GlusterFS CTDB Integration

Red Hat K.K. All rights reserved.
GlusterFS / CTDB Integration
v1.0 2013.05.14
Etsuji Nakai
Senior Solution Architect
Red Hat K.K.

Red Hat K.K. All rights reserved. 2
$ who am i

Etsuji Nakai (@enakai00)
●
Senior solution architect and cloud evangelist at
Red Hat K.K.
●
The author of “Professional Linux Systems” series.
●
Available in Japanese. Translation offering from
publishers are welcomed ;-)
Professional Linux Systems
Technology for Next Decade
Deployment and Management
Network Management

Contents

CTDB Overview

Why does CTDB matter?

CTDB split-brain resolution

Configuration steps for demo set-up

Summary

Disclaimer

This document explains how to setup clustered Samba server using GlusterFS and CTDB
with the following software components.
●
Base OS, Samba, CTDB: RHEL6.4 (or any of your favorite clone)
●
GlusterFS: GlusterFS 3.3.1 (Community version)
●
http://download.gluster.org/pub/gluster/glusterfs/3.3/3.3.1/

Since this is based on the community version of GlusterFS, you cannot receive a commercial
support from Red Hat for this configuration. If you need a commercial support, please
consider using Red Hat Storage Server(RHS). In addition, there are different conditions for
a supportable configuration with RHS. Please consult sales representatives from Red Hat
for details.

Red Hat accepts no liability for the content of this document, or for the consequences of
any actions taken on the basis of the information provided. Any views or opinions
presented in this document are solely those of the author and do not necessarily represent
those of Red Hat.

CTDB Overview

What's CTDB?

TDB = Trivial Database
●
Simple backend DB for Samba, used to store user info, file lock info, etc...

CTDB = Clustered TDB
●
Cluster extension of TDB, necessary for
multiple Samba hosts configuration to
provide the same filesystem contents.
All clients see the same contents
through different Samba hosts.
Samba Samba Samba
・・・
Shared Filesystem

What's wrong without CTDB?

Windows file locks are not shared among Samba hosts.
●
You would see the following alert when someone is opening the same file.
●
Without CTDB, if others are opening the same
file through a different Samba host from you,
you never see that alert.
●
This is because file lock info is stored in the
local TDB if you don't use CTDB.
●
CTDB was initially developed as a shared TDB
for multiple Samba hosts to overcome this
problem.
xxx.xls
Windows file locks
are not shared.
Locked! Locked!

CTDB interconnect
(heartbeat) network
Yet another benefit of CTDB

Floating IP's can be assigned across hosts for the transparent failover.
●
When one of the hosts fails, the floating IP is moved to another host.
●
Mutual health checking is done through the CTDB interconnect (so called
“heartbeat”) network.
●
CTDB can also be used for NFS server cluster to provide the floating IP
feature. (CTDB doesn't provide shared file locking for NFS though.)
Floating IP#1
・・・
Floating IP#2 Floating IP#N
Floating IP#1
・・・
Floating IP#2 Floating IP#N
Floating IP#1

Why does CTDB matter?

Access path of GlusterFS native client

The native client directly communicates to all storage nodes.
●
Transparent failover is implemented on the client side. When the client
detects the node failure, it accesses the replicated node.
●
Floating IP is unnecessary by design for the native client.
file01 file02 file03
・・・
GlusterFS Storage Nodes
file01, file02, file03
GlusterFS
Native Client
GlusterFS Volume
Native client sees the volume
as a single filesystem
The real locations of files are
calculated on the client side.

CIFS/NFS usecase for GlusterFS

The downside of the native client is it's not available for Unix/Windows.
●
You need to rely on CIFS/NFS for Unix/Windows clients.
●
In that case, windows file lock sharing and floating IP feature are not in
GlusterFS. It should be provided with an external tool.

CTDB is the tool for it ;-)
・・・
CIFS/NFS Client
CIFS/NFS client connects to
just one specified node.
GlusterFS storage node acts
as a proxy “client”.
Different clients can connect to
different nodes.
DNS round-robin may work for it.

Network topology overview without CTDB
Storage Nodes
CIFS/NFS Clients
GlusterFS interconnect
CIFS/NFS Access segment
...

If you don't need the floating IP/Windows file lock, you can go without CTDB.
●
NFS file lock sharing (DNLM) is provided by GlusterFS's internal NFS server.

Although it's not mandatory, you can separate CIFS/NFS access segment from
the GlusterFS interconnect for the sake of network performance.
Samba Samba Samba Samba
glusterd glusterd glusterd glusterd

Network topology overview with CTDB
Storage Nodes
CIFS/NFS Clients
CIFS/NFS access segment
...

