I've deployed a few different Elixir services to the hosting platform https://render.com and found their provided documentation to be lacking for real-world Phoenix apps. Especially if you're using Live View. Here's an augmentation to their guide with the extra steps you might be missing.

Initial Setup

Follow the official guide: https://render.com/docs/deploy-phoenix but don't deploy your service yet. You'll need to make some changes:

Add Evars

Add some new evars:

• ELIXIR_VERSION = 1.10.3 or whatever version you like. But the default version is older and breaks the build for new Elixir apps
• DATABASE_URL = The connection string for the database you'll be using

Migrations

After, do these things. MAKE SURE YOU REPLACE WITH YOUR APP NAME :

• Add a new script for running migrations (./build_and_migrate.sh):

#!/usr/bin/env bash
# exit on error
set -o errexit

./build.sh

# Run migrations
_build/prod/rel/<app_name>/bin/<app_name> eval "Render.Release.migrate"

• Make that new script executable.
• Make a module in your application for running migrations (lib/<app_name>_web/render_release.ex):

defmodule Render.Release do
  @moduledoc """
    Responsible for custom release commands
  """
  @app :<app_name>

  def migrate do
    # Allows the migration script to connect to a database using SSL.
    Application.ensure_all_started(:ssl)

    for repo <- repos() do
      {:ok, _, _} = Ecto.Migrator.with_repo(repo, &Ecto.Migrator.run(&1, :up, all: true))
    end
  end

  def rollback(repo, version) do
    # Allows the migration script to connect to a database using SSL.
    Application.ensure_all_started(:ssl)

    {:ok, _, _} = Ecto.Migrator.with_repo(repo, &Ecto.Migrator.run(&1, :down, to: version))
  end

  defp repos do
    Application.load(@app)
    Application.fetch_env!(@app, :ecto_repos)
  end
end

• Change the deploy command for your render app to be ./build_and_migrate.sh instead of ./build.sh

Using a Database that Requires SSL

Unless you're using a private database on Render, you'll want to connect to your PG instance using SSL. To do that, you've got to

• Uncomment the line in releases.exs that says ssl: true for your app's repo:

...
config :<app_name>, <AppName>.Repo,
  ssl: true, <-- this line, it's commented by default.
  url: database_url,

And then

• Add the :ssl application to extra_applications in mix.exs:

def application do
    [
      mod: {<AppName>.Application, []},
      extra_applications: [:logger, :runtime_tools, :ssl] <-- added :ssl to the end of this list.
    ]
  end

Troubleshooting

If you run into an issue with Phoenix Live View breaking and reloading the page every few seconds, you might have enabled force_ssl in your endpoint, and it could be trying to redirect your web socket traffic to an https scheme. Which is strange. I ran into this once, and haven't found a great workaround for it.

PgBouncer

If your database does pooling using pg_bouncer then open up releases.exs and add prepare: :unnamed to your repo config.

config :<app_name>, <AppName>.Repo,
  ssl: true,
  url: database_url,
  pool_size: String.to_integer(System.get_env("POOL_SIZE") || "10"),
  prepare: :unnamed <-- this line!