Requirements

TYPO3 version

Composer packages for TYPO3 can be found on packagist.org down to version 6.2.0: typo3/cms-*.

Composer

Composer is a program that is written in PHP. Instructions for downloading and installing Composer can be found on getcomposer.org.

Your host needs to be able to execute the composer binary.

Folder structure

If the root folder of your project is identical to your web root folder, you need to change this. Composer will add a vendor/ folder to your project root, and if your project root and your web root are identical, this can be a security issue: files in the vendor/ folder could be directly accessible via HTTP request.

Bad:

$ tree typo3_root
├── index.php
├── fileadmin/
├── typo3/
├── typo3conf/
└── typo3temp/

You will need a web root folder in your project. You can find many tutorials with different names for your web root folder (e.g. www/, htdocs/, httpdocs/, wwwroot/, html/). The truth is: the name does not matter because we can configure it in the settings in a later step. We will use public/ in our example.

Bad:

$ tree typo3_root
└── cms/ (web root)
    └── public/
        ├── index.php
        ├── fileadmin/
        ├── typo3/
        ├── typo3conf/
        └── typo3temp/

Here you would access the installation via https://example.com/cms/public/index.php, which would also be a security issue as any other directory outside of the dedicated project root directory could be accessible.

Also having a directory structure like that can create file and directory resolving issues within the TYPO3 backend.

Good:

$ tree typo3_root
└── public/
    ├── index.php
    ├── fileadmin/
    ├── typo3/
    ├── typo3conf/
    └── typo3temp/

If you do not have such a web root directory, you will have to refactor your project before proceeding. First, you create the new directory public/ and basically move everything you have inside that subdirectory. Then check all of your custom code for path references that need to be adjusted to add the extra public/ part inside of it. Usually, HTTP(S) links are relative to your root, so only absolute path references may need to be changed (e.g. cronjobs, CLI references, configuration files, .gitignore, ...).

Please be aware that you very likely need to tell your web server about the changed web root folder if necessary. You do that by changing a DocumentRoot (Apache) or root (Nginx) configuration option. Most hosting providers offer a user interface to change the base directory of your project.

For local development with DDEV or Docker <https://docker.com> you will also need to adjust the corresponding configuration files.

Git version control, local development and deployment

This migration guide expects that you are working locally with your project and use Git version control for it.

If you previously used the TYPO3 Legacy installation (from a release ZIP) and did not yet use Git versioning, this is a good time to learn about version control first.

All operations should ideally take place in a separate branch of your Git repository. Only when everything is completed you should move your project files to your staging/production instance (usually via deployment, or via direct file upload to your site). If you do not yet use deployment techniques, this is a good time to learn about that.

Composer goes hand in hand with a good version control setup and a deployment workflow. The initial effort to learn about all of this is well worth your time, it will make any project much smoother and more maintainable.

Local development platforms like DDEV, Docker or XAMPP/WAMPP/MAMPP allow you to easily test and maintain TYPO3 projects, based on these git, docker and composer concepts.

Of course you can still perform the Composer migration on your live site without version control and without deployment, but during the migration your site will not be accessible, and if you face any problems, you may not be able to easily revert to the initial state.

Code integrity

Your project must have the TYPO3 Core and all installed extensions in their original state. If you applied manual changes to the files, these will be lost during the migration steps.