Linux: The Simplest Load Balancing Cluster with Failover

Evidian SafeKit

How the Evidian SafeKit software simply implements Linux load balancing and failover without network load balancers or dedicated proxy servers

How the Evidian SafeKit farm cluster implements Linux load balancing and failover?

Evidian SafeKit brings load balancing and failover to Linux. This article explains how to implement quickly a Linux cluster without network load balancers or dedicated proxy servers. SafeKit is installed directly on the Linux servers. The high availabity module farm.safe and a free trial are offered in the Installation tab below.

Note that SafeKit is a generic product. You can implement with the same product real-time replication and failover of directories and services, databases, docker containers, full Hyper-V or KVM virtual machines, Cloud applications. See other examples of mirror modules here.

This clustering solution is recognized as the simplest to implement by our customers and partners. It is also a complete solution that solves

  • hardware failures (20% of problems), including the complete failure of a computer room,
  • software failures (40% of problems), including smooth upgrade server by server,
  • and human errors (40% of problems) thanks to its ease of use, including a very simple administration web console to configure, control and monitor clusters.

On the previous figure, Linux services are running of the 3 servers. Users are connected to a virtual IP address which is configured locally on each server. The input traffic for the virtual IP address is received by all the servers and split among them by a filter inside each server's kernel.

The network load balancing algorithm inside the filter is based on the identity of the client packets (client IP address, client TCP port). Depending on the identity of the client packet input, only one filter in a server accepts the packet; the other filters in other servers reject it.

Once a packet is accepted by the filter on a server, only the CPU and memory of this server are used by Linux services that responds to the request of the client. The output messages are sent directly from the Linux server to the client.

If a server fails, the SafeKit membership protocol reconfigures the filters in the network load balancing cluster to re-balance the traffic on the remaining available servers.

Note that that you can deploy several modules on the same cluster. Each module will have its own virtual IP address. For example, you can implement a mixed of farm and mirror modules.

Free trial + farm.safe module and step by step installation procedure of SafeKit load balancing on several Linux servers

Installation of a SafeKit / Linux load balancing cluster with failover

Prerequisites

  • you need the application that you want to put in farme installed on 2 nodes or more (virtual machines or physical servers)

Package installation on Linux

  • Install the free version of SafeKit on 2 Linux nodes (or more)
  • After the download of safekit_xx.bin package, execute it to extract the rpm and the safekitinstall script and then execute the safekitinstall script
  • Answer yes to firewall automatic configuration
  • The module farm.safe is delivered inside the package.

Note   User's guide available here

Go to the Configuration tab

Configuration of a SafeKit / Linux load balancing cluster with failover

Configuration instructions

The configuration is presented with 2 nodes but it can be made with more than 2 nodes.

Warning  Important: all the configuration is made from a single browser.

Launch the web console in a browser on one node by connecting to http://localhost:9010 (next image). You can also run the console in a browser on an external workstation by connecting to the physical IP address of one node.

Start the SafeKit web console for configuring Linux

Note   To secure the web console, see 11. Securing the SafeKit web console in the User's Guide.

Enter IP address of the first node and click on Confirm (next image)

SafeKit web console - first Linux node in the cluster

Click on New node and enter IP address of the second node (next image)
Then click on the red floppy disk to save the configuration (next image)

SafeKit web console - second Linux node in the cluster

Note   In the previous image, the save operation put the IP addresses in the file /var/safekit/cluster/cluster.xml and apply the distributed command /opt/safekit/safekit –H "*" -G which configures node 1 and node 2. So do not redo this operation on the other node. Check the connectivity and firewall between both nodes for troubleshooting.

In the Configuration tab, click on farm.safe (xxx.safe in the next image) then  enter farm as the module name and Confirm (the console finds farm.safe in the demo/ directory that you previously filled in the Installation tab)

SafeKit web console - start configuration of Linux SafeKit web console - enter Linux module name

Click on Validate (next image)

SafeKit web console - enter Linux module nodes

Set the virtual IP address of the cluster, the TCP port of the service to load balance and the criterion on source IP address or source TCP port (next image).

A virtual IP address is a new unused IP address in the same IP network (same subnet) as the IP addresses of the two nodes. The load balancing will be made on the virtual IP address/TCP port according the criterion. This article explains difference between source IP address and source TCP port.

