Move docker with the least downtime possible

move_docker.sh

#!/bin/bash

# Check if a command line argument is provided
if [ -z "$1" ]
then
    # If not, prompt the user to enter the target directory
    echo "Please enter the target directory:"
    read -r target_dir
else
    # If an argument is provided, use it as the target directory
    target_dir=$1
fi

# Calculate used space in /var/lib/docker (in KB)
used_space=$(du -sk /var/lib/docker | cut -f1)

# Calculate available space in the target directory (in KB)
available_space=$(df -k "$target_dir" | tail -1 | awk '{print $4}')

# Check if there's enough available space on the target disk
if (( available_space < used_space )); then
    echo "Not enough space on the target disk"
    exit 1
fi

echo 'Enough space on the target disk, running initial sync'
# First run sync to do most of the copying while the service is running
rsync -az --info=progress2 /var/lib/docker "$target_dir"


# Stop docker
systemctl stop docker

# Catch up the last few changes
echo 'Stopping docker, running final sync'
rsync -az --info=progress2 /var/lib/docker "$target_dir"

echo 'Final sync complete, restarting docker with new data directory'
# Create a new docker.service file with -g /data1/docker added to the ExecStart line
cp /lib/systemd/system/docker.service /tmp/docker.service
sed -i "s|^ExecStart=/usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock$|& -g $target_dir|g" /tmp/docker.service

# Move over the prepared directory with -g /data1/docker added to the ExecStart line
cp /tmp/docker.service /lib/systemd/system/docker.service

# Reload systemd, enable and start the service
systemctl daemon-reload

# Start docker
systemctl start docker

echo 'Docker restarted - once you have confirmed everything is working, you can delete the old data directory /var/lib/docker'