Docu review done: Mon 03 Jul 2023 17:04:36 CEST

Table of Content

• General
• Installation
• Setup and initialize
• Conflict handling
• Resetting a csync2 cluster

General

csync2 is a bidirectional sync tool on file base

Installation

$ apt install csync2

Setup and initialize

First thing is, that you need an tuhentication key

$ csync2 -k /etc/csync2.key

For the transfer it selfe, you need to generate a ssl cert as well

$ openssl genrsa -out /etc/csync2_ssl_key.pem 2048
$ openssl req -batch -new -key /etc/csync2_ssl_key.pem -out /etc/csync2_ssl_cert.csr
$ openssl x509 -req -days 3600 -in /etc/csync2_ssl_cert.csr -signkey /etc/csync2_ssl_key.pem -out /etc/csync2_ssl_cert.pem

To configure csync2 a small config file /etc/csync2/csync2.cfg is needed, where you define the hosts, keys and so on

group mycluster
{
        host node1;
        host node2;

        key /etc/csync2.key;

        include /www/htdocs;
        exclude *~ .*;
}

Transfer config and certs/key to all the other nodes which are in your csync2 cluster and ensure that the service/socket is enabled and started.

$ sytstemctl enable --now csync2.socket

After the sockes are available everywhere, you can start the inintial sync.

$ csync2 -xv

Conflict handling

If csync2 detected changes during a sync by one or more hosts, you will get messages like this

While syncing file /etc/ssh/sshd_conf:
ERROR from peer site-2-host-1: File is also marked dirty here!
Finished with 1 errors.

To resolve the conflict, connect to the hosts were you know the correct file is located at and execute the following

$ csync2 -f /etc/ssh/sshd_conf
$ csync2 -x

Resetting a csync2 cluster

Resolves the following errors:

• ERROR from peer 10.0.0.1: File is also marked dirty here!
• Database backend is exceedingly busy => Terminating (requesting retry).
• ERROR from peer 10.0.0.1: Connection closed.

First of all, make sure that csync2 process is running. Then connect to all servers, and update the csync2 database.

$ csync2 -cIr /

IMPORTANT only perform the next steps on the master

Go to the server with the new files or corrected state (may be master =) Get all differences between master and slaves and mark for sync

$ csync2 -TUXI

Reset database on master to winn all conflicts and sync data to all slaves

$ csync2 -fr /
$ csync2 -xr /

Connect now again to all other servers too and run to check the sync state

$ csync2 -T