Cloud: The Simplest High Availability Cluster with Synchronous Real-Time Replication and Failover between Two Redundant Windows or Linux Servers
Cloud: The Simplest High Availability Cluster with Synchronous Real-Time Replication and Failover
Evidian SafeKit
How the Evidian SafeKit software simply implements high availability with synchronous real-time replication and failover in Cloud between two redundant Windows or Linux servers without shared storage?
Evidian SafeKit provides a high availability cluster with real-time replication and failover in Cloud.
This article explains how to implement quickly such a cluster in Cloud.
A free trial is offered below with a quick start template for an easy deployment in the Cloud.
Note that SafeKit is a generic product.
You can implement with the same product real-time replication and failover
of new 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,
the servers are running in different availability zones
the critical application is running on the PRIM server
users are connected to a primary/secondary virtual IP address which is configured in the load balancer
SafeKit provides a generic health check for the load balancer.
On the PRIM server, the health check returns OK to the load balancer and NOK on the SECOND server.
in each server, SafeKit monitors the critical application with process checkers and custom checkers
SafeKit restarts automatically the critical application when there is a software failure or a hardware failure thanks to restart scripts
SafeKit makes synchronous real-time replication of files containing critical data
a connector for the SafeKit web console is installed in each server.
Thus, the high availability cluster can be managed in a very simple way to avoid human errors
On the previous figure, the server 1/PRIM runs the critical application. Users are connected to the virtual IP address of the mirror cluster. SafeKit replicates files opened by the critical application in real time. Only changes in the files are replicated across the network, thus limiting traffic (byte-level file replication). Names of file directories containing critical data are simply configured in SafeKit. There are no pre-requisites on disk organization for the two servers. Directories to replicate may be located in the system disk. SafeKit implements synchronous replication with no data loss on failure contrary to asynchronous replication.
The load balancer must be configured to periodically send health packets to virtual machines.
For that, SafeKit provides a health check which runs inside the virtual machines and which
returns OK when the mirror module state is PRIM (green) or ALONE (green)
returns NOT FOUND in all other states
You must configure the Cloud load balancer with:
HTTP protocol
port 9010, the SafeKit web server port
URL /var/modules/mirror/ready.txt (if mirror is the module name that you will deploy later)
For more information, see the configuration of the Cloud load balancer.
Configuration of the Cloud network security
The network security must be configured to enable communications for the following protocols and ports:
UDP - 4800 for the safeadmin service (between SafeKit nodes)
UDP - 8888 for the module heartbeat (between SafeKit nodes)
TCP – 5600 for the module real time file replication (between SafeKit nodes)
TCP – 9010 for the load-balancer health check and for the SafeKit web console running in the http mode
TCP – 9001 to configure the https mode for the console
TCP – 9453 for the SafeKit web console running in https mode
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 mirror.safe is delivered inside the package.
Configuration of SafeKit
The configuration is presented with the web console connected to 2 Windows servers but it is the same thing with 2 Linux servers.
Important: all the configuration is made from a single browser.
It is recommended to configure the web console in the https mode by connecting to https://<IP address of 1 VM>:9453 (next image). In this case, you must configure before the https mode by using the wizard described in the User's Guide: see "11. Securing the SafeKit web console".
Or you can use the web console in the http mode by connecting to http://<IP address of 1 VM>:9010 (next image).
Note that you can also make a configuration with DNS names, especially if the IP addresses are not static.
Enter IP address of the first node and click on Confirm (next image)
Click on New node and enter IP address of the second node (next image)
Click on the red floppy disk to save the configuration (previous image)
In the Configuration tab, click on mirror.safe then enter mirror as the module name and Confirm: next images with mirror instead of xxx
Click on Validate (next image)
Change the path of replicated directories only if necessary (next image).
Do not configure a virtual IP address (next image) because this configuration is already made in the Cloud load balancer. This section is useful for on-premise configuration only.
If a process is defined in the Process Checker section (next image), it will be monitored on the primary server with the action restart in case of failure.
The services will be stopped an restarted locally on the primary 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 there is a failover on the secondary server.
As a consequence, the health check answers OK on the new primary server to the Cloud load balancer and the virtual IP address traffic is switched to the new primary server.
start_prim and stop_prim (next image) contain the start and the stop of services.
Note:
on Windows, put services with Boot Startup Type = Manual on both servers (SafeKit controls start of services in start_prim).
Click on Validate (previous image)
Click on Configure (previous image)
Check the success green message on both servers and click on Next (previous image).
On Linux, you may have an error at this step if replicated directories are mount points. See this article to solve the problem.
Select the node with the most up-to-date replicated directories and click on start it to make the first resynchronization in the right direction (previous image). Before this operation, we suggest you to make a copy of replicated directories before starting the cluster to avoid any errors.
Start the second node (previous image) which becomes SECOND green (next image) after resynchronisation of all replicated directories (binary copy from node 1 to node 2).
The cluster is operational with services running on the PRIM node and nothing running on the SECOND node (previous image). Only modifications inside files are replicated in real-time in this state.
Be careful, components which are clients of the 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 Windows Microsoft Management Console (MMC) or with Linux command lines that the services are started on the primary server and stopped on the secondary server.
Stop the PRIM node by scrolling down the menu of the primary node and by clicking on Stop. Check that there is a failover on the SECOND node. And check the failover of services with Windows Microsoft Management Console (MMC) or with Linux command lines.
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 servers once the high availability solution is correctly running.
Note that on Windows, with Windows services manager, we assume that services are with Boot Startup Type = Manual on both nodes. SafeKit controls start of services when starting the module in start_prim.
Note that for synchronizing SafeKit at boot and at shutdown on Windows, we assume that a command line has been run on both nodes during installation as administrator: .\addStartupShutdown.cmd in C:\safekit\private\bin
(otherwise dot it now).
For reading the SafeKit logs, go to the Troubleshooting tab
For editing userconfig.xml, start_prim and stop_prim, go to the Advanced Configuration tab
Troubleshooting of a SafeKit / high availability cluster with real-time synchronous replication and failover between two redundant servers
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 the primary server (next image):
click on the Control tab
click on node 1/PRIM (it becomes blue) on the left side to select the server
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 the secondary server.
Application log
Read the application log to see the output messages of the stat_prim and stop_prim restart scripts.
To see the application log of the primary server (next image):
click on the Control tab
click on node 1/PRIM (it becomes blue) on the left side to select the server
click on Application Log to see messages when starting and stopping 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 the secondary server.
Advanced configuration of a SafeKit / high availability cluster with real-time synchronous replication and failover between two redundant servers
In Advanced Configuration tab (next image), you can edit internal files of the module: bin/start_prim and bin/stop_prim 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 icon/xxx on the left side (next image): the interface will allow you to redeploy the modified files on both servers.
For an example of userconfig.xml, start_prim and stop_prim, go to the Internals tab
Support of a SafeKit / high availability cluster with real-time synchronous replication and failover between two redundant servers
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).
<!DOCTYPE safe>
<safe>
<service mode="mirror" defaultprim="alone" maxloop="3" loop_interval="24" failover="on">
<!-- Server Configuration -->
<!-- Names or IP addresses on the default network are set during initialization in the console -->
<heart pulse="700" timeout="30000">
<heartbeat name="default" ident="flow"/>
</heart>
<!-- Software Error Detection Configuration -->
<!-- Replace
* PROCESS_NAME by the name of the