Product Perfect

Elixir Supervisors is a programming language feature that provides fault-tolerance capabilities, designed to handle errors and ensure system recovery. It was introduced as part of the Elixir programming language, which was first released in 2011 by José Valim. The Supervisor module in Elixir allows developers to build applications with self-healing properties by automatically restarting child processes when they fail. This robust error handling mechanism is derived from Erlang's OTP (Open Telecom Platform) framework, upon which Elixir is built. As such, it embodies the philosophy of "let it crash" for building resilient systems that can recover from failures autonomously.

Ask the right questions secure the right Elixir Supervisors talent among an increasingly shrinking pool of talent.

First 20 minutes

General Elixir Supervisors app knowledge and experience

The first 20 minutes of the interview should seek to understand the candidate's general background in Elixir Supervisors application development, including their experience with various programming languages, databases, and their approach to designing scalable and maintainable systems.

What is the primary function of a Supervisor in Elixir?

The primary function of a Supervisor in Elixir is to monitor its child processes and restart them when they fail, ensuring the application's resilience.

How would you define a simple Supervisor in Elixir?

A simple Supervisor in Elixir can be defined using the Supervisor module and specifying the child processes in the start_link function. For example: Supervisor.start_link(children, strategy: :one_for_one).

What are the different types of supervision strategies available in Elixir?

Elixir provides four supervision strategies: :one_for_one, :one_for_all, :rest_for_one, and :simple_one_for_one.

Describe the difference between :one_for_one and :one_for_all supervision strategies.

:one_for_one only restarts the failed child process, whereas :one_for_all restarts all child processes when one of them fails.

How would you dynamically add a child to a running Supervisor in Elixir?

You can dynamically add a child to a running Supervisor using the Supervisor.start_child function, passing the Supervisor's PID and the child specification.

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What you’re looking for early on

Has the candidate demonstrated a solid understanding of Elixir Supervisors?

Did the candidate show the ability to write clean, efficient Elixir code?

Did they exhibit knowledge of OTP (Open Telecom Platform) principles?

Could the candidate explain how to handle different types of failures in an Elixir system?

Next 20 minutes

Specific Elixir Supervisors development questions

The next 20 minutes of the interview should focus on the candidate's expertise with specific backend frameworks, their understanding of RESTful APIs, and their experience in handling data storage and retrieval efficiently.

What are the main components of a child specification in Elixir?

A child specification in Elixir includes the module, args, restart, shutdown, type, and id.

Describe the difference between :permanent, :temporary, and :transient restart values in a child specification.

:permanent restarts the child process whenever it terminates, :temporary never restarts it, and :transient only restarts it if it terminates abnormally.

How would you remove a child process from a Supervisor in Elixir?

You can remove a child process from a Supervisor using the Supervisor.terminate_child function, followed by Supervisor.delete_child.

What is the purpose of the init/1 callback function in a Supervisor?

The init/1 callback function in a Supervisor is used to define the child processes and the supervision strategy.

How would you handle a situation where a child process needs to be restarted in a specific order?

In such a situation, you would use the :rest_for_one supervision strategy, which restarts the failed process and any process started after it.

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At this point, a skilled Elixir Supervisors engineer should demonstrate strong problem-solving abilities, proficiency in Elixir Supervisors programming language, and knowledge of software development methodologies. Red flags include lack of hands-on experience, inability to articulate complex concepts, or unfamiliarity with standard coding practices.

Digging deeper

Code questions

These will help you see the candidate's real-world development capabilities with Elixir Supervisors.

What does the following Elixir code do?
defmodule MySupervisor do
  use Supervisor
  def start_link do
    Supervisor.start_link(__MODULE__, :ok)
  end
  def init(:ok) do
    children = []
    Supervisor.init(children, strategy: :one_for_one)
  end
end
This code defines a Supervisor in Elixir. The Supervisor is started with the start_link function. It uses the one_for_one strategy, which means if a child process dies, only that process is restarted.
What will be the output of the following Elixir code?
IO.puts "Hello, " <> "World!"
The output of this code will be 'Hello, World!'. The <> operator is used for concatenation of strings in Elixir.
What does this Elixir code do?
list = [1, 2, 3, 4]
Enum.map(list, fn x -> x * 2 end)
This code takes a list of integers and uses the Enum.map function to create a new list where each element is multiplied by 2. The output would be [2, 4, 6, 8].
What does this Elixir code do?
Task.async(fn -> 1 + 2 end)
|> Task.await()
This code creates a new process that adds 1 and 2 together using the Task.async function. Task.await is then used to wait for the process to finish and return its result. The output would be 3.

Wrap-up questions

Final candidate for Elixir Supervisors Developer role questions

The final few questions should evaluate the candidate's teamwork, communication, and problem-solving skills. Additionally, assess their knowledge of microservices architecture, serverless computing, and how they handle Elixir Supervisors application deployments. Inquire about their experience in handling system failures and their approach to debugging and troubleshooting.

What is the role of the :simple_one_for_one supervision strategy?

The :simple_one_for_one supervision strategy is used when you need to dynamically manage a set of similar child processes.

How would you implement a back-off strategy for restarting child processes in Elixir?

To implement a back-off strategy, you would use the :restart intensity and :period options in the Supervisor specification.

What are the limitations of a Supervisor in Elixir?

Supervisors in Elixir cannot manage the state of child processes, and they cannot handle dependencies between child processes unless they are started in a specific order.

Elixir Supervisors application related

Product Perfect's Elixir Supervisors development capabilities

Beyond hiring for your Elixir Supervisors engineering team, you may be in the market for additional help. Product Perfect provides seasoned expertise in Elixir Supervisors projects, and can engage in multiple capacities.

Elixir Supervisors Consultive assessments

Elixir Supervisors Application Conversion Assessment Elixir Supervisors Application Integration Assessment Elixir Supervisors Data & Database Integration Assessment

Custom Elixir Supervisors development projects

Custom Elixir Supervisors App Conversion Elixir Supervisors Custom App Development Process App UI Design for Elixir Supervisors Facelifts

Hiring guide for Elixir Supervisors Engineers

Elixir Supervisors Developer Hiring Guide

What you’re looking for early on

The ideal back-end app developer

What you’re looking to see on the Elixir Supervisors engineer at this point.

Elixir Supervisors Consultive assessments

Custom Elixir Supervisors development projects