High availability is a basic requirement for the IT department nowadays. The best known solution in this area is Linux-HA. The first verison dates back to 1998, the second version evolved 2005 but prooved to be a temporary solution. In 2007 it was replaced by a collection of other programs. The evolution of the software might be difficult to understand for a beginner. This talk tries to bring order into the several names of the programs, explains the setup of such clusters and tries to take a glance into the not too far future of the software.

1. (c) Michael Schwartzkopff, 2010 1 / 21
Quo vadis Linux-HA?
Developments in Linux
Clustersoftware
Michael Schwartzkopff
misch@schwartzkopff.org

2. (c) Michael Schwartzkopff, 2010 2 / 21
Background

3. (c) Michael Schwartzkopff, 2010 3 / 21
Linux Clustersoftware
 Linux Virtual Server
 Scales nicely...
 … but is not high available.
 Linux-HA
 Offers high availability ...
 … but does not scale.
 Code is not maintained any more.
 Is beeing replaced by a collection of other
programs.

4. (c) Michael Schwartzkopff, 2010 4 / 21
Linux-HA Version 1 (heartbeat)
 Two servers exchange heartbeats.
 If the standby server does not receive
heartbeats from the active node any more it
starts the services.
 Configuration in a plain text file haresources.
 Cons:
 No monitoring of the services.
 No management of the resources.

5. (c) Michael Schwartzkopff, 2010 5 / 21
Linux-HA Version 2 (CRM)
 Mangement of the resources by a
Cluster Resource Manager (CRM):
 Aktive monitoring of the reosurces by the cluster
software.
 Up to 16 nodes in a cluster.
 Resources free moveable between the nodes.
 Communication in the cluster via heartbeat.
 Constraints determine which resource should run
on what node.

6. (c) Michael Schwartzkopff, 2010 6 / 21
Constraints in Linux-HAv2
 Order
A resource should start before or after an other
resource.
 Colocation
A resource should run on the same node as an
other resource.
 Location
A resource should run on a node with specific
attributes.

7. (c) Michael Schwartzkopff, 2010 7 / 21
Features of Linux-HAv2?
 Pros
 Monitoring of the resources.
 Cons
 Configuration in XML.
 Administration via the command line.
 GUI not really usable.
 Not maintained any more after 2007 (version 2.1.4).

8. (c) Michael Schwartzkopff, 2010 8 / 21
Linux-HA
Managment
Utilities
Communication
Linux-HAv1 Linux-HAv2
heartbeat heartbeat
CRM

9. (c) Michael Schwartzkopff, 2010 9 / 21
Restart
 If the CRM uses heartbeat only for the
communicaton in the cluster, this could be done
also by another program.
 The other software was OpenAIS.
 The developers organized the CRM code in a
separate project called pacemaker. It uses
either heartbeat or OpenAIS.
 Some utilities from the heartbeat-package
were still nescessary.

10. (c) Michael Schwartzkopff, 2010 10 / 21
pacemaker
Managment
Utilities
Communication
Linux-HAv1 Linux-HAv2 pacemaker
heartbeat heartbeat
CRM
heart-
beat
pacemaker
OpenAIS

11. (c) Michael Schwartzkopff, 2010 11 / 21
pacemaker
 Uses heartbeat or OpenAIS.
 Suitable GUI.
 Own subshell additional to the CLI.
 Sanboxes for testing.
 First test what would happen, if ...
→ only afterwards activate the new configuration.
 Exact history, what happened why.

12. (c) Michael Schwartzkopff, 2010 12 / 21
pacemaker: The GUI

13. (c) Michael Schwartzkopff, 2010 13 / 21
Sandboxes with graphics!

14. (c) Michael Schwartzkopff, 2010 14 / 21
The development goes on
 OpenAIS offers much more as needed by
pacemaker. The communication stack is
forked into a separate project called corosync.
 corosync is responsible for the
communication in the cluster.
 OpenAIS takes care for all ”higher” services in
a cluster.
 Simple clusters with pacemaker only need
corosync.

15. (c) Michael Schwartzkopff, 2010 15 / 21
Decomposition of heartbeat
 With pacemaker 1.0.5, heartbeat is
decomposed into three projects:
 cluster-glue includes all nescessary utilities.
 The resource-agents combines all resource
agents, the interfaces between pacemaker and the
application's binaries.
 In heartbeat (version ≥ 3.0.2) remains, what is
left from the project.

16. (c) Michael Schwartzkopff, 2010 16 / 21
HA-cluster with Linux
Management
Utilities
Communi-
cation
Linux-HAv1 Linux-HAv2 pacemaker pacemaker ≥ 1.0.5
heartbeat heartbeat
CRM
heart-
beat
pacemaker
OpenAIS
pacemaker
heart-
beat
coro-
sync
cluster-glue
resource-
agents

17. (c) Michael Schwartzkopff, 2010 17 / 21
Problem: Shared Data
 Many cluster applications need to access
shared data (data bases, ..)
 A locking mechanism, that guarantees
exclusive write access in inevitable.
 Locking included in NFS.
 Concurrent access nescessary?
 Ordinary filesystem or ...
 … or cluster filesystem.

18. (c) Michael Schwartzkopff, 2010 18 / 21
Filesystems in a cluster
 Cluster filesystems need a distributed locking
mechanism.
 dlm2 offers this serivce.
 dlm2 needs the ”higher” services of OpenAIS.
 With dlm2 cluster filesystems are possible:
 Oracle Cluster Filesystem (OCFS2)
 Red Hats Global Filesystem (GFS)
 Clustering extensions to LVM2 (cLVM)

19. (c) Michael Schwartzkopff, 2010 19 / 21
Filesystems in a cluster (II)
OpenAISpacemaker
corosynccluster-glue
resource-
agents
OCFS2
DLM2
GFSFilesystems
Distributed Locking
cLVM
Management
Communication /
Utilities

20. (c) Michael Schwartzkopff, 2010 20 / 21
Roadmap
 Java – based GUI of Linbit.
 Configuration of storage media incl. DRBD.
 Configuration of virtual machines.
 Role model for the administration.
 Distribution of the resources accoring to
nescessary capacities.
 Rewriting of the system health.

21. (c) Michael Schwartzkopff, 2010 21 / 21
Thank you very much for your attention!
Questions?