SafeKit web console - enter Linux parameters

For information:

  • on the previous image, if a proc process is defined in the Process checker section, it will be monitored with the action restart in case of failure. The services will be stopped an restarted locally on the local server if this process disappears from the list of running processes. After 3 unsuccessful local restarts, the module is stopped on the local server and the load balancing filters are reconfigured to load balance the traffic on the remaining servers of the farm.
  • start_both and stop_both (previous image) contain the start and the stop of Linux services. Check that the names of services in these scripts are those installed on your both machines (else modify them in the scripts).

Click on Validate (previous image)

SafeKit web console - stop the Linux module before configuration

Click on Configure (previous image)

SafeKit web console - check the success green messages of the Linux configuration

Check the success green message on both servers and click on Next (previous image)

SafeKit web console - start the Linux cluster on both nodes

Start the cluster on both nodes (previous image). Check that the status becomes UP (green) - UP (green) (next image).

SafeKit web console - Linux cluster started

The cluster is operational with Linux services running on both UP nodes (previous image).

Be careful, components which are clients of the Linux services must be configured with the virtual IP address. The configuration can be made with a DNS name (if a DNS name has been created and associated with the virtual IP address).

Tests

Check with Linux command lines that the Linux services have been started by start_both on both UP nodes. Put Linux services with Boot Startup Type = Manual (SafeKit controls start of Linux services).

Stop one UP node by scrolling down the menu of the node and by clicking on Stop. Check that the load balancing is reconfigured with only the other node taking all TCP connections. And check with Linux command lines that the Linux services have been stopped by stop_both on the STOP node.

More information on tests in the User's Guide

Automatic start of the module at boot

Configure boot start (next image on the right side) configures the automatic boot of the module when the server boots. Do this configuration on both nodes once the Linux load balancing and failover solution is correctly running.

SafeKit web console - automatic boot of the Linux module

For reading the SafeKit logs, go to the Troubleshooting tab

For editing userconfig.xml, start_both and stop_both, go to the Advanced Configuration tab

Troubleshooting of a SafeKit / Linux load balancing cluster with failover

Module log

Read the module log to understand the reasons of a failover, of a waiting state on the availability of a resource etc...
To see the module log of node 1 (next image):

  • click on the Control tab
  • click on node 1/UP (it becomes blue) on the left side
  • click on Module Log
  • click on the Refresh icon (green arrows) to update the console
  • click on the floppy disk to save the module log in a .txt file and to analyze in a text editor

Repeat the same operation to see the module log of node 2.

SafeKit web console - Module Log of the Linux node 1

Application log

Read the application log to see the output messages of the stat_both and stop_both restart scripts.
To see the application log of node 1 (next image):

  • click on the Control tab
  • click on node 1/UP (it becomes blue) on the left side to select the server
  • click on Application Log to see messages when starting and stopping Linux services
  • click on the Refresh icon (green arrows) to update the console
  • click on the floppy disk to save the application log in a .txt file and to analyze in a text editor

Repeat the same operation to see the application log of node 2.

SafeKit web console - Application Log of Linux node 1

More information on troubleshooting in the User's Guide

For support, go to the Support tab

Advanced configuration of a SafeKit / Linux load balancing cluster with failover

Advanced configuration

In Advanced Configuration tab (next image), you can edit internal files of the module: bin/start_both and bin/stop_both and conf/userconfig.xml (next image on the left side). If you make change in the internal files here, you must apply the new configuration by a right click on the blue icon/xxx on the left side (next image): the interface will allow you to redeploy the modified files on both servers.

SafeKit web console - Advanced configuration of the Linux module

More information on userconfig.xml in the User's Guide

For an example of userconfig.xml, start_both and stop_both, go to the Internals tab

Support of a SafeKit / Linux load balancing cluster with failover

Support

For getting support on the call desk of https://support.evidian.com, get 2 Snaphots (2 .zip files), one for each server and upload them in the call desk tool (next image).

