Linux Bidirectional Replication Configuration Example

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This article is about configuring Linux real time bidirectional data replication and file synchronization (file sync) in EDpCloud software.

Introduction to Linux bidirectional replication for backup and file mirroring

Bidirectional file replication: one to oneIn this blog, we will learn how to configure EDpCloud software for Linux bidirectional data replication and to synchronize data back and forth between two Linux servers (For backup purposes, online file mirroring, or process automation). Bidirectional replication is also known as two-way sync. Whenever a file changes in one server, it also changes in the other server, hence mirroring files and the content of the two servers. Any changes that happen in one server will also happen on the other server and vice-versa.

Linux Bidirectional Replication Server

Our objective here is to backup one Linux server to another and vice-versa.


Download Linux Bidirectional Replication Software

For example, if you modify file “foo” on a server called “svr1”, file foo will also be modified on server “svr2” and vice-versa(by sending only the deltas or the part of the file that changed).

You can also do the same thing I describe hereunder windows, but I will specifically discuss the Linux Bidirectional Replication here.

Without delay, let’s jump in and see how we can configure Linux real time bidirectional replication and filesyc to mirror file systems on servers or virtual machines.


Please read this article first:

Requirements for Linux Bidirectional Replication and remote file mirroring

1. Download and install EDpCloud by visiting  https://www.enduradata.com/downloads. If you have 64 bit Linux, make sure you download the 64-bit package; otherwise, download the x86 package (32 bit).

2. Install EDpCloud replication software

Details about the installation can be found in the articles cited above.

3. Have your list of directories or files that you want to replicate handy: This is the list of directories that you want to monitor in real time for backup.

Configure Linux bidirectional data replication and file synchronization

1.  cd $ED_BASE_DIR/etc

2.  vi includes and add all the directories you want to include in the replication

The includes and excludes files use regular expressions. For more information, read the post on includes and excludes:

Excluding and including files from data synchronization.

Edit data replication includes file.

Your includes much have only the directories you want to be included. If you don’t have an include file, everything is included by default.

Add the following two lines using a text editor (or the browser-based GUI). This will allow the servers to only include the files that match the patterns below in the bidirectional data replication. Make sure you do the same on both servers.

^/data/
^/data/.*

This will only replicate and mirror files that are under /data and the directory /data itself.

Edit  Linux replication excludes

Again see the post about excluding files from replication. It is critical that you exclude all directories such as etc, var, etc. The default excludes such a list. I cannot stress enough how important it is to use includes and excludes to avoid mirroring files in /etc such as the passwords, the hostnames, and IP addresses. Make sure you use the includes to specify what to replicate.

Install FUSE if your system does not have it

EDpCloud requires fuse. You can find the sources under $ED_BASE_DIR/edpcloud/src

as root:

[ Please replace the version numbers if needed ]

cd $ED_BASE_DIR/edpcloud/src

tar xvf  ed_fuse-2.9.5.tar.gz

cd fuse-2.9.5

You can install fuse under /usr/local or under $ED_BASE_DIR/edpcloud

./configure –prefix=/usr/local
make
make install

Now add /usr/local/lib

/etc/ld.so.conf (assuming you installed fuse there)

modprobe fuse
ldconfig

Edit eddist.cfg  replication configuration

We will need to create two links (also called replication sets). One going from svr1 to svr2 (l1) and one going from svr2 to svr1 (2).  These will allow us to have replication in two directions thus the name “bidirectional replication” also known as “two way sync”. File changes that take place on svr1 will be synchronized with svr2 using the link (repset) l1. File changes that take place on svr2 will be synchronized with svr1 using link l2.

Here is the content of eddist.cfg

<?xml version="1.0" encoding="UTF-8"?>

<config name="enduradata" password="Addoud4d4ch1n1gh4T4s4" workers="4">

    <link name="l1" password="foo">
        <sender hostname="svr1" />
        <receiver hostname="svr2" storepath="/" />
    </link>
    <link name="l2" password="foo">
        <sender hostname="svr2"  />
        <receiver hostname="svr1" storepath="/" />
    </link>

</config>

Notice that the data replication configuration above will not propagate deletes between the two systems. To propagate deletes, we need to add the keyword deletes=”1″ to eddist.cfg as the following example shows (But don’t do deletes=”1″ unless you know what you are doing).

<?xml version="1.0" encoding="UTF-8"?>

<config name="enduradata" password="Addoud4d4ch1n1gh4T4s4" workers="4">

    <link name="l1" password="foo">
        <sender hostname="svr1" />
        <receiver hostname="svr2" storepath="/" deletes="1"/>
    </link>
    <link name="l2" password="foo">
        <sender hostname="svr2"  />
        <receiver hostname="svr1" storepath="/" deletes="1"/>
    </link>

</config>

Now the directory /data will be mirrored between the two servers svr1 and svr2. Any changes made on svr1 are made on svr2, and any changes made on svr2 are made on svr1 using file synchronization. Please note that there is no distributed lock manager between the two servers, and the last writer wins (Same behavior as with NFS).

Start EDpCloud for Linux file replication services

Run the following command to start EDpCloud, and you will be on your way to synchronize data between the two servers in real time thus ensuring that data is backed up between the two.


. $ED_BASE_DIR/bin/edpcloud.sh startall

Run edstat to make sure edpcloud is running before you proceed to the next step. Do not proceed unless edpcloud is running without the real-time configuration. If you run into problems, check eddist.log to find out what is wrong with your data replication (Other logs can be found in  $ED_BASE_DIR/logs)

Replicate some data by using:

edq -l linkname -r receivername -n dir_or_filename

run edstat again and verify that your files were replicated to the receiver side.

Do all the previous steps for all hosts in eddist.cfg. Once scheduled and on-demand replication and backup are working, proceed to configure the real time replication and synchronization.

Edit edfsmonitor.cfg, the Linux Real Time Replication Configuration

Add this line to the file and save it.
/data

This tells EDpcloud to monitor /data for changes and queue them for replication to the remote server.

Now that real time replication is configured, you need to start the real time file system changes, monitor:

Source in the environment (notice the dot):

cd /tmp

     .   $ED_BASE_DIR/bin/enduradata_env

edstartuwfs.sh

if all worked, you should see the directories in edfsmonitor.cfg mounted (use df to see what is mounted)

Your real time bidirectional replication is now configured, and any files that change in directories, listed in edfsmonitor.cfg, on one system are replicated to the other remote system.

QUESTIONS?

The following is a list of related articles you may be interested in:

Linux Bidirectional Replication Configuration Example was last modified: April 8th, 2021 by aRoot

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