If you use CTDB with GlusterFS, you need to add an independent CTDB
interconnect (heartbeat) segment for the reliable cluster.
●
The reason will be explained later.
CTDB interconnect
(Heartbeat)

Demo - Seeing is believing!
http://www.youtube.com/watch?v=kr8ylOBCn8o

CTDB split-brain resolution

What's CTDB split-brain?

When heartbeat is cut-off from any reason (possibly network problem) while cluster nodes
are still running, there must be some mechanism to choose which "island" should survive
and keep running.
●
Without this mechanism, the same floating IP's are assigned on both islands. This is not specific
to CTDB, every cluster system in the world needs to take care of the “split-brain”.

In the case of CTDB, a master node is elected though the "lock file" on the shared
filesystem. An island with the master node survives. Especially, in the case of GlusterFS,
the lock file is stored on the dedicated GlusterFS volume, called "lock volume".
●
The lock volume is locally mounted on each storage node. If you share the CTDB interconnect with
GlusterFS interconnect, access to the lock volume is not guaranteed when the heartbeat is cut-
off, resulting in an unpredictable condition.
Storage Nodes
CTDB interconnect
(Heartbeat)
Lock Volume
Master
The master takes an exclusive
lock on the lock file.

Typical volume config seen from storage node
# df
Filesystem           1Kblocks      Used Available Use% Mounted on
/dev/vda3              2591328   1036844   1422852  43% /
tmpfs                   510288         0    510288   0% /dev/shm
/dev/vda1               495844     33450    436794   8% /boot
/dev/mapper/vg_brickslv_lock
                         60736      3556     57180   6% /bricks/lock
/dev/mapper/vg_brickslv_brick01
                       1038336     33040   1005296   4% /bricks/brick01
localhost:/lockvol      121472      7168    114304   6% /gluster/lock
localhost:/vol01       2076672     66176   2010496   4% /gluster/vol01
# ls l /gluster/lock/
total 2
rwrr. 1 root root 294 Apr 26 15:43 ctdb
rw. 1 root root   0 Apr 26 15:57 lockfile
rwrr. 1 root root  52 Apr 26 15:56 nodes
rwrr. 1 root root  96 Apr 26 15:04 public_addresses
rwrr. 1 root root 218 Apr 26 16:31 smb.conf
Locally mounted
lock volume.
Locally mounted data volume,
exported with Samba.
Lock file to elect the master.
Common config files can be
placed on the lock volume.

What about sharing CTDB interconnect with
the access segment?

No, it doesn't work.

When NIC for the access segment fails, the cluster detects the heartbeat failure
and elects a master node through the lock file on the shared volume. However if
the NIC failed node has the lock, it becomes the master although it doesn't serve
to clients.
●
In reality, CTDB event monitoring detects the NIC failure and the node becomes "CTDB
UNHEALTHY" status, too.

CTDB event monitoring

CTDB provides a custom event monitoring mechanism which can be used to
monitor application status, NIC status, etc...
●
Monitoring scripts are stored in /etc/ctdb/events.d/
●
They need to implement handlers to pre-defined events.
●
They are called in the order of file name when some event occurs.
●
Especially, "monitor" event is issued every 15seconds. If the "monitor" handler of some
script exits with non-zero return code, the node becomes "UNHEALTHY", and will be
rejected from the cluster.
●
For example, “10.interface” checks the link status of NIC on which floating IP is
assigned.
●
See README for details - http://bit.ly/14KOjlC
# ls /etc/ctdb/events.d/
00.ctdb       11.natgw           20.multipathd  41.httpd  61.nfstickle
01.reclock    11.routing         31.clamd       50.samba  70.iscsi
10.interface  13.per_ip_routing  40.vsftpd      60.nfs    91.lvs

Configuration steps for demo set-up

Step1 – Install RHEL6.4

Install RHEL6.4 on storage nodes.
●
Scalable File System Add-On is required for XFS.
●
Resilient Storage Add-On is required for CTDB packages.

Configure public key ssh authentication between nodes.
●
This is for an administrative purpose.