SafeKit web console - Linux snaphots for support

More information on support in the User's Guide

Internal files of a SafeKit / Linux load balancing cluster with failover

Go to the Advanced Configuration tab, for editing these files

Internal files of the Linux farm.safe module

userconfig.xml (description in the User's Guide)
<!DOCTYPE safe>
<safe>
<service mode="farm" maxloop="3" loop_interval="24">
  <!-- Farm topology configuration for the membership protocol -->
  <!-- Names or IP addresses on the default network are set during initialization in the console -->
  <farm>
    <lan name="default" />
  </farm>
  <!-- Virtual IP Configuration -->
  <!-- Replace
     * VIRTUAL_IP_ADDR_TO_BE_DEFINED by the IP address of your virtual server 
  -->
  <vip>
    <interface_list>
      <interface check="on" arpreroute="on">
        <virtual_interface type="vmac_directed">
          <virtual_addr addr="VIRTUAL_IP_ADDR_TO_BE_DEFINED" where="alias"/>
        </virtual_interface>
      </interface>
    </interface_list>
    <loadbalancing_list>
      <group name="Windows_Appli">
        <!-- Set load-balancing rule on the TCP port of the service to load balance -->
        <rule port="TCP_PORT_TO_BE_DEFINED" proto="tcp" filter="on_addr"/>
      </group>
    </loadbalancing_list>
  </vip>
  <!-- TCP Checker Configuration -->
  <!-- Replace
     * VIRTUAL_IP_ADDR_TO_BE_DEFINED by the IP address of your virtual server 
     * TCP_PORT_TO_BE_DEFINED by the TCP port of the service to check
  -->
  <check>
    <tcp ident="Check_Appli" when="both">
      <to
         addr="VIRTUAL_IP_ADDR_TO_BE_DEFINED"
         port="TCP_PORT_TO_BE_DEFINED"
         interval="10"
         timeout="5"
       />
    </tcp>
  </check>
  <!-- User scripts activation -->
  <user nicestoptimeout="300" forcestoptimeout="300" logging="userlog" />
</service>
</safe>
start_both
#!/bin/sh
# Script called on the primary server for starting application

# For logging into SafeKit log use:
# $SAFE/safekit printi | printe "message" 

# stdout goes into Application log
echo "Running start_both $*" 

res=0

# Fill with your application start call

if [ $res -ne 0 ] ; then
  $SAFE/safekit printe "start_both failed"

  # uncomment to stop SafeKit when critical
  # $SAFE/safekit stop -i "start_both"
fi
stop_both
#!/bin/sh
# Script called on the primary server for stopping application

# For logging into SafeKit log use:
# $SAFE/safekit printi | printe "message" 

#----------------------------------------------------------
#
# 2 stop modes:
#
# - graceful stop
#   call standard application stop
#
# - force stop ($1=force)
#   kill application's processes
#
#----------------------------------------------------------

# stdout goes into Application log
echo "Running stop_both $*" 

res=0

# default: no action on forcestop
[ "$1" = "force" ] && exit 0

# Fill with your application stop call

[ $res -ne 0 ] && $SAFE/safekit printe "stop_both failed"

Customers of SafeKit High Availability Software in all Business Activities

  • Best high availability use cases with SafeKit

    Best use cases [+]

    Like   OEM Software Like   Distributed Enterprise Like   Remote Sites
    Application Clustering Software for a Software Publisher High Availability Software in a Distributed Enterprise Business Continuity and Disaster Recovery without a replicated SAN
    A software publisher uses SafeKit as an OEM software for high availability of its application A distributed enterprise deploys SafeKit in many branches without specific IT skills SafeKit is deployed in two remote sites without the need for replicated bays of disks through a SAN

    Testimonials

    Like  The ideal product for a software publisher

    “SafeKit is the ideal application clustering solution for a software publisher. We currently have deployed more than 80 SafeKit clusters worldwide with our critical TV broadcasting application.

    Like  The product very easy to deploy for a reseller

    “WithNCompany has deployed in South Korea many SafeKit high availability solutions with the Hanwha Video Surveillance Platform. SafeKit is appreciated because the product is easy to install and very quickly deployed.”

    Like  The product to gain time for a system integrator

    “Thanks to a simple and powerful product, we gained time in the integration and validation of our critical projects like the supervision of Paris and Marseille metro lines (the control rooms).”


