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πŸ’¬ A Step-by-Step Beginners Tutorial for Building, Testing & Deploying a Chat app in Phoenix 1.4.4 (latest)! πŸš€
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Phoenix Chat Example


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A step-by-step tutorial for building, testing and deploying a Chat app in Phoenix!


Chat apps are the "Hello World" of "real time" example apps.

Most example apps show a few basics and then ignore "the rest" ...
So "beginners" are often left "lost" or "confused" as to what they should do or learn next!
Very few tutorials consider Testing, Deployment, Documentation or other "Enhancements" which are all part of the "Real World" of building and running apps; so those are topics we will cover to "fill in the gaps".

We wrote this tutorial to be easiest way to learn Phoenix, Ecto and "Channels" with a practical example anyone can follow.


A simple step-by-step tutorial showing you how to:

  • Create a Phoenix App from scratch (using the mix chat "generator" command)
  • Add a "Channel" so your app can communicate over "WebSockets".
  • Implement a basic "front-end" in "plain" JavaScript (ES5 without any libraries) to interact with Phoenix (send/receive messages via WebSockets)
  • Add a simple "Ecto" schema to define the Database Table (to store messages)
  • Write the functions ("CRUD") to save message/sender data to a database table.
  • Test that everything is working as expected.
  • Deploy to Heroku so you can show people your creation!

Initially, we deliberately skip over configuration files and "Phoenix Internals" because you (beginners) don't need to know about them to get started. But don't worry, we will return to them when needed. We favour "just-in-time" (when you need it) learning as it's immediately obvious and practical why we are learning something.


This example is for complete beginners as a "My First Phoenix" App.

We try to assume as little as possible, but if you think we "skipped a step" or you feel "stuck" for any reason, or have any questions (related to this example), please open an issue on GitHub!
Both the @dwyl and Phoenix communities are super beginner-friendly, so don't be afraid/shy.
Also, by asking questions, you are helping everyone that is or might be stuck with the same thing!


These instructions show you how to create the Chat app from scratch.

0. Pre-requisites (Before you Start)

  1. Elixir Installed on your local machine.
brew install elixir

Note: if you already have Elixir installed on your Mac, and just want to upgrade to the latest version, run: brew upgrade elixir

  1. Phoenix framework installed. see:
mix archive.install hex phx_new 1.4.4
  1. PostgreSQL (Database Server) installed (to save chat messages)
  1. Basic Elixir Syntax knowledge will help,
    please see:

  2. Basic JavaScript knowledge is advantageous (but not essential as the "front-end" code is quite basic and well-commented). see:

Check You Have Everything Before Starting

Check you have the latest version of Elixir (run the following command in your terminal):

elixir -v

You should see something like:

Erlang/OTP 21 [erts-10.3.4] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [hipe] [dtrace]

Elixir 1.8.1 (compiled with Erlang/OTP 21)

Check you have the latest version of Phoenix:

mix -v

You should see:

Phoenix v1.4.4

Confirm PostgreSQL is running (so the App can store chat messages) run the following command:

lsof -i :5432

You should see output similar to the following:

postgres 529 Nelson  5u  IPv6 0xbc5d729e529f062b      0t0  TCP localhost:postgresql (LISTEN)
postgres 529 Nelson  6u  IPv4 0xbc5d729e55a89a13      0t0  TCP localhost:postgresql (LISTEN)

This tells us that PostgreSQL is "listening" on TCP Port 5432 (the default port)

With all those "pre-flight checks" performed, let's get going!

1. Create The App

In your terminal program on your localhost, type the following command to create the app:

mix chat

That will create the directory structure and project files.

When asked to "Fetch and install dependencies? [Yn]",
Type y (the "Y" key) in your terminal, followed by the [Enter] / [Return] key.

You should see:

Change directory into the chat directory by running the suggested command:

cd chat

Note: at this point there is already an "App" it just does not do anything (yet) ...
you can run mix phx.server in your terminal
and open http://localhost:4000 in your browser
and you will see is the default "Welcome to Phoenix" homepage:


Let's continue to the interesting part!

2. Create the (WebSocket) "Channel"

Generate the (WebSocket) channel to be used in the chat app:

mix Room

If you are prompted to confirm installation, type y and hit the [Enter] key.

This will create two files:

* creating lib/chat_web/channels/room_channel.ex
* creating test/chat_web/channels/room_channel_test.exs

The room_channel.ex file handles receiving/sending messages and the room_channel_test.exs tests basic interaction with the channel. (Don't worry about this yet, we will look at the test file in step 14 below!)