Configure network interfaces as in the configuration pages.
192.168.122.11  gluster01
192.168.122.12  gluster02
192.168.122.13  gluster03
192.168.122.14  gluster04
192.168.2.11    gluster01c
192.168.2.12    gluster02c
192.168.2.13    gluster03c
192.168.2.14    gluster04c
192.168.1.11    gluster01g
192.168.1.12    gluster02g
192.168.1.13    gluster03g
192.168.1.14    gluster04g
/etc/hosts
NFS/CIFS Access Segment
CTDB Interconnect
GlusterFS Interconnect

Step1 – Install RHEL6.4

Configure iptables on all nodes
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
A INPUT m state state ESTABLISHED,RELATED j ACCEPT
A INPUT p icmp j ACCEPT
A INPUT i lo j ACCEPT
A INPUT m state state NEW m tcp p tcp dport 22 j ACCEPT
A INPUT m state state NEW m tcp p tcp dport 24007:24050 j ACCEPT
A INPUT m state state NEW m tcp p tcp dport 38465:38468 j ACCEPT
A INPUT j REJECT rejectwith icmphostprohibited
A FORWARD j REJECT rejectwith icmphostprohibited
COMMIT
/etc/sysconfig/iptables
# vi /etc/sysconfig/iptables
# service iptables restart
CTDB
CIFS
portmap
NFS/NLM
Bricks
CIFS

Step2 – Prepare bricks

Create and mount brick directories on all nodes.
# pvcreate /dev/vdb
# vgcreate vg_bricks /dev/vdb
# lvcreate n lv_lock L 64M vg_bricks
# lvcreate n lv_brick01 L 1G vg_bricks
# yum install y xfsprogs
# mkfs.xfs i size=512 /dev/vg_bricks/lv_lock
# vi mkfs.xfs i size=512 /dev/vg_bricks/lv_brick01
# echo '/dev/vg_bricks/lv_lock /bricks/lock xfs defaults 0 0' >> /etc/fstab
# echo '/dev/vg_bricks/lv_brick01 /bricks/brick01 xfs defaults 0 0' >> /etc/fstab
# mkdir p /bricks/lock
# mkdir p /bricks/brick01
# mount /bricks/lock
# mount /bricksr/brick01
/dev/vdb
lv_lock
lv_brick01
vg_bricks
Mount on /bricks/lock, used for lock volume.
Mount on /bricks/brick01, used for data volume.

Step3 – Install GlusterFS and create volumes

Install GlusterFS packages on all nodes
# wget O /etc/yum.repos.d/glusterfsepel.repo
  http://download.gluster.org/pub/gluster/glusterfs/3.3/3.3.1/RHEL/glusterfsepel.repo
# yum install y rpcbind glusterfsserver
# chkconfig rpcbind on
# service rpcbind start
# service glusterd start
# gluster peer probe gluster02g
# gluster vol create lockvol replica 2
    gluster01g:/bricks/lock gluster02g:/bricks/lock
    gluster03g:/bricks/lock gluster04g:/bricks/lock
# gluster vol start lockvol
# gluster vol create vol01 replica 2
    gluster01g:/bricks/brick01 gluster02g:/bricks/brick01
    gluster03g:/bricks/brick01 gluster04g:/bricks/brick01
# gluster vol start vol01
Do not auto start glusterd
with chkconfig.
Need to specify
GlusterFS interconnect NICs.

Configure cluster and create volumes from gluster01

Step4 – Install and configure Samba/CTDB
●
Create the following config files on the shared volume.
# yum install y samba sambaclient ctdb
# mkdir p /gluster/lock
# mount t glusterfs localhost:/lockvol /gluster/lock
Do not auto start smb
and ctdb with chkconfig.
CTDB_PUBLIC_ADDRESSES=/gluster/lock/public_addresses
CTDB_NODES=/etc/ctdb/nodes
# Only when using Samba. Unnecessary for NFS.
CTDB_MANAGES_SAMBA=yes
# some tunables
CTDB_SET_DeterministicIPs=1
CTDB_SET_RecoveryBanPeriod=120
CTDB_SET_KeepaliveInterval=5
CTDB_SET_KeepaliveLimit=5
CTDB_SET_MonitorInterval=15
/gluster/lock/ctdb
# yum install y rpcbind nfsutils
# chkconfig rpcbind on
# service rpcbind start

Install Samba/CTDB packages on all nodes

If you use NFS, install the following packages, too.

Configure CTDB and Samba only on gluster01

192.168.2.11
192.168.2.12
192.168.2.13
192.168.2.14
/gluster/lock/nodes
192.168.122.201/24 eth0
192.168.122.202/24 eth0
192.168.122.203/24 eth0
192.168.122.204/24 eth0
/gluster/lock/public_addresses
[global]
workgroup = MYGROUP
server string = Samba Server Version %v
clustering = yes
security = user
passdb backend = tdbsam
[share]
comment = Shared Directories
path = /gluster/vol01
browseable = yes
writable = yes
/gluster/lock/smb.conf
CTDB cluster nodes.
Need to specify CTDB interconnect NICs.
Floating IP list.
Samba config.
Need to specify “clustering = yes”


Set SELinux permissive for smbd_t on all nodes due to the non-standard smb.conf location.
●
We'd better set an appropriate seculity context, but there's an open issue for using chcon with
GlusterFS.
●
https://bugzilla.redhat.com/show_bug.cgi?id=910380
# mv /etc/sysconfig/ctdb /etc/sysconfig/ctdb.orig
# mv /etc/samba/smb.conf /etc/samba/smb.conf.orig
# ln s /gluster/lock/ctdb /etc/sysconfig/ctdb
# ln s /gluster/lock/nodes /etc/ctdb/nodes
# ln s /gluster/lock/public_addresses /etc/ctdb/public_addresses
# ln s /gluster/lock/smb.conf /etc/samba/smb.conf
# yum install y policycoreutilspython
# semanage permissive a smbd_t

Create symlink to config files on all nodes.