  • High availability of Video Surveillance Platforms with SafeKit

    Video surveillance and access control [+]

    In video surveillance systems and access control, Evidian SafeKit implements high availability with synchronous replication and failover of

    Sebastien Temoin, Technical and Innovation Director, NOEMIS, value added distributor of Milestone solutions:

    "SafeKit by Evidian is a professional solution making easy the redundancy of Milestone Management Server, Event Server, Log Server. The solution is easy to deploy, easy to maintain and can be added on existing installation. We have assisted integrators to deploy the solution on many projects such as city surveillance, datacenters, stadiums and other critical infrastructures. SafeKit is a great product, and Evidian provides great support. Happy to help if you have any questions."

    Use cases:


  • Harmonic has deployed more than 80 SafeKit clusters for high availability of its TV broadcasting application over satellites, terrestrials, cable, IPTV.

    TV broadcasting [+]

    Harmonic is using SafeKit as a software OEM high availability solution and deploys it with its TV broadcasting solutions over satellites, terrestrials, cable, IPTV.

    Over 80 SafeKit clusters are deployed on Windows for replication of Harmonic database and automatic failover of the critical application.

    Philippe Vidal, Product Manager, Harmonic says:

    “SafeKit is the ideal application clustering solution for a software publisher looking for a simple and economical high availability software. We are deploying SafeKit worldwide and we currently have more than 80 SafeKit clusters on Windows with our critical TV broadcasting application through terrestrial, satellite, cable and IP-TV. SafeKit implements the continuous and real-time replication of our database as well as the automatic failover of our application for software and hardware failures. Without modifying our application, it was possible for us to customize the installation of SafeKit. Since then, the time of preparation and implementation has been significantly reduced.”


  • The European Society of Warranties and Guarantees in Natixis uses SafeKit as a high availability solution for its applications.

    Finance [+]

    The European Society of Warranties and Guarantees in Natixis uses SafeKit as a high availability solution for its applications.

    Over 30 SafeKit clusters are deployed on Unix and Windows in Natixis.


  • Fives Syleps implements high availability of its ERP with SafeKit and deploys the solution in the food industry.

    Industry [+]

    Fives Syleps implements high availability of its ERP with SafeKit and deploys the solution in the food industry.

    Over 20 SafeKit clusters are deployed on Linux and Windows with Oracle.

    Testimonial of Fives Syleps:

    "The automated factories that we equip rely on our ERP. It is not possible that our ERP is out of service due to a computer failure. Otherwise, the whole activity of the factory stops.

    We chose the Evidian SafeKit high availability product because it is an easy to use solution. It is implemented on standard servers and does not require the use of shared disks on a SAN and load balancing network boxes.

    It allows servers to be put in remote computer rooms. In addition, the solution is homogeneous for Linux and Windows platforms. And it provides 3 functionalities: load balancing between servers, automatic failover and real-time data replication.”


  • Air traffic control systems supplier, Copperchase, deploys SafeKit high availability in airports.

    Air traffic control [+]

    Air traffic control systems supplier, Copperchase, deploys SafeKit high availability in airports.

    Over 20 SafeKit clusters are deployed on Windows.

    Tony Myers, Director of Business Development says:

    "By developing applications for air traffic control, Copperchase is in one of the most critical business activities. We absolutely need our applications to be available all the time. We have found with SafeKit a simple and complete clustering solution for our needs. This software combines in a single product load balancing, real time data replication with no data loss and automatic failover. This is why, Copperchase deploys SafeKit for air traffic control in airports in the UK and the 30 countries where we are present."


  • Software vendor Wellington IT deploys SafeKit high availability with its banking application for Credit Unions in Ireland and UK.

    Bank [+]

    Software vendor Wellington IT deploys SafeKit high availability with its banking application for Credit Unions in Ireland and UK.

    Over 25 SafeKit clusters are deployed on Linux with Oracle.

    Peter Knight, Sales Manager says:

    "Business continuity and disaster recovery are a major concern for our Locus banking application deployed in numerous Credit Unions around Ireland and the UK. We have found with SafeKit a simple and robust solution for high availability and synchronous replication between two servers with no data loss. With this software solution, we are not dependent on a specific and costly hardware clustering solution. It is a perfect tool to provide a software high availability option to an application of a software vendor."


  • Paris transport company (RATP) chose the SafeKit high availability and load balancing solution for the centralized control room of line 1 of the Paris subway.

