My-CTDB

Revision as of 18:15, 22 February 2020 by StefanKania (talk | contribs)

Introduction

CTDB is a clustered database component in clustered Samba that provides a high-availability load-sharing CIFS server cluster.

The main functions of CTDB are:

  • Provide a clustered version of the TDB database with automatic rebuild/recovery of the databases upon node failures.
  • Monitor nodes in the cluster and services running on each node.
  • Manage a pool of public IP addresses that are used to provide services to clients. Alternatively, CTDB can be used with LVS.

Combined with a cluster filesystem CTDB provides a full high-availablity (HA) environment for services such as clustered Samba, NFS and other services.

Setting up CTDB

After setting up the cluster filesystem you can set up a CTDB-cluster. To user CTDB you have to install the ctdb-package for your distribution. After installing the package with all it's dependencies you will find a directory /etc/ctdb. Inside tis directory you need some configuration files for CTDB.

Let's take a look at the files needed for configuring CTDB.

File Content
/etc/ctdb/ctdb.conf Basic configuration
/etc/ctdb/script.options Setting options for event-scripts
/etc/ctdb/nodes All IP-addresses of all nodes
/etc/ctdb/public_addresses Dynamic IP-addresses for all nodes

The ctdb.conf file

The ctdb.conf file has changed a lot from the old configuration style (< Samba 4.9). This file will no longer be used to configure the different services managed by CTDB. At the moment the only setting you have to do inside the file is setting up the recovery lock file. This file is used by all nodes to check if it's possible to lock files inside the cluster for exclusive use. If you don't use a recovery lock file your cluster can run into a split brain situation. By default the 'recovery lock' is NOT set. You should not use CTDB without a recovery lock unless you know what you are doing. The variable must point to a file inside your mounted gluster-volume. To use the recovery lock enter the following line into /etc/ctdb/ctdb.conf} on both nodes:

\begin{lstlisting}[captionpos=b,label=recovery-lock,caption=Defining the recovery lock] recovery lock = /glusterfs/ctdb.lock \end{lstlisting}

The \textit{recovery lock} setting needs to be in the \textit{[cluster]} section.

\textbf{Hint!}\newline\fbox{\parbox{\linewidth}{You don`t have to create the recovery lock file, it will be created by CTDB on the first start of the CTDB-daemon}}