A computer cluster consists of connected computers that work together as a single system. High availability (HA) systems are designed to avoid loss of service by managing failures and minimizing downtime. Key components of an HA cluster with openSUSE Leap include the Corosync messaging system, the Pacemaker resource manager, fencing devices to resolve split-brain situations, and shared storage solutions like DRBD. Setting up such a cluster involves installing openSUSE Leap on multiple VMs, configuring Corosync and Pacemaker for resource management and failover, implementing storage replication with DRBD, and testing the HA functionality of services like Nginx.

1. High Availability
Cluster with openSUSE
Leap
M. Edwin Zakaria
medwin@opensuse.org

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• Mohammad Edwin Zakaria
• Linux user since 1998
• openSUSE since 6.2 around 1999
https://en.opensuse.org/User:Medwin
• openSUSE member
https://connect.opensuse.org/show/Medwin
• openSUSE Indonesia

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What is
- Cluster ?
- High Availability ?

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Curious?
• A computer cluster consists of a set of loosely
or tightly connected computers that work
together so that, in many respects, they can be
viewed as a single system. Unlike grid
computers, computer clusters have each node
set to perform the same task, controlled and
scheduled by software

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Curious?
• High availability (HA) is a system that is
designed to avoid the loss of service by
reducing or managing failures as well as
minimizing planned downtime for the system.
We expect a service to be highly available
when life, health, and well-being, including
the economic well-being of a company, depend
on it.

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Curious?
• Harvard Research Group divide the HA into
several Availability Environment Classification
(AEC): AE4, AE3, AE2, AE1, AE0
• http://www.hrgresearch.com/pdf/AEC%20Defint
ions.pdf
• Other categories: continuous availability, fault
tolerance, disaster tolerance

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Once again what is cluster?
• High performance computing
• Load balancer (high capacity)
• High availability
‒ 99.99%
‒ MTBF (mean time between failure = total operating
time/total numbers of failure)
‒ Single point of failure

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Once again what is cluster?

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Challange in HA
• Murphy’s Law “If anything can go wrong, it will”
‒ Loss of data
‒ Service outage
• Flood, fire, earthquake, natural disaster,
hardware damage
‒ Can you afford a downtime?
‒ Can you afford low availability system?
‒ Cost of downtime?

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Different between HA term
• HA term is widely use
• VMware vSphere HA
‒ Closed source
‒ Hypervisor level and host hardware level
• openSUSE/SUSE HA
‒ Open source
‒ OS level
‒ Protect critical resources running on VM
‒ HA within Linux OS

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HA in Linux
• Started with heartbeat project in around 1990
• Now manage by ClusterLabs http://clusterlabs.org/
• The ClusterLabs stack, incorporating Corosync and
Pacemaker defines an Open Source, High
Availability cluster offering suitable for both small
and large deployments.
• Pacemaker has been around since 2004 and is
primarily a collaborative effort between Red Hat
and SUSE, they also receive considerable help and
support from the folks at LinBit and the community
in general.

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Hardware Consideration
• External network, high traffic, use FO or eth
bonding
• Communication network between cluster
node, use for messaging, membership,
STONITH
• Storage network, use FO or eth bonding
• Manage switch
• STONITH/fencing device
• Shared storage: NAS (nfs/cifs), SAN (fc/iscsi)

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Hardware Consideration

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Hardware Consideration

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Software Component
• Corosync
‒ messaging and membership
• Pacemaker
‒ Cluster resource management
• Resource Agents
‒ Manage and monitor availability of service
• Fencing device
‒ STONITH to ensure data integrity
• User interface
‒ Crmsh and Hawk

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Other component
• LVS linux virtual server
• HAproxy
• Shared file system: OCFS2, GFS2
• Block device replication: DRBD
• Shared storage: SAN
• Geo cluster

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More details
• Pacemaker :
Pacemaker is a cluster resource manager. It
achieves maximum availability for your cluster
resources by detecting and recovering from
node and resource-level failures by making use
of the messaging and membership capabilities
provided by your preferred cluster
infrastructure (either Corosync or Heartbeat).