Create the following script for start/stop services
#!/bin/sh
function runcmd {
        echo exec on all nodes: $@
        ssh gluster01 $@ &
        ssh gluster02 $@ &
        ssh gluster03 $@ &
        ssh gluster04 $@ &
        wait
}
case $1 in
    start)
        runcmd service glusterd start
        sleep 1
        runcmd mkdir p /gluster/lock
        runcmd mount t glusterfs localhost:/lockvol /gluster/lock
        runcmd mkdir p /gluster/vol01
        runcmd mount t glusterfs localhost:/vol01 /gluster/vol01
        runcmd service ctdb start
        ;;
    stop)
        runcmd service ctdb stop
        runcmd umount /gluster/lock
        runcmd umount /gluster/vol01
        runcmd service glusterd stop
        Runcmd pkill glusterfs
        ;;
esac
ctdb_manage.sh

Step5 – Start services

Now you can start/stop services.
●
After a few moments, ctdb status becomes “OK” for all nodes.
●
And floating IP's are configured on each node.
# ./ctdb_manage.sh start
# ctdb status
Number of nodes:4
pnn:0 192.168.2.11     OK (THIS NODE)
pnn:1 192.168.2.12     OK
pnn:2 192.168.2.13     OK
pnn:3 192.168.2.14     OK
Generation:1489978381
Size:4
hash:0 lmaster:0
hash:1 lmaster:1
hash:2 lmaster:2
hash:3 lmaster:3
Recovery mode:NORMAL (0)
Recovery master:1
# ctdb ip
Public IPs on node 0
192.168.122.201 node[3] active[] available[eth0] configured[eth0]
192.168.122.204 node[0] active[eth0] available[eth0] configured[eth0]

Step5 – Start services

Set samba password and check shared directories via one of floating IP's.
# pdbedit a u root
new password:
retype new password:
# smbclient L 192.168.122.201 U root
Enter root's password:
Domain=[MYGROUP] OS=[Unix] Server=[Samba 3.6.9151.el6]
Sharename       Type      Comment

share           Disk      Shared Directories
IPC$            IPC       IPC Service (Samba Server Version 3.6.9151.el6)
Domain=[MYGROUP] OS=[Unix] Server=[Samba 3.6.9151.el6]
Server               Comment

Workgroup            Master

Password DB is shared
by all hosts in the cluster.

Configuration hints

To specify the GlusterFS interconnect segment, "gluster peer probe" should be done for
the IP addresses on that segment.

To specify the CTDB interconnect segment, IP addresses on that segment should be
specified in "/gluster/lock/nodes" (symlink from "/etc/ctdb/nodes").

To specify the NFS/CIFS access segment, NIC names on that segment should be specified in
"/gluster/lock/public_addresses" (symlink from "/etc/ctdb/public_addresses") associated
with floating IP's.

To restrict NFS accesses for a volume, you can use “nfs.rpc-auth-allow” and “nfs.rpc-
auth-reject” volume options. (reject supersedes allow.)

The following tunables in "/gluster/lock/ctdb" (symlink from "/etc/sysconfig/ctdb") may
be useful for adjusting the CTDB failover timings. See the ctdbd man page for details.
●
CTDB_SET_DeterministicIPs=1
●
CTDB_SET_RecoveryBanPeriod=300
●
CTDB_SET_KeepaliveInterval=5
●
CTDB_SET_KeepaliveLimit=5
●
CTDB_SET_MonitorInterval=15

Summary

Summary

CTDB is the tool well combined with CIFS/NFS usecase for GlusterFS.

Network design is crucial to realize the reliable cluster, not only for
CTDB but also for every cluster in the world ;-)

Enjoy!

And one important fine print....
●
Samba is not well tested on the large scale GlusterFS cluster. The use of
CIFS as a primary access protocol on Red Hat Storage Server 2.0 is not
officially supported by Red Hat. This will be improved in the future versions.

WE CAN DO MORE
WHEN WE WORK TOGETHER
THE OPEN SOURCE WAY

GlusterFS CTDB Integration

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