Need to Sync Two CentOS 8 Servers Using File Replication?
At Bobcares, we often get requests from our customers to sync Centos servers as a part of our Server Management Services.
Today let’s see how our Support Engineers get this done with ease.
Basic Configuration required for Syncing Two CentOS 8 Servers Using File Replication
Our Support Engineers Synchronize data between two CentOS 8 servers running Apache is done using Lsyncd.
1. Before setting up Lsyncd we have to add the software repository that contains the Lsyncd package.
The following command can be used to add EPEL Repo:
root@alt ~]# yum -y install epel-releaseThe installation will take a moment, and we will see a decent amount of output. Once it says “Complete!” we can move on.
[root@alt ~]# yum -y install epel-release Loaded plugins: fastestmirror, langpacks, priorities Loading mirror speeds from cached hostfile 1 packages excluded due to repository priority protections Resolving Dependencies --> Running transaction check ---> Package epel-release.noarch 0:7-11 will be installed --> Finished Dependency Resolution Dependencies Resolved ===================================================================== Package Arch Version Repository Size ===================================================================== Installing: epel-release noarch 7-11 system-extras 15 k Transaction Summary ===================================================================== Install 1 Package Total download size: 15 k Installed size: 24 k Downloading packages: epel-release-7-11.noarch.rpm | 15 kB 00:00:00 Running transaction check Running transaction test Transaction test succeeded Running transaction Installing : epel-release-7-11.noarch 1/1 Verifying : epel-release-7-11.noarch 1/1 Installed: epel-release.noarch 0:7-11 Complete!
To check whether the repository we set up is enabled or not we can use the following command:
[root@alt ~]# vim /etc/yum.repos.d/epel.repoAfter this ensure that the repo is set to enabled=1.
[epel] name=Extra Packages for Enterprise Linux 7 - $basearch #baseurl=http://download.fedoraproject.org/pub/epel/7/$basearch metalink=https://mirrors.fedoraproject.org/metalink?repo=epel-7&arch=$basearch failovermethod=priority ***enabled=1*** gpgcheck=1 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-7
2. Then Install the Lsyncd Software
Now we can install the Lsyncd software using the following command.
root@alt ~]# yum -y install lsyncdThis process will take a few moments to complete, and then we can continue the set up once we see “Complete!”.
[root@alt ~]# yum -y install lsyncd Loaded plugins: fastestmirror, langpacks, priorities Loading mirror speeds from cached hostfile epel/x86_64/metalink | 16 kB 00:00:00 * epel: mirrors.liquidweb.com epel | 5.4 kB 00:00:00 (1/3): epel/x86_64/group_gz | 90 kB 00:00:00 (2/3): epel/x86_64/updateinfo | 1.0 MB 00:00:00 (3/3): epel/x86_64/primary_db | 6.9 MB 00:00:00 166 packages excluded due to repository priority protections Resolving Dependencies --> Running transaction check ---> Package lsyncd.x86_64 0:2.2.2-1.el7 will be installed --> Finished Dependency Resolution Dependencies Resolved ====================================================================== Package Arch Version Repository Size ====================================================================== Installing: lsyncd x86_64 2.2.2-1.el7 epel 83 k Transaction Summary ====================================================================== Install 1 Package Total download size: 83 k Installed size: 227 k Downloading packages: warning: /var/cache/yum/x86_64/7/epel/packages/lsyncd-2.2.2-1.el7.x86_64.rpm: Header V3 RSA/SHA256 Signature, key ID 352c64e5: NOKEY] 0.0 B/s | 0 B --:--:-- ETA Public key for lsyncd-2.2.2-1.el7.x86_64.rpm is not installed lsyncd-2.2.2-1.el7.x86_64.rpm | 83 kB 00:00:00 Retrieving key from file:///etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-7 Importing GPG key 0x352C64E5: Userid : "Fedora EPEL (7) <epel@fedoraproject.org>" Fingerprint: 91e9 7d7c 4a5e 96f1 7f3e 888f 6a2f aea2 352c 64e5 Package : epel-release-7-11.noarch (@system-extras) From : /etc/pki/rpm-gpg/RPM-GPG-KEY-EPEL-7 Running transaction check Running transaction test Transaction test succeeded Running transaction Installing : lsyncd-2.2.2-1.el7.x86_64 1/1 Verifying : lsyncd-2.2.2-1.el7.x86_64 1/1 Installed: lsyncd.x86_64 0:2.2.2-1.el7 Complete!
