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igmarin/elixir-phoenix-skills

Curated library of 38 atomic skills, 7 personas, and 1 orchestrator for Elixir and Phoenix development. Organized by category: fundamentals, phoenix, database, testing, auth, infrastructure, quality, security, integrations, tooling, frameworks, personas, and orchestration. Covers core Elixir patterns, Phoenix LiveView, Ecto, OTP, Oban, testing, security, deployment, real-time, and modern tooling (Req, Swoosh, Cachex, Broadway, Ash).

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SKILL.mdskills/infrastructure/oban-essentials/

name:
oban-essentials
type:
atomic
tags:
atomic
license:
MIT
description:
MANDATORY for ALL Oban work. Invoke before writing workers or enqueuing jobs. Covers worker definition, enqueuing, return values, queue configuration, idempotency, unique jobs, scheduled/recurring jobs, pruning, testing with Oban.Testing, and arg best practices. Trigger words: Oban, worker, job, queue, enqueue, perform, cron, idempotent, background job.
metadata:
{"user-invocable":"true","version":"1.0.0","adapted-from":"j-morgan6/elixir-phoenix-guide","original-author":"Joseph Morgan"}

Oban Essentials

Use this skill before writing ANY Oban worker or enqueuing jobs.

End-to-End Workflow

When setting up a new Oban worker, follow these steps in order:

  1. Add queue to config — define the queue name and concurrency in config/config.exs
  2. Define worker module — use Oban.Worker with explicit queue, max_attempts, and unique options
  3. Enqueue from context — call Oban.insert/1 inside a context function, not a LiveView
  4. Write tests — use Oban.Testing with assert_enqueued and perform_job, covering all return paths

RULES — Quick Reference

  1. use Oban.Worker with explicit queue and max_attempts — see Worker Definition
  2. Make workers idempotent — the same job may execute more than once — see Idempotency
  3. Never put large data in job args — store IDs and fetch fresh data in the worker — see Job Args Best Practices
  4. Use Oban.insert/1 (not Oban.insert!/1) and handle the error tuple — see Enqueuing Jobs
  5. Enqueue from contexts, not LiveViews — keep the web layer thin — see Enqueuing from Contexts

Worker Definition

defmodule MyApp.Workers.SendWelcomeEmail do
  use Oban.Worker,
    queue: :mailers,
    max_attempts: 3,
    unique: [period: 300, fields: [:args], keys: [:user_id]]

  @impl Oban.Worker
  def perform(%Oban.Job{args: %{"user_id" => user_id}}) do
    case MyApp.Accounts.get_user(user_id) do
      nil ->
        {:cancel, "user #{user_id} not found"}

      user ->
        MyApp.Mailer.send_welcome(user)
        {:ok, :sent}
    end
  end
end

Enqueuing Jobs

# Basic insert — always handle the result
case MyApp.Workers.SendWelcomeEmail.new(%{user_id: user.id}) |> Oban.insert() do
  {:ok, job} -> {:ok, job}
  {:error, changeset} -> {:error, changeset}
end

# Schedule for later
%{user_id: user.id}
|> MyApp.Workers.SendWelcomeEmail.new(schedule_in: 3600)
|> Oban.insert()

❌ Bad — raises on failure:

MyApp.Workers.SendWelcomeEmail.new(%{user_id: user.id}) |> Oban.insert!()

Enqueuing from Contexts

✅ Good — context handles the job:

defmodule MyApp.Accounts do
  def register_user(attrs) do
    with {:ok, user} <- create_user(attrs) do
      MyApp.Workers.SendWelcomeEmail.new(%{user_id: user.id})
      |> Oban.insert()

      {:ok, user}
    end
  end
end

❌ Bad — LiveView enqueues directly:

def handle_event("register", params, socket) do
  MyApp.Workers.SendWelcomeEmail.new(%{user_id: user.id}) |> Oban.insert()
end

Return Values

Return exactly one of these from perform/1. Use {:error, reason} for retryable failures; never raise.

