NFS High Availability setup

NFS is a tricky beast to setup for high availability. Without proper configuration NFS clients tend to hang waiting for i/o completion on the shares. This guide exposes the Linux NFS servers configuration for smooth failover.

OpenSVC HA setup

Create a HA service, using the howto.ha howto.

Make sure the <OSVCETC>/nfssvc.d symlink points to a directory hosted on a shared filesystem, handled by the nfssvc OpenSVC service. This howto uses /nfssvc as the root service shared filesystem.

On the master node

$ mkdir -p /nfssvc/etc/init.d
$ ln -s /nfssvc/etc/init.d /etc/opensvc/nfssvc.d

NFS configuration

Linux NFS service uses /var/lib/nfs to store both node-private and service-private data. The tricky part of the HA setup is to separate this data.

NFS server startup

NFS startup will be handled by the OpenSVC service. Stop the NFS service and inhibit its launch at server startup.

On both nodes

$ /etc/init.d/nfs stop
$ /etc/init.d/nfslock stop

$ chkconfig nfs off
$ chkconfig nfslock off

Create the OpenSVC service startup script.

On the master node:

$ cat <<EOF >/etc/opensvc/nfssvc.d/nfs
#!/bin/bash

nfsstart(){
        /etc/init.d/nfs start
        /etc/init.d/nfslock start
}

nfsstop(){
        /etc/init.d/nfslock stop
        /etc/init.d/nfs stop
}

case "$1" in
start)
        nfsstart
        ;;
stop)
        nfsstop
        ;;
restart)
        nfsstop
        nfsstart
        ;;
*)
        echo "usage $0 { start | stop | restart }"
        ;;
esac

exit 0
EOF

And activate this script.

On the master node

$ cd /etc/opensvc/nfssvc.d
$ ln -s nfs S10nfs
$ ln -s nfs K10nfs

Node private data

The data that must remain local to each node is the RPC pipefs pseudo filesystem. It is mounted by default under /var/lib/nfs/rpc_pipefs. As /var/lib/nfs will be moved to the shared filesystem, we need to change the location of this mount point.

Create the new mount point.

On both nodes

$ mkdir /var/lib/rpc_pipefs

Change these system configuration files to use this new mountpoint.

On both nodes

/etc/modprobe.d/modprobe.conf.dist
/etc/idmapd.conf

Service private data

/var/lib/nfs contains data essential for nfs client sessions takeover. Thus, this directory must follow the service in case of failover.

On the master node

$ mkdir -p /nfssvc/var/lib
$ mv /var/lib/nfs /nfssvc/var/lib/nfs

The exports list should also move with the service, to avoid configuration drift between the 2 nodes.

On the master node

$ mv /etc/exports /etc/opensvc/nfssvc.d/

On both nodes

$ ln -sf /nfssvc/var/lib/nfs /var/lib/nfs
$ ln -sf /etc/opensvc/nfssvc.d/exports /etc/exports

Configure nfs to listen on the service IP address

On both nodes

Modify STATD_HOSTNAME in /etc/sysconfig/nfs

Epilog

Reboot the nodes to activate the new rpc_pipefs location and start testing failovers.