Installation and Setup Quick Start #
This document guides you through the setup of a very basic two-node cluster,
using the bootstrap scripts provided by the
ha-cluster-bootstrap
package.
This includes the configuration of a virtual IP address as a cluster
resource and the use of SBD on shared storage as fencing mechanism.
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1 Usage Scenario #
The procedures in this document will lead to a minimal setup of a two-node cluster with the following properties:
Two nodes:
alice
(IP:192.168.1.1
) andbob
(IP:192.168.1.2
), connected to each other via network.A floating, virtual IP address (
192.168.1.1
) which allows clients to connect to the service no matter which physical node it is running on.A shared storage device, used as SBD fencing mechanism. This avoids split brain scenarios.
Failover of resources from one node to the other if the active host breaks down (active/passive setup).
After setup of the cluster with the bootstrap scripts, we will monitor the cluster with the graphical HA Web Console (Hawk), one of the cluster management tools included with SUSE® Linux Enterprise High Availability. As a basic test of whether failover of resources works, we will put one of the nodes into standby mode and check if the virtual IP address is migrated to the second node.
You can use the two-node cluster for testing purposes or as a minimal cluster configuration that you can extend later on. Before using the cluster in a production environment, modify it according to your requirements.
2 System Requirements #
This section informs you about the key system requirements for the scenario described in Section 1, “Usage Scenario”. If you want to adjust the cluster for use in a production environment, read the full list of System Requirements and Recommendations in Book “Administration Guide”, Chapter 2 “System Requirements and Recommendations”.
- Servers
Two servers with software as specified in Software Requirements.
The servers can be bare metal or virtual machines. They do not require identical hardware (memory, disk space, etc.), but they must have the same architecture. Cross-platform clusters are not supported.
- Communication Channels
At least two TCP/IP communication media per cluster node. The network equipment must support the communication means you want to use for cluster communication: multicast or unicast. The communication media should support a data rate of 100 Mbit/s or higher. For a supported cluster setup two or more redundant communication paths are required. This can be done via:
Network Device Bonding (to be preferred).
A second communication channel in Corosync.
Network fault tolerance on infrastructure layer (for example, hypervisor).
- Node Fencing/STONITH
To avoid a “split brain” scenario, clusters need a node fencing mechanism. In a split brain scenario, cluster nodes are divided into two or more groups that do not know about each other (because of a hardware or software failure or because of a cut network connection). A fencing mechanism isolates the node in question (usually by resetting or powering off the node). This is also called STONITH (“Shoot the other node in the head”). A node fencing mechanism can be either a physical device (a power switch) or a mechanism like SBD (STONITH by disk) in combination with a watchdog. Using SBD requires shared storage.
On all nodes that will be part of the cluster the following software must be installed:
SUSE® Linux Enterprise Server 12 SP5 (with all available online updates)
SUSE Linux Enterprise High Availability 12 SP5 (with all available online updates)
- Time Synchronization
Cluster nodes must synchronize to an NTP server outside the cluster. For more information, see https://documentation.suse.com/sles-12/html/SLES-all/cha-netz-xntp.html.
The cluster might not work properly if the nodes are not synchronized, or even if they are synchronized but have different timezones configured. In addition, log files and cluster reports are very hard to analyze without synchronization. If you use the bootstrap scripts, you will be warned if NTP is not configured yet.
- Host Name and IP Address
Use static IP addresses.
List all cluster nodes in the
/etc/hosts
file with their fully qualified host name and short host name. It is essential that members of the cluster can find each other by name. If the names are not available, internal cluster communication will fail.
- SSH
All cluster nodes must be able to access each other via SSH. Tools like
crm report
(for troubleshooting) and Hawk2's require passwordless SSH access between the nodes, otherwise they can only collect data from the current node.If you use the bootstrap scripts for setting up the cluster, the SSH keys will automatically be created and copied.
3 Overview of the Bootstrap Scripts #
All commands from the ha-cluster-bootstrap package execute bootstrap scripts that require only a minimum of time and manual intervention.
With
ha-cluster-init
, define the basic parameters needed for cluster communication. This leaves you with a running one-node cluster.With
ha-cluster-join
, add more nodes to your cluster.With
ha-cluster-remove
, remove nodes from your cluster.
All bootstrap scripts log to /var/log/ha-cluster-bootstrap.log
.
Check this file for any details of the bootstrap process. Any options set
during the bootstrap process can be modified later with the
YaST cluster module. See Book “Administration Guide”, Chapter 3 “Installing SUSE Linux Enterprise High Availability”, Section 3.1 “Manual Installation”
for details.
Each script comes with a man page covering the range of functions, the script's options, and an overview of the files the script can create and modify.