We are informed that we need to update a piece of code into your app:

Add the channel to your `/lib/chat_web/channels/user_socket.ex` handler, for example:

    channel "room:lobby", ChatWeb.RoomChannel

Open the file called /lib/chat_web/channels/user_socket.ex
and change the line:

# channel "room:*", ChatWeb.RoomChannel


channel "room:lobby", ChatWeb.RoomChannel

Example: user_socket.ex#L5

For more detail on Phoenix Channels, (we highly recommend you) read:

3. Update the Template File (UI)

Open the the /lib/chat_web/templates/page/index.html.eex file
and copy-paste (or type) the following code:

<!-- The list of messages will appear here: -->
<ul id='msg-list' class='row' style='list-style: none; min-height:200px; padding: 10px;'></ul>

<div class="row">
  <div class="col-xs-3">
    <input type="text" id="name" class="form-control" placeholder="Your Name" autofocus>
  <div class="col-xs-9">
    <input type="text" id="msg" class="form-control" placeholder="Your Message">

This is the basic form we will use to input Chat messages.
The classes e.g: "form-control" and "col-xs-3" are Bootstrap CSS classes to style the form.
Phoenix includes Bootstrap by default so you can get up-and-running with your App/Idea/"MVP"!
If you are unfamiliar with Bootstrap UI, read:
and if you specifically want to understand the Bootstrap forms, see:

Your index.html.eex template file should look like this: /lib/chat_web/templates/page/index.html.eex (snapshot)

4. Update the "Client" code in App.js

Open: /assets/js/app.js and uncomment the line:

import socket from "./socket"

with the line uncommented our app will import the socket.js file which will give us WebSocket functionality.

Then add the following JavaScript ("Client") code:

let channel ='room:lobby', {}); // connect to chat "room"

channel.on('shout', function (payload) { // listen to the 'shout' event
  let li = document.createElement("li"); // create new list item DOM element
  let name = || 'guest';    // get name from payload or set default
  li.innerHTML = '<b>' + name + '</b>: ' + payload.message; // set li contents
  ul.appendChild(li);                    // append to list

channel.join(); // join the channel.

let ul = document.getElementById('msg-list');        // list of messages.
let name = document.getElementById('name');          // name of message sender
let msg = document.getElementById('msg');            // message input field

// "listen" for the [Enter] keypress event to send a message:
msg.addEventListener('keypress', function (event) {
  if (event.keyCode == 13 && msg.value.length > 0) { // don't sent empty msg.
    channel.push('shout', { // send the message to the server on "shout" channel
      name: name.value,     // get value of "name" of person sending the message
      message: msg.value    // get message text (value) from msg input field.
    msg.value = '';         // reset the message input field for next message.

Take a moment to read the JavaScript code and confirm your understanding of what it's doing.
Hopefully the in-line comments are self-explanatory, but if anything is unclear, please ask!

At this point your app.js file should look like this: /assets/js/app.js

5. Install the Node.js Dependencies

In order to use JS in your Phoenix project, you need to install the node.js dependencies:

cd assets && npm install && cd ..

That might take a few seconds (depending on your internet connection speed)

But once it completes you should see:

added 1022 packages from 600 contributors and audited 14893 packages in 32.079s
found 0 vulnerabilities

Storing Chat Message Data/History

If we didn't want to save the chat history, we could just deploy this App immediately and we'd be done!

6. Create/Configure Database

Create the database to store the chat history data:

mix ecto.create

You should see:

The database for Chat.Repo has been created

7. Generate Database Schema to Store Chat History

Run the following command in your terminal:

mix phx.gen.schema Message messages name:string message:string

You should see the following output:

* creating lib/chat/message.ex
* creating priv/repo/migrations/20180107074333_create_messages.exs

Remember to update your repository by running migrations:

    $ mix ecto.migrate

Let's break down that command for clarity:

  • mix phx.gen.schema - the mix command to create a new schema (database table)
  • Message - the singular name for record in our messages "collection"
  • messages - the name of the collection (or database table)
  • name:string - the name of the person sending a message, stored as a string.
  • message:string - the message sent by the person, also stored as a string.

The creating lib/chat/message.ex file is the "schema" for our Message database table.

Additionally a migration file is created, e.g: creating priv/repo/migrations/20180107074333_create_messages.exs The "migration" actually creates the database table in our database.

