How to Use Rsync for Zero-Downtime Server Migrations

The Terrible Way to Migrate

When most beginners move a 50GB website to a new server, they use an FTP client (like FileZilla) to download the 50GB to their home computer, and then upload it to the new server.

• It takes hours.
• Connections randomly drop.
• Linux file permissions get annihilated.

Enter Rsync

rsync transfers files directly between the two servers at their maximum network pipe speed (often 1 Gbps to 10 Gbps). Better yet, if the transfer is interrupted, rsync resumes exactly where it left off.

Step 1: The Basic Transfer

Assume you are logged into your OLD Server (Source). You want to send the folder /var/www/mywebsite to your NEW Server (Destination) at IP 203.0.113.50.

Run this command on the old server:

rsync -avz /var/www/mywebsite root@203.0.113.50:/var/www/

Understanding the Flags (-avz):

• -a (Archive): Preserves all permissions, symlinks, and ownerships perfectly.
• -v (Verbose): Shows you a scrolling list of what is currently being transferred.
• -z (Compress): Compresses file data during the transfer to save bandwidth.

(It will ask for the root password of the new server before beginning).

Step 2: The Two-Pass Zero Downtime Strategy

If you have a massive WooCommerce store, you can't put it in maintenance mode for 4 hours while rsync transfers 200GB of images. Here is the professional strategy:

1. Pass 1 (While live): Run the rsync command normally. The site stays online. It takes 4 hours, but users are still buying products on the old server.
2. Database Migration: Put the site in maintenance mode. Export the database and import it to the new server (Takes 2 minutes).
3. Pass 2 (The Delta Transfer): Run the exact same rsync command again. Because Rsync is smart, it compares the folders and only transfers the 5 new images uploaded in the last 4 hours. It finishes in 30 seconds.
4. Update DNS: Point your domain to the new server.

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Custom SSH Ports

If your new server has a secure, custom SSH port (e.g., 2222), you must specify it using the -e flag:

rsync -avz -e 'ssh -p 2222' /var/www/mywebsite root@203.0.113.50:/var/www/

The Trailing Slash Rule Warning

Rsync treats /folder and /folder/ wildly differently.

• rsync /var/www will create a new folder called "www" inside the destination.
• rsync /var/www/ will dump the contents of "www" into the destination. Always double-check your trailing slashes!

FAQs

Q: Does rsync delete files on the destination if they were deleted on the source?
A: Not by default. If you want a perfect mirror that deletes old files on the new server, you must add the --delete flag. Use this with extreme caution.