@impl Oban.Worker
def perform(%Oban.Job{args: args}) do
  # Success — job completed, marked as completed
  {:ok, result}

  # Retryable failure — will retry up to max_attempts
  {:error, reason}

  # Permanent failure — will NOT retry, marked as cancelled
  {:cancel, reason}

  # Snooze — reschedule for later (in seconds)
  {:snooze, 60}
end

Queue Configuration

# config/config.exs
config :my_app, Oban,
  repo: MyApp.Repo,
  queues: [
    default: 10,      # 10 concurrent jobs
    mailers: 5,       # 5 concurrent email jobs
    imports: 2         # 2 concurrent import jobs (resource-heavy)
  ]

# config/test.exs — use testing mode
config :my_app, Oban,
  testing: :inline    # Jobs execute immediately in the test process

Idempotency

❌ Bad — sends duplicate emails on retry:

@impl Oban.Worker
def perform(%Oban.Job{args: %{"user_id" => user_id}}) do
  user = MyApp.Accounts.get_user!(user_id)
  MyApp.Mailer.send_welcome(user)
  {:ok, :sent}
end

✅ Good — check if already processed:

@impl Oban.Worker
def perform(%Oban.Job{args: %{"user_id" => user_id}}) do
  user = MyApp.Accounts.get_user!(user_id)

  if user.welcome_email_sent_at do
    {:ok, :already_sent}
  else
    with {:ok, _} <- MyApp.Mailer.send_welcome(user),
         {:ok, _} <- MyApp.Accounts.mark_welcome_sent(user) do
      {:ok, :sent}
    end
  end
end

Unique Jobs

use Oban.Worker,
  queue: :default,
  unique: [
    period: 300,              # 5-minute uniqueness window
    fields: [:args, :queue],  # match on these fields
    keys: [:user_id],         # only compare these arg keys
    states: [:available, :scheduled, :executing]
  ]

Scheduled and Recurring Jobs

# Schedule a job for later
%{report_id: report.id}
|> MyApp.Workers.GenerateReport.new(schedule_in: {1, :hour})
|> Oban.insert()

# Cron-based recurring jobs (in config)
config :my_app, Oban,
  repo: MyApp.Repo,
  queues: [default: 10],
  plugins: [
    {Oban.Plugins.Cron, crontab: [
      {"0 2 * * *", MyApp.Workers.NightlyCleanup},
      {"*/15 * * * *", MyApp.Workers.SyncData, args: %{source: "api"}}
    ]}
  ]

Testing

  • Use perform_job/2 — not perform/1. perform_job validates args and simulates the Oban runtime.
  • Use assert_enqueued/1 — verify jobs were enqueued with correct args.
  • Use Oban.Testing inline mode in test config — jobs run synchronously in the test process.
  • Test all return paths — success, retryable error, and cancel.
defmodule MyApp.Workers.SendWelcomeEmailTest do
  use MyApp.DataCase, async: true
  use Oban.Testing, repo: MyApp.Repo

  alias MyApp.Workers.SendWelcomeEmail

  test "enqueuing a welcome email job" do
    user = user_fixture()

    SendWelcomeEmail.new(%{user_id: user.id})
    |> Oban.insert()

    assert_enqueued(worker: SendWelcomeEmail, args: %{user_id: user.id})
  end

  test "performing the job sends the email" do
    user = user_fixture()

    assert {:ok, :sent} =
      perform_job(SendWelcomeEmail, %{user_id: user.id})
  end

  test "cancels if user not found" do
    assert {:cancel, _reason} =
      perform_job(SendWelcomeEmail, %{user_id: -1})
  end
end

Job Args Best Practices

❌ Bad — large data in args (stored as JSON in database):

SendReport.new(%{
  user_id: user.id,
  report_data: large_data_structure  # Don't do this!
})

✅ Good — store IDs, fetch fresh data in worker:

SendReport.new(%{user_id: user.id, report_id: report.id})

skills

infrastructure

oban-essentials

SKILL.md

README.md

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