The bootstrap script ha-cluster-init
checks and
configures the following components:
- NTP
If NTP has not been configured to start at boot time, a message appears.
- SSH
It creates SSH keys for passwordless login between cluster nodes.
- Csync2
It configures Csync2 to replicate configuration files across all nodes in a cluster.
- Corosync
It configures the cluster communication system.
- SBD/Watchdog
It checks if a watchdog exists and asks you whether to configure SBD as node fencing mechanism.
- Virtual Floating IP
It asks you whether to configure a virtual IP address for cluster administration with Hawk2.
- Firewall
It opens the ports in the firewall that are needed for cluster communication.
- Cluster Name
It defines a name for the cluster, by default
clusterNUMBER
. This is optional and mostly useful for Geo clusters. Usually, the cluster name reflects the location and makes it easier to distinguish a site inside a Geo cluster.
4 Installing SUSE Linux Enterprise Server and High Availability Extension #
The packages for configuring and managing a cluster with SUSE Linux Enterprise High Availability
are included in the High Availability
installation
pattern. This pattern is only available after SUSE Linux Enterprise High Availability has been
installed as an extension to SUSE® Linux Enterprise Server.
For information on how to install extensions, see the Deployment Guide for SUSE Linux Enterprise Server 12 SP5.
If the pattern is not installed yet, install it with the command
zypper install -t pattern ha_sles
.
Alternatively, install the pattern with YaST. Proceed as follows:
Start YaST and select
› .Click the
tab and activate the pattern in the pattern list.Click
to start installing the packages.Install the High Availability pattern on all machines that will be part of your cluster.
Note: Installing Software Packages on All PartiesFor an automated installation of SUSE Linux Enterprise Server 12 SP5 and SUSE Linux Enterprise High Availability 12 SP5, use AutoYaST to clone existing nodes. For more information, see Book “Administration Guide”, Chapter 3 “Installing SUSE Linux Enterprise High Availability”, Section 3.2 “Mass Installation and Deployment with AutoYaST”.
Register the machines at SUSE Customer Center. Find more information in the Upgrade Guide for SUSE Linux Enterprise Server 12 SP5.
5 Using SBD as Fencing Mechanism #
If you have shared storage, for example, a SAN (Storage Area Network),
you can use it to avoid split brain scenarios by configuring SBD
as node fencing mechanism. SBD uses watchdog support
and the external/sbd
STONITH resource agent.
5.1 Requirements for SBD #
During setup of the first node with ha-cluster-init
, you
can decide whether to use SBD. If yes, you need to enter the path to the shared
storage device. By default, ha-cluster-init
will automatically
create a small partition on the device to be used for SBD.
To use SBD, the following requirements must be met:
The path to the shared storage device must be persistent and consistent across all nodes in the cluster. Use stable device names such as
/dev/disk/by-id/dm-uuid-part1-mpath-abcedf12345
.The SBD device must not use host-based RAID, cLVM2, nor reside on a DRBD* instance.
For details of how to set up shared storage, refer to the Storage Administration Guide for SUSE Linux Enterprise Server 12 SP5.
5.2 Setting Up Softdog Watchdog and SBD #
In SUSE Linux Enterprise Server, watchdog support in the kernel is enabled by default: It ships with several kernel modules that provide hardware-specific watchdog drivers. SUSE Linux Enterprise High Availability uses the SBD daemon as the software component that “feeds” the watchdog.
The following procedure uses the softdog
watchdog.
The softdog driver assumes that at least one CPU is still running. If all CPUs are stuck, the code in the softdog driver that should reboot the system will never be executed. In contrast, hardware watchdogs keep working even if all CPUs are stuck.
Before using the cluster in a production environment, it is highly
recommended to replace the softdog
module with the
respective hardware module that best fits your hardware.
However, if no watchdog matches your hardware,
softdog
can be used as kernel
watchdog module.
Create a persistent, shared storage as described in Section 5.1, “Requirements for SBD”.
Enable the softdog watchdog:
#
echo
softdog > /etc/modules-load.d/watchdog.conf#
systemctl
restart systemd-modules-loadTest if the softdog module is loaded correctly:
#
lsmod
| egrep "(wd|dog)" softdog 16384 1On
bob
, initialize the SBD partition:#
sbd
-d /dev/SBDDEVICE createStart SBD to listen on the SBD device:
#
sbd
-d /dev/SBDDEVICE watchOn
alice
, send a test message:#
sbd
-d /dev/SBDDEVICE message bob testOn
bob
, check the status withsystemctl
and you should see the received message:#
systemctl
status sbd [...] info: Received command test from alice on disk SBDDEVICEStop watching the SBD device on
bob
with:#
systemctl
stop sbd
Testing the SBD fencing mechanism for proper function in case of a split brain situation is highly recommended. Such a test can be done by blocking the Corosync cluster communication.