8. Run the Ecto Migration (Create The Database Table)

In your terminal run the following command to create the messages table:

mix ecto.migrate

You should see the following in your terminal:

Compiling 1 file (.ex)
Generated chat app
[info] == Running Chat.Repo.Migrations.CreateMessages.change/0 forward
[info] create table messages
[info] == Migrated in 0.0s

8.1 Review the Messages Table Schema

If you open your PostgreSQL GUI (e.g: pgadmin) you will see that the messages table has been created in the chat_dev database:


You can view the table schema by "right-clicking" (ctrl + click on Mac) on the messages table and selecting "properties":


9. Insert Messages into Database

Open the lib/chat_web/channels/room_channel.ex file and inside the function def handle_in("shout", payload, socket) do add the following line:

Chat.Message.changeset(%Chat.Message{}, payload) |> Chat.Repo.insert  

So that your function ends up looking like this:

def handle_in("shout", payload, socket) do
  Chat.Message.changeset(%Chat.Message{}, payload) |> Chat.Repo.insert  
  broadcast socket, "shout", payload
  {:noreply, socket}

10. Load Existing Messages (When Someone Joins the Chat)

Open the lib/chat/message.ex file and add a new function to it:

def get_messages(limit \\ 20) do
  Chat.Repo.all(Chat.Message, limit: limit)

This function accepts a single parameter limit to only return a fixed/maximum number of records. It uses Ecto's all function to fetch all records from the database. Message is the name of the schema/table we want to get records for, and limit is the maximum number of records to fetch.

11. Send Existing Messages to the Client when they Join

In the /lib/chat_web/channels/room_channel.ex file create a new function:

def handle_info(:after_join, socket) do
  |> Enum.each(fn msg -> push(socket, "shout", %{
      message: msg.message,
    }) end)
  {:noreply, socket} # :noreply

and at the top of the file update the join function to the following:

def join("room:lobby", payload, socket) do
  if authorized?(payload) do
    send(self(), :after_join)
    {:ok, socket}
    {:error, %{reason: "unauthorized"}}

12. Checkpoint: Our Chat App Saves Messages!! (Try it!)

Start the Phoenix server (if it is not already running):

mix phx.server

Note: it will take a few seconds to compile but then you should see:


The line:

[info] Running ChatWeb.Endpoint with Cowboy using

tells us that our code compiled (as expected) and the Chat App is running on TCP Port 4000!

Open the Chat web app in two separate browser windows: http://localhost:4000
(if your machine only has one browser try using one "incognito" tab)

You should be able to send messages between the two browser windows:

Congratulations! You have a working (basic) Chat App written in Phoenix!

The chat (message) history is saved!

This means you can refresh the browser or join in a different browser and you will still see the history!

Testing our App (Automated Testing)

Automated testing is one of the best ways to ensure reliability in your web applications.

Note: If you are completely new to Automated Testing or "Test Driven Development" ("TDD"), we recommend reading/following the "basic" tutorial:

Testing in Phoenix is fast (tests run in parallel!) and easy to get started! The ExUnit testing framework is built-in so there aren't an "decisions/debates" about which framework or style to use.

If you have never seen or written a test with ExUnit, don't fear, the syntax should be familiar if you have written any sort of automated test in the past.

13. Run the Default/Generated Tests

Whenever you create a new Phoenix app or add a new feature (like a channel), Phoenix generates a new test for you.

We run the tests using the mix test command:


In this case one of the tests fails. (7 tests, 1 failure)

The "stacktrace" informs us that location of the failing test is: test/chat_web/controllers/page_controller_test.exs:4 And that the "assertion" is:

assert html_response(conn, 200) =~ "Welcome to Phoenix!"

In English this means we are asserting that the "homepage" returns an "HTML response" which contains the words: "Welcome to Phoenix!"

Since we changed the code in /lib/chat_web/templates/page/index.html.eex (in section 3, above), the page no longer contains the string " Welcome to Phoenix! ".

13.1 Fix The Failing Test

We have two options:

  1. Add the text "Welcome to Phoenix!" back into page/index.html.eex
  2. Update the assertion to something that is on the page e.g: "msg-list".

Both are valid approaches, however we prefer the second option because it "reflects the reality" rather than "altering reality" to match the exiting assertion.
Let's make the update now. Open the test/chat_web/controllers/page_controller_test.exs file and change line 6 to:

assert html_response(conn, 200) =~ "msg-list"

We know that "msg-list" is on the page because that's the id of the <ul> where our message history is bing displayed.