3. After that configure SSH on Master
To ensure the master host can push files to the slave hosts without requiring user intervention we will configure SSH on Master
We can create the SSH key using the following command:
root@host # ssh-keygen -t rsa (or)
root@host # ssh-keygen -t rsa -b 4096 -C "$(whoami)@$(hostname)-$(date -u +%Y-%m-%d-%H:%M:%S%z)"We can use the second command to generate a stronger key.
Here, we will use the defaults and no added password.
Enter passphrase (empty for no passphrase): Enter same passphrase again: Your identification has been saved in /home/username/.ssh/id_rsa. Your public key has been saved in /home/username/.ssh/id_rsa.pub. The key fingerprint is: SHA256:rCwcRH+3vxiIsrkrwikDaE1UlTi8vr0g/wOfwSowCsw user@domain.com-2019-08-21-13:14:45+0000 The key's randomart image is: +---[RSA 4096]----+ |. . . . | | = o . . | |o.= . . . . | |oDo . . . . . | |B. .. Y . | |O+.. o . . | |O++.o o . . . | |=*. . ... . . o. | |.o.=+.++. . . | +----[SHA256]-----+
After the SSH keys are generated, we will transfer the public key over to our slave host so that it will allow us to authenticate and access that host without needing to enter a password.
We can transfer the key using the following command:
root@alt [~]# ssh-copy-id root@opt.thisisnotadomain.comTo ensure that lsyncd can utilize the SSH keys we created, we need to modify the SSH config file on the master to add a few snippets of information.
root@alt [~]# vim ~/.ssh/configEdit the config file using vim, and add the following into it.
Host dest_host Hostname 172.16.144.32 User root IdentityFile ~/.ssh/id_rsa
Synchronizing using Lsyncd
To Sync Two CentOS 8 Servers Using File Replication with Lsyncd we need to follow the below steps:
1. Configure Lsyncd on Master
Next, we need to modify the Lsyncd configuration file. We will need to specify the following settings:
Edit the config file using the vim command.
root@alt [~]# vim /etc/lsyncd.confThen we need to modify the configurations
settings {
logfile = "/var/log/lsyncd/lsyncd.log",
statusFile = "/var/log/lsyncd/lsyncd-status.log",
statusInterval = 10
}
-- Slave server configuration
sync {
default.rsync,
source="/var/www/",
target="IP:/var/www/",
rsync = {
compress = true,
acls = true,
verbose = true,
owner = true,
group = true,
perms = true,
rsh = "/usr/bin/ssh -p 22 -o StrictHostKeyChecking=no"
}
}
After making the edits, run the following commands to start and enable the service.
[root@alt lsyncd]# systemctl start lsyncd
[root@alt lsyncd]# systemctl enable lsyncd
Created symlink from /etc/systemd/system/multi-user.target.wants/lsyncd.service to /usr/lib/systemd/system/lsyncd.service.
We can see that Lsyncd is running, now we need to verify that it is monitoring the folder for any changes in the status log.
root@alt [~]# cd /var/log/lsyncd [root@alt lsyncd]# tail lsyncd.status Lsyncd status report at Thu Feb 6 10:07:37 2020 Sync1 source=/var/www/html/ There are 0 delays Excluding: Nothing. Inotify watching 1 directories 1: /var/www/html/
From the logs we can see that it is being synced from the master to the slave server.
Since we have the Lsyncd service running, it will start when the system is rebooted and continuously monitor any changes and push the changes across to the slave node.
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Conclusion
To conclude, saw how our Support Engineers sync two CentOS 8 servers using file replication in a few steps.
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