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Bryan
Bryan

Posted on • Edited on • Originally published at devlogbook.com

2 Way Syncing between 2 Servers using lsyncd

Requirements

  1. At least 2 servers
  2. lsyncd installed on both servers
  3. ssh access between both servers

Assumptions

  1. username for both servers is: forge
  2. IP for server #1: 111.111.111
  3. IP for server #2: 222.222.222
  4. Folder to sync between the 2 servers (can be different, this example both same path and directory): syncro
  5. SSH key (can be different, this example same key name): syncro_key

Setup

This setup is for server #1, to setup server #2 it's the same. Just see the comments in the code in step #4

  1. Install lsyncd
    • sudo apt install lsyncd
  2. Create lsyncd log folder
    • sudo mkdir /var/log/lsyncd
  3. Create log and status files
    • sudo touch /var/log/lsyncd/lsyncd.{log,status}
  4. Create config file

    • sudo nano /etc/lsyncd.conf.lua
    • Note: Anything after -- are comments in the code
    -- server #1 setup
    settings {
          logfile = "/var/log/lsyncd/lsyncd.log", -- location of log file created in step 3
          statusFile = "/var/log/lsyncd/lsyncd.status", -- location of status file created in step 3
    }
    
    targetlist = {
        "forge@222.222.222:/home/forge/syncro", -- server #2 will have target forge@111.111.111
    }
    
    for _, server in ipairs( targetlist ) do
        sync {
            default.rsync,
            source = "/home/forge/syncro", -- folder which to sync from
            target = server,
            delete = 'running',
            rsync = {
                rsh = "ssh -i /home/forge/.ssh/syncro_key", -- ssh key
                update = true,
                archive = true,
                compress = true,
            }
        }
    end
    
  5. Start the lsyncd service

    • sudo service lsyncd start
  6. Set the config lsyncd service will use

    • sudo lsyncd /etc/lsyncd.conf.lua
    • IMPORTANT When the server restarts run this again

Notes

There is a limit to how many files/folders that can be watched

  • To check the current limit:
    • cat /proc/sys/fs/inotify/max_user_watches
  • To permanently alter the limit : (500000 is an example number)
    • sudo sysctl fs.inotify.max_user_watches=500000

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