Your page_controller_test.exs file should now look like this: /test/chat_web/controllers/page_controller_test.exs#L6

13.2 Re-Run The Test(s)

Now that we have updated the assertion, we can re-run the tests with the mix test command:


14. Understanding The Channel Tests

It's worth taking a moment (or as long as you need!) to understand what is going on in the /room_channel_test.exs file. Open it if you have not already, read the test descriptions & code.

For a bit of context we recommend reading:

14.1 Analyse a Test

Let's take a look at the first test in /test/chat_web/channels/room_channel_test.exs#L14-L17:

test "ping replies with status ok", %{socket: socket} do
  ref = push socket, "ping", %{"hello" => "there"}
  assert_reply ref, :ok, %{"hello" => "there"}

The test get's the socket from the setup function (on line 6 of the file) and assigns the result of calling the push function to a variable ref push merely pushes a message (the map %{"hello" => "there"}) on the socket to the "ping" topic.

The handle_in function clause which handles the "ping" topic:

def handle_in("ping", payload, socket) do
  {:reply, {:ok, payload}, socket}

Simply replies with the payload you send it, therefore in our test we can use the assert_reply Macro to assert that the ref is equal to :ok, %{"hello" => "there"}

Note: if you have questions or need any help understanding the other tests, please open an issue on GitHub we are happy to expand this further!
(we are just trying to keep this tutorial reasonably "brief" so beginners are not "overwhelmed" by anything...)

15. What is Not Tested?

Often we can learn a lot about an application (or API) from reading the tests and seeing where the "gaps" in testing are.

Thankfully we can achieve this with only a couple of steps:

15.1 Add excoveralls as a (Development) Dependency to mix.exs

Open your mix.exs file and find the "deps" function:

defp deps do

Add the following line to the end of the List:

{:excoveralls, "~> 0.7.0", only: [:test, :dev]}, # tracking test coverage

Additionally, find the def project do section (towards the top of mix.exs) and add the following lines to the List:

test_coverage: [tool: ExCoveralls],
preferred_cli_env: ["coveralls": :test, "coveralls.detail": :test,
  "": :test, "coveralls.html": :test]

Then, install the dependency on excoveralls we just added to mix.exs:

mix deps.get

You should see:

Resolving Hex dependencies...
Dependency resolution completed:
* Getting excoveralls (Hex package)
... etc.

15.2 Create a New File Called coveralls.json

In the "root" (base directory) of the Chat project, create a new file called coveralls.json and copy-paste the following:

  "coverage_options": {
    "minimum_coverage": 100
  "skip_files": [

This file is quite basic, it instructs the coveralls app to require a minimum_coverage of 100% (i.e. everything is tested1) and to ignore the files in the test/ directory for coverage checking.

1We believe that investing a little time up-front to write tests for all our code is worth it to have fewer bugs later.
Bugs are expensive, tests are cheap and confidence/reliability is priceless

15.3 Run the Tests with Coverage Checking

To run the tests with coverage, copy-paste the following command into your terminal:

MIX_ENV=test mix do coveralls.json

You should see:

As we can se here, only 59.3% of lines of code in /lib are being "covered" by the tests we have written.

To view the coverage in a web browser run the following:

MIX_ENV=test mix coveralls.html && open cover/excoveralls.html

This will open the Coverage Report (HTML) in your default Web Browser:

coverage-report-59 3-percent

Note: you will need to temporarily lower the coverage threshold in coveralls.json form 100 to 50 for this command to work because it's expecting 100% coverage.

Continuous Integration

Continuous integration lets you automate running the tests to check/confirm that your app is working as expected (before deploying). This prevents accidentally "breaking" your app.

Thankfully the steps are quite simple.

If you are new to Continuous Integration, or need a refresher, we wrote a step-by-step tutorial for it! see:

The Elixir-specific section is:

We only need to add .travis.yml file to the project with the following lines:

language: elixir
elixir: # Latest version of Elixir
  - 1.6
addons: # ensure that Travis-CI provisions a DB for our test:
  postgresql: '9.5'
  - MIX_ENV=test
script: # run the tests:
  - mix test

You will need to enable your project on Travis-CI for the build to run.
Please see:


Deployment to Heroku takes a few minutes, but has a few "steps", therefore we have created a separate guide for it:

Once you have deployed you will will be able to view/use your app in any Web/Mobile Browser.



Want more? Ask! Please share your thoughts on GitHub:


This repo is inspired by @chrismccord's Simple Chat Example:

At the time of writing Chris' example is still Phoenix 1.2 see: therefore we decided to write a quick version for Phoenix 1.4 :-)

Recommended Reading / Learning

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