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More details
• Corosync :
‒ provides cluster infrastructure functionality
‒ provides messaging and membership functionality
‒ maintains the quorum information.
‒ This feature has been utilized by pacemaker to
provide high availability solution.

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In short ...
• Corosync : A quorum system that notifies
applications when quorum is achieved or lost
• Pacemaker :
‒ To start/stop resources on a node according to the
score.
‒ To monitor resources according to interval.
‒ To restart resources if monitor fails.
‒ To fence/STONITH a node if stop operation fails.

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Pacemaker Corosync Conceptual
Overview

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Pacemaker Components
• Non-cluster aware components (illustrated in
green). These pieces include the resources
themselves, scripts that start, stop and monitor
them
• Cluster Resource manager, provides the brain
that processes and reacts to events regarding
the cluster
• Low level infrastructure, Corosync provides
reliable messaging, membership and quorum
information about the cluster

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Pacemaker Stack
• pacemaker corosync cluster called as pacemaker stack
• Linux kernel by default comes with DLM (distributed
lock manager). It provides locking feature which will be
used by cluster aware filesystem
• The GFS2 (Global File System2) and OCFS2 (Oracle
cluster File System 2) are called as cluster aware
filesystem
• To access single filesytem by multiple hosts you need to
have either GFS2 or OCFS2.
• Or you can create a file system on top of cLVM (cluster
logical volume manager)

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Cluster Filesystem
• If you have shared disk and want several nodes access
it, you need cluster aware filesystem
• The open source solution are GFS2 (Global File System2)
and OCFS2 (Oracle cluster File System 2)

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Cluster Block Device
• DRBD (distributed replicated block device) allows you
to create a mirror of two block devices that are
located at two different sites across an IP network.
When used with Corosync, DRBD supports
distributed high-availability Linux clusters. It is a
network based raid1, and high performance data
replication over network
• CLVM2, see https://www.sourceware.org/lvm2/
• Cluster md raid1, see
https://www.kernel.org/doc/Documentation/md-clust
er.txt

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Cluster Block Device

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STONITH
• STONITH is an acronym for “Shoot-The-Other-Node-In-
The-Head”.
• It protects your data from being corrupted by rogue
nodes or concurrent access.
• Just because a node is unresponsive, this doesn’t mean
it isn’t accessing your data. The only way to be 100%
sure that your data is safe, is to use STONITH so we can
be certain that the node is truly offline, before allowing
the data to be accessed from another node.
• STONITH also has a role to play in the event that a
clustered service cannot be stopped. In this case, the
cluster uses STONITH to force the whole node offline,
thereby making it safe to start the service elsewhere.

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Split brain – the HA problem
• Two nodes run the same service, break the
data integrity
• Solution:
‒ Quorum
If cluster doesn’t have quorum no action will be
taken, means fencing and resource management are
disabled without quorum
‒ STONITH
Shoot the other node in the head
• More on stonith http://ourobengr.com/ha/

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Reference
• SUSE HA Extension Doc (can be use for openSUSE
also)
https://www.suse.com/documentation/sle-ha-12/
• HA clusterlabs http://clusterlabs.org
• Corosync doc
http://landley.net/kdocs/ols/2008/ols2008v1-pages
-85-100.pdf
• DRBD http://drbd.linbit.org/en/
• OCFS2 https://ocfs2.wiki.kernel.org/
• CLVM2 https://sourceware.org/lvm2/
• Linux SCSI http://linux-iscsi.org/

35. Case Study / Hands-on

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Setting up HA on Leap
• Scenario:
‒ setting up openSUSE Leap 42.1 as host
‒ create 2 VM with QEMU/KVM, install openSUSE Leap
42.1, configure the network, and all the required
packages
‒ Configure pacemaker corosync drbd
‒ Setup HA webserver

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Preparation
• Install openSUSE Leap 42.1
• Configure all repository
• Install all the required software
• Create at least 2 virtul machine with QEMU/KVM
• Configure the Cluster
• Create DRBD
• Activate web server / nginx or apache
• Test the status

38. Thank you.
Join the conversation,
contribute & have a lot of fun!
www.opensuse.org

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Have a Lot of Fun, and Join Us At:
www.opensuse.org