    Transport [+]

    Paris transport company (RATP) chose the SafeKit high availability and load balancing solution for the centralized control room of line 1 of the Paris subway.

    20 SafeKit clusters are deployed on Windows and Linux.

    Stéphane Guilmin, RATP, Project manager says:

    "Automation of line 1 of the Paris subway is a major project for RATP, requiring a centralized command room (CCR) designed to resist IT failures. With SafeKit, we have three distinct advantages to meet this need. Firstly, SafeKit is a purely software solution that does not demand the use of shared disks on a SAN and network boxes for load balancing. It is very simple to separate our servers into separate machine rooms. Moreover, this clustering solution is homogeneous for our Windows and Linuxplatforms. SafeKit provides the three functions that we needed: load balancing between servers, automatic failover after an incident and real time data replication."

    And also, Philippe Marsol,  Atos BU Transport, Integration Manager says:

    “SafeKit is a simple and powerful product for application high availability. We have integrated SafeKit in our critical projects like the supervision of Paris metro Line 4 (the control room) or Marseille Line 1 and Line 2 (the operations center). Thanks to the simplicity of the product, we gained time for the integration and validation of the solution and we had also quick answers to our questions with a responsive Evidian team.”


  • The software integrator Systel deploys SafeKit high-availability solution in firefighter and emergency medical call centers.

    Healthcare [+]

    The software integrator Systel deploys SafeKit high-availability solution in firefighter and emergency medical call centers.

    Over 30 SafeKit clusters are deployed on Windows with SQL Server.

    Marc Pellas, CEO says:

    "SafeKit perfectly meets the needs of a software vendor. Its main advantage is that it brings in high availability through a software option that is added to our own multi-platform software suite. This way, we are not dependent on a specific and costly hardware clustering solution that is not only difficult to install and maintain, but also differs according to client environments. With SafeKit, our firefighter call centers are run with an integrated software clustering solution, which is the same for all our customers, is user friendly and for which we master the installation up to after-sales support."


  • ERP high availability and load balancing of the French army (DGA) are made with SafeKit.

    Government [+]

    ERP high availability and load balancing of the French army (DGA) are made with SafeKit.

    14 SafeKit clusters are deployed on Windows and Linux.

    Alexandre Barth, Systems administrator says:

    "Our production team implemented the SafeKit solution without any difficulty on 14 Windows and Linux clusters. Our critical activity is thus secure, with high-availability and load balancing functions. The advantages of this product are easy deployment and administration of clusters, on the one hand, and uniformity of the solution in the face of heterogeneous operating systems, on the other hand."

     


SafeKit High Availability Differentiators against Competition

Evidian SafeKit farm cluster with load balancing and failover

No load balancer or dedicated proxy servers or special multicast Ethernet address >

No load balancer or dedicated proxy servers

Like   The solution does not require load balancers or dedicated proxy servers above the farm for imlementing load balancing. SafeKit is installed directly on the application servers in the farm. The load balancing is based on a standard virtual IP address/Ethernet MAC address and is working with physical servers or virtual machines on Windows and Linux without special network configuration

Dislike  This is not the case with network load balancers

Dislike  This is not the case with dedicated proxies on Linux

Dislike  This is not the case with a specific multicast Ethernet address on Windows

All clustering features >

All clustering features

Like  The solution includes all clustering features: virtual IP address, load balancing on client IP address or on sessions, monitoring of server / network / software failures, automatic application restart with a quick revovery time and a replication option with a mirror module

Dislike  This is not the case with other load balancing solutions. They are able to make load balancing but they do not include a full clustering solution with restart scripts and automatic application restart in case of failure. They do not offer a replication option

Like   The cluster configuration is very simple and made with the farm.safe module. There is no domain controller or active directory to configure on Windows. The solution works on Windows and Linux

Remote sites and virtual IP address >

Remote sites

Like   If servers are connected to the same IP network through an extended LAN between remote sites, the virtual IP address of SafeKit is working with load balancing at level 2

Like   If servers are connected to different IP networks between remote sites, the virtual IP address can be configured at the level of a load balancer with the help of the SafeKit health check. Thus you can implement load balancing but also all the clustering features of SafeKit, in particular monitoring and automatic recovery of the critical application on application servers

Uniform high availability solution >

Uniform high availability solution

Like  SafeKit imlements a farm cluster with load balancing and failover. But it implements also a mirror cluster with replication and failover.

