ramal_dev database on the server of the test database, creates it if it is missing, and drops and recreates its three tables on every start, so do not point it at data you want to keep. RAMAL_PG_HOST, RAMAL_PG_PORT, RAMAL_PG_USER and RAMAL_PG_PASSWORD change the server and PORT changes the HTTP port. Branches are kept in ETS, so they do not survive a restart. The page is the demo's own LiveView with the inspector in an iframe, so one URL shows both the button and the columns.

Development

cd ramal_live
mix deps.get
mix ci          # format, compile with warnings as errors, credo strict, tests

The tests run on a test endpoint with Phoenix.LiveViewTest and an ETS-backed domain, so no database is needed.