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Introduction

To develop and host a Phoenix application on Square Cloud, it’s essential to follow a structured sequence of configurations and prerequisites. This technical guide will cover the entire process, from initial setup to production deployment.

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Prerequisites

  • Square Cloud Account: Register through the signup page using your email.
  • Active plan: Ensures dedicated resources and optimized performance for your application. Check our available plans and choose the most suitable for your needs.
This guide runs on the Elixir runtime.

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Create the project

You need Erlang/OTP and Elixir on your machine. If you don’t have them, follow the official Elixir installation guide. Install the Phoenix project generator and create a project:
--no-ecto creates a project without a database, the simplest setup to deploy. Drop it if you need Ecto, then see Environment variables for the database address. Start the development server:
Phoenix listens on http://localhost:4000 in development.

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Build for production

Square Cloud builds your app when it starts: before running your START command, it fetches your dependencies with mix deps.get. The START command below then compiles the app in production mode (MIX_ENV=prod), builds and digests the assets with mix assets.deploy, and starts the server. You don’t need to build anything on your machine, and your ZIP holds the project source.
The first start compiles your dependencies and downloads the asset tools (esbuild and Tailwind), so it takes a few minutes. Later starts reuse the compiled files.

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Port and host

Nothing to change: in production, the generated config/runtime.exs reads the PORT environment variable, which Square Cloud sets to 80, and listens on all network interfaces.

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Environment variables

Set these environment variables in the dashboard or with squarecloud app env set:

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Configure Square Cloud

Create a squarecloud.app file at the root of your project:
squarecloud.app
MAIN=mix.exs tells Square Cloud that the project runs on Elixir, and START replaces the default mix run --no-halt. mix phx.server starts the web server, so you don’t need PHX_SERVER. Projects with Ecto can apply migrations on every start by adding MIX_ENV=prod mix ecto.migrate && before mix phx.server.

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What goes in the ZIP

  • mix.exs and mix.lock.
  • config/, lib/, assets/, priv/ and the other source folders.
  • squarecloud.app.
Leave out _build/, which holds files compiled for your machine, and deps/: Square Cloud fetches the dependencies again and compiles everything on Linux.
Prefer a release? A release built on Windows or macOS does not run on Square Cloud, which runs Linux: build it on Linux, for example in WSL. Its start script is _build/prod/rel/my_app/bin/my_app, so the command is START=PHX_SERVER=true _build/prod/rel/my_app/bin/my_app start; PHX_SERVER=true makes the release start the web server. Keep mix.exs and mix.lock in the ZIP, because Square Cloud runs mix deps.get before START.

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Deploy and verify

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Via dashboard

1

Access the Upload Page

Access the upload page and upload your project zip file.
2

Configure Your Environment

After uploading your zip, you will need to configure the name, main file or runtime environment and other settings for your project.
If you are uploading a web project, make sure to select “Web Publication” and set a subdomain to your project.
3

Deploy Your Project

Finally, click on the “Deploy” button to host your project on Square Cloud.
After deployment, you can monitor your project’s status and logs from the dashboard.
Uploading application to Square Cloud
4

Confirm Your App Is Live

Your first deploy usually takes less than a minute. In the dashboard, wait for your application status to show as running and check the logs for any startup errors.
If you deployed a website or API, open https://<your-subdomain>.squareweb.app in your browser: you should see your application responding. If you deployed a bot, send it a command to confirm it is online.
App not starting? See the Troubleshooting guide for the most common causes and fixes.

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Via CLI

To use this method, your project needs a configuration file named squarecloud.app at its root. It tells Square Cloud how to run your application.

Configuration file guide

Learn how to create the squarecloud.app configuration file that defines your application’s environment.
1

Install the CLI

Install the Square Cloud CLI. If you already have it, run the same command to update it:
2

Log In

Run the command below. It opens your browser: approve the login there and the CLI is ready. There is no API key to copy. For scripts and CI, see CLI authentication.
3

Upload Your Project

From your project folder, run the command below. The CLI zips the current folder, leaving out what squarecloud.ignore lists, and uploads it:
To upload a zip you created yourself, pass it with --file:
4

Confirm Your App Is Live

Your first deploy usually takes less than a minute. Check your application status and logs directly from the terminal:
If you deployed a website or API, open https://<your-subdomain>.squareweb.app in your browser: you should see your application responding. If you deployed a bot, send it a command to confirm it is online.
App not starting? See the Troubleshooting guide for the most common causes and fixes.

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Common errors

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Custom Domain

To use a custom domain (e.g., mysite.com) instead of the default URL mysite.squareweb.app, you need the Standard plan or higher. The default URL comes from the SUBDOMAIN field in the configuration file. To connect your domain, follow how to set up your own domain.

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Minimum RAM Requirements

Minimum: 512MB RAM for websites and APIs, enough for a static build on the static runtime. For apps that render pages on a server (Next.js, Nuxt, Angular SSR and similar), we recommend at least 1GB RAM. For larger applications, allocate more RAM to prevent the application from running out of memory and crashing.

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Could not find this site.

Check if the subdomain/domain matches what’s configured in the SUBDOMAIN field or in the custom domain settings. If you just uploaded the site, wait up to 60 seconds for Square to enable first access.

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Site took too long to respond…

Your server must listen on port 80 and host 0.0.0.0. Square Cloud sets the PORT (80) and HOST (0.0.0.0) environment variables in your application: read them in your code instead of hardcoding other values. A server that listens only on localhost or 127.0.0.1 never receives requests.

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environment variable SECRET_KEY_BASE is missing

Set SECRET_KEY_BASE as shown in Environment variables, then restart the application.

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LiveView keeps reconnecting

PHX_HOST does not match the address in the browser. Set it to your subdomain or custom domain, then restart the application.

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Next steps

Environment variables

Keep secrets and settings out of your code and read them at runtime.

Custom domain

Serve your app on your own domain, on the Standard plan and above.

Troubleshooting

Fix an app that does not start or a site that does not respond.
For more about Phoenix, see the official Phoenix documentation and its release guide.

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Contact us

If you continue facing technical difficulties, our specialized support team is available to assist you. Contact us and we’ll be happy to help you resolve any issue: support quality is a big part of why developers rate Square Cloud 4.9/5 across 402 reviews on Google and Trustpilot.