Scenario

We are building a second web server with a hope of installing a load balancer soon. We came into a problem where we have to synchronize the file contents between multiple servers. The solution we’re opting is to install and mount a shared network folder (NFS) visible from both web servers. The shared folder lives on its own server (aka file system server).

It is assumed:

1. The file system server host (Master) is 12.0.10.10
2. The client is 12.0.20.20
3. The folder to be shared on master is /var/www/vhosts
4. The folder will be mounted to /mnt/nfs/var/www/vhosts on client

Creating a NFS Share on the File System Server

Perform these steps on the file system server (aka “Master”):

1. Install nfs-utils and nfs-utils-lib package using yum:
   yum install nfs-utils nfs-utils-lib
   Use yum list installed to check if the packages are already installed
2. Turn on nfs service so it automatically starts on boot
   chkconfig nfs on
   Use chkconfig --list to check status of all services
3. Start rpcbind and nfs service
   service rpcbind start
service nfs start
4. Edit /etc/exports file and add following line at the end
   /var/www/vhosts 12.0.20.20(rw,sync,no_root_squash,no_subtree_check)
   See here for explanation of the options
5. Run following command to apply the changes
   exportfs -a

Mounting it on the Client

Following steps will mount the network folder permanently (folder will automatically re-mount on server reboot). Perform this on the client server:

1. Similar to server, ensure nfs-utils and nfs-utils-lib are installed
   yum install nfs-utils nfs-utils-lib
2. Create the directory that will hold the mount (mount point)
   mkdir -p /mnt/nfs/var/www/vhosts
3. Edit /etc/fstab file and append following line
   12.0.10.10:/var/www/vhosts /mnt/nfs/var/www/vhosts nfs defaults 0 0
4. Run mount /mnt/nfs/var/www/vhosts to apply the mounting. Check if the mounting is successful using df -h

OS User on Master and Client

To ensure file system operations are consistent, consider propagating same OS user setup between the master and client. Note that although same username exists on both master and client they don’t necessarily have the same UID.

• Checking uid and group of user jim:
  $ id jim
uid=506(jim) gid=505(xyzco) groups=505(xyzco)
  (jim has uid 506 and belongs to group xyzco)
• Adding a new user jim with uid 506
  useradd -u 506 jim
• Adding jim to the group xyzco
  usermod -G xyzco jim
• Setting / resetting password for jim
  passwd jim

Thanks To

• Digital Ocean: How To Set Up an NFS Mount on CentOS 6
• RHEL 5.1 Manual Chapter 19: Network File System (NFS)
• RHEL 6: Storage and Administration Guide: Running NFS Behind a Firewall

Additional Reading

• Rackspace Knowledge Center: Prepare Your Cloud Block Storage Volume