Like  Thus a N-tiers architecture can be made highly available and load balanced with the same solution on Windows and Linux (same installation, configuration, administration with the SafeKit console or with the command line interface). This is unique on the market

Dislike  This is not the case with an architecture mixing different technologies for load balancing, replication and failover

Software clustering vs hardware clustering >

A software cluster with SafeKit installed on two servers

Like  A simple software cluster with the SafeKit package just installed on two servers

Hardware clustering with external shared storage

Dislike  Complex hardware clustering with external storage or network load balancers

Shared nothing vs a shared disk cluster >

SafeKit shared-nothing cluster: easy to deploy even in remote sites

Like  SafeKit is a shared-nothing cluster: easy to deploy even in remote sites

Shared disk cluster: complex to deploy

Dislike  A shared disk cluster is complex to deploy

Application High Availability vs Full Virtual Machine High Availability >

SafeKit application high availability supports hardware failure, software failure, human errors

Like  Application HA supports hardware failure and software failure with a quick recovery time (RTO around 1 mn or less).
Smooth upgrade of application and OS possible server by server (version N and N+1 can coexist)

Virtual machines high availability supports only hardware failure with an recovery time depending on the OS reboot

Dislike  Full virtual machines HA supports only hardware failure with a VM reboot and a recovery time depending on the OS reboot.
Smooth upgrade not possible

High availability vs fault tolerance >

SafeKit high availability vs fault-tolerance

Like  No dedicated server with SafeKit. Each server can be the failover server of the other one.
Software failure with restart in another OS environment.
Smooth upgrade of application and OS possible server by server (version N and N+1 can coexist)

Fault tolerance system

Dislike  Secondary server dedicated to the execution of the same application synchronized at the instruction level.
Software exception on both servers at the same time.
Smooth upgrade not possible

Synchronous replication vs asynchronous replication >

SafeKit synchronous replication with no data in case of failure

Like  SafeKit implements real-time synchronous replication with no data loss in case of failure

Asynchronous replication with data loss on failure

Dislike  With asynchronous replication, there is data loss on failure

Byte-level file replication vs block-level disk replication >

SafeKit cluster with byte-level file replication: simply replicates directories even in the system disk

Like  SafeKit implements real-time byte-level file replication and is simply configured with application directories to replicate even in the system disk

Cluster with block-level disk replication: complex and require to put application data in a special disk

Dislike  Block-level disk replication is complex to configure and requires to put application data in a special disk

Heartbeat, failover and quorum to avoid 2 master nodes >

Simple quorum in a SafeKit cluster with a split brain checker configured on a router

Like  To avoid 2 masters, SafeKit proposes a simple split brain checker configured on a router

Complex quorum in other clusters: third machine, special quorum disk, remote hardware reset

Dislike  To avoid 2 masters, other clusters require a complex configuration with a third machine, a special quorum disk, a special interconnect

Virtual IP address
primary/secondary, network load balancing, failover >

No special network configuration in a SafeKit cluster

Like  No dedicated proxy servers and no special network configuration are required in a SafeKit cluster for virtual IP addresses

Special network configuration in other clusters

Dislike  Special network configuration is required in other clusters for virtual IP addresses. Note that SafeKit offers a health check adapted to load balancers

Demonstrations of SafeKit High Availability Software

SafeKit Webinar

This webinar presents in 10 minutes Evidian SafeKit.

In this webinar, you will understand:

  • mirror and farm clusters
  • cost savings against hardware clustering solutions
  • best use cases
  • the integration process for a new application

Microsoft SQL Server Cluster

This video shows a mirror module configuration with synchronous real-time replication and failover.

The file replication and the failover are configured for Microsoft SQL Server but it works in the same manner for other databases.

Free trial here

Apache Cluster

This video shows a farm module configuration with load balancing and failover.

The load balancing and the failover are configured for Apache but it works in the same manner for other web services.

Free trial here

Hyper-V Cluster

This video shows a Hyper-V cluster with full replications of virtual machines.

Virtual machines can run on both Hyper-V servers and they are restarted in case of failure.

Free trial here

Free On-Line Training on SafeKit High Availability Software

SafeKit Modules for Plug&Play High Availability Solutions