6 Setting Up the First Node #
Set up the first node with the ha-cluster-init
script.
This requires only a minimum of time and manual intervention.
alice
) with
ha-cluster-init
#Log in as
root
to the physical or virtual machine you want to use as cluster node.Start the bootstrap script by executing:
#
ha-cluster-init
--name CLUSTERNAMEReplace the CLUSTERNAME placeholder with a meaningful name, like the geographical location of your cluster (for example,
amsterdam
). This is especially helpful if you want to create a Geo cluster later on, as it simplifies the identification of a site. If you run the command without the--name
option, the default name ishacluster
.If you need unicast instead of multicast (the default) for your cluster communication, use the option
-u
. After installation, find the valueudpu
in the file/etc/corosync/corosync.conf
. Ifha-cluster-init
detects a node running on Amazon Web Services (AWS), the script will use unicast automatically as default for cluster communication.The scripts checks for NTP configuration and a hardware watchdog service. It generates the public and private SSH keys used for SSH access and Csync2 synchronization and starts the respective services.
Configure the cluster communication layer (Corosync):
Enter a network address to bind to. By default, the script will propose the network address of
eth0
. Alternatively, enter a different network address, for example the address ofbond0
.Enter a multicast address. The script proposes a random address that you can use as default. Of course, your particular network needs to support this multicast address.
Enter a multicast port. The script proposes
5405
as default.
Finally, the script will start the Pacemaker service to bring the one-node cluster online and enable Hawk2. The URL to use for Hawk2 is displayed on the screen.
Set up SBD as node fencing mechanism:
Confirm with
y
that you want to use SBD.Enter a persistent path to the partition of your block device that you want to use for SBD, see Section 5, “Using SBD as Fencing Mechanism”. The path must be consistent across all nodes in the cluster.
Configure a virtual IP address for cluster administration with Hawk2. (We will use this virtual IP resource for testing successful failover later on).
Confirm with
y
that you want to configure a virtual IP address.Enter an unused IP address that you want to use as administration IP for Hawk2:
192.168.1.1
Instead of logging in to an individual cluster node with Hawk2, you can connect to the virtual IP address.
You now have a running one-node cluster. To view its status, proceed as follows:
On any machine, start a Web browser and make sure that JavaScript and cookies are enabled.
As URL, enter the IP address or host name of any cluster node running the Hawk Web service. Alternatively, enter the address of the virtual IP address that you configured in Step 6 of Procedure 2, “Setting Up the First Node (
alice
) withha-cluster-init
”:https://HAWKSERVER:7630/
Note: Certificate WarningIf a certificate warning appears when you try to access the URL for the first time, a self-signed certificate is in use. Self-signed certificates are not considered trustworthy by default.
Ask your cluster operator for the certificate details to verify the certificate.
To proceed anyway, you can add an exception in the browser to bypass the warning.
On the Hawk2 login screen, enter the
and of the user that has been created during the bootstrap procedure (userhacluster
, passwordlinux
).Important: Secure PasswordReplace the default password with a secure one as soon as possible:
#
passwd
haclusterClick
. After login, the Hawk2 Web interface shows the Status screen by default, displaying the current cluster status at a glance:Figure 1: Status of the One-Node Cluster in Hawk2 #
7 Adding the Second Node #
If you have a one-node cluster up and running, add the second cluster
node with the ha-cluster-join
bootstrap
script, as described in Procedure 4.
The script only needs access to an existing cluster node and
will complete the basic setup on the current machine automatically.
For details, refer to the ha-cluster-join
man page.
The bootstrap scripts take care of changing the configuration specific to a two-node cluster, for example, SBD and Corosync.
bob
) with
ha-cluster-join
#Log in as
root
to the physical or virtual machine supposed to join the cluster.Start the bootstrap script by executing:
#
ha-cluster-join
If NTP has not been configured to start at boot time, a message appears. The script also checks for a hardware watchdog device (which is important in case you want to configure SBD) and warns you if none is present.
If you decide to continue anyway, you will be prompted for the IP address of an existing node. Enter the IP address of the first node (
alice
,192.168.1.1
).If you have not already configured a passwordless SSH access between both machines, you will also be prompted for the
root
password of the existing node.After logging in to the specified node, the script will copy the Corosync configuration, configure SSH and Csync2, and will bring the current machine online as new cluster node. Apart from that, it will start the service needed for Hawk2.
Check the cluster status in Hawk2. Under Figure 2, “Status of the Two-Node Cluster”).
