Setting up a local domain name on OSX can streamline your development process by allowing you to access your Docker containers or other services via a custom, easy-to-remember URL. This is particularly useful for multisite applications, as it lets you choose a custom domain for every site for local development. It's also possible to add several custom domain names for 127.0.0.1.

Step 1: Open Your Terminal

Launch the Terminal application from your Applications folder or use Spotlight Search.

Step 2: Edit the Hosts File

1. Open the Hosts File: Use the following command to open the hosts file in a text editor. This file maps domain names to IP addresses.

    sudo vim /etc/hosts
   

   The sudo command is necessary because the hosts file is a system file, and editing it requires administrative privileges. You'll be prompted to enter your password.

2. Add Your Custom Domain: Add new lines in the hosts file with the desired local domain names and the IP address of your service. For instance, to map myapp.local and mysite.local to 127.0.0.1:

    127.0.0.1 myapp.local
    127.0.0.1 mysite.local
   

   In vim, press i to enter insert mode, add the lines, then press Esc to exit insert mode. Type :wq and press Enter to save and exit.

   Adding these entries tells your computer to resolve myapp.local and mysite.local to 127.0.0.1, which is the loopback address pointing to your local machine. This is useful for accessing locally hosted services or Docker containers via a custom URL.

Step 3: Save and Exit

1. Save Changes: In vim, after adding your custom domain entries, press Esc to exit insert mode. Then type :wq and press Enter to save and close the file.

2. Flush DNS Cache: Ensure your changes take effect by flushing the DNS cache. This clears any cached DNS records and forces the system to read the updated hosts file.

    sudo dscacheutil -flushcache
   

   Flushing the DNS cache is crucial to ensure that your changes to the hosts file are recognized by your system immediately.

Step 4: Configure Docker Container (if using Docker)

1. Run Your Docker Container: Make sure your Docker container is running. For example, to run an NGINX server, use the following command:

    docker run -it --rm -d -p 80:80 --name my-nginx nginx
   

   This command starts an NGINX container, mapping port 80 of the container to port 80 of your local machine. The --rm flag ensures the container is removed after it stops, and -d runs the container in detached mode.

2. Access via Custom Domain: You should now be able to access your Docker container using the custom domain names, e.g., http://myapp.local and http://mysite.local. Open a web browser and navigate to these URLs to verify that your container is accessible via the custom domains.

Happy coding!