› you should see two nodes with a green status (see8 Testing the Cluster #
Section 8.1, “Testing Resource Failover” is a simple test to check if the
cluster moves the virtual IP address to the other node if the node
that currently runs the resource is set to standby
.
However, a realistic test involves specific use cases and scenarios, including testing of your fencing mechanism to avoid a split brain situation. If you have not set up your fencing mechanism correctly, the cluster will not work properly.
Before using the cluster in a production environment, test it thoroughly
according to your use cases or by using the crm cluster crash_test
command.
8.1 Testing Resource Failover #
As a quick test, the following procedure checks on resource failovers:
Open a terminal and ping
192.168.1.1
, your virtual IP address:#
ping
192.168.1.1Log in to your cluster as described in Procedure 3, “Logging In to the Hawk2 Web Interface”.
In Hawk2
› , check which node the virtual IP address (resourceadmin_addr
) is running on. We assume the resource is running onalice
.Put
alice
into mode (see Figure 3, “Nodealice
in Standby Mode”).Figure 3: Nodealice
in Standby Mode #Click
› . The resourceadmin_addr
has been migrated tobob
.
During the migration, you should see an uninterrupted flow of pings to
the virtual IP address. This shows that the cluster setup and the floating
IP work correctly. Cancel the ping
command with
Ctrl–C.
8.2 Testing with the crm cluster crash_test
command #
The command crm cluster crash_test
triggers cluster failures to find
problems. Before you use your cluster in production, it is
recommended to use this command to make sure everything works as expected.
The command supports the following checks:
--split-brain-iptables
Simulates a split brain scenario by blocking the Corosync port. Checks whether one node can be fenced as expected.
--kill-sbd
/--kill-corosync
/--kill-pacemakerd
Kills the daemons for SBD, Corosync, and Pacemaker. After running one of these tests, you can find a report in the directory
/var/lib/crmsh/crash_test/
. The report includes a test case description, action logging, and an explanation of possible results.--fence-node NODE
Fences a specific node passed from the command line.
For more information, see crm cluster crash_test --help
.
#
crm_mon -1
Stack: corosync Current DC: alice (version ...) - partition with quorum Last updated: Fri Mar 03 14:40:21 2020 Last change: Fri Mar 03 14:35:07 2020 by root via cibadmin on alice 2 nodes configured 1 resource configured Online: [ alice bob ] Active resources: stonith-sbd (stonith:external/sbd): Started alice#
crm cluster crash_test
--fence-node bob ============================================== Testcase: Fence node bob Fence action: reboot Fence timeout: 60 !!! WARNING WARNING WARNING !!! THIS CASE MAY LEAD TO NODE BE FENCED. TYPE Yes TO CONTINUE, OTHER INPUTS WILL CANCEL THIS CASE [Yes/No](No):Yes
INFO: Trying to fence node "bob" INFO: Waiting 60s for node "bob" reboot... INFO: Node "bob" will be fenced by "alice"! INFO: Node "bob" was successfully fenced by "alice"
To watch bob
change status during
the test, log in to Hawk2 and navigate to › .
9 For More Information #
Find more documentation for this product at https://documentation.suse.com/sle-ha-12. The documentation also includes a comprehensive Administration Guide for SUSE Linux Enterprise High Availability. Refer to it for further configuration and administration tasks.
A GNU licenses #
This appendix contains the GNU Free Documentation License version 1.2.
GNU Free Documentation License #
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5. COMBINING DOCUMENTS #
You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.
The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.
In the combination, you must combine any sections Entitled "History" in the various original documents, forming one section Entitled "History"; likewise combine any sections Entitled "Acknowledgements", and any sections Entitled "Dedications". You must delete all sections Entitled "Endorsements".
6. COLLECTIONS OF DOCUMENTS #
You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.
You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.
7. AGGREGATION WITH INDEPENDENT WORKS #
A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an "aggregate" if the copyright resulting from the compilation is not used to limit the legal rights of the compilation's users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document's Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.
8. TRANSLATION #
Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.
If a section in the Document is Entitled "Acknowledgements", "Dedications", or "History", the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.
9. TERMINATION #
You may not copy, modify, sublicense, or distribute the Document except as expressly provided for under this License. Any other attempt to copy, modify, sublicense or distribute the Document is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.
10. FUTURE REVISIONS OF THIS LICENSE #
The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See https://www.gnu.org/copyleft/.
Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License "or any later version" applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation.
ADDENDUM: How to use this License for your documents #
Copyright (c) YEAR YOUR NAME. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License”.
If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with...Texts.” line with this:
with the Invariant Sections being LIST THEIR TITLES, with the Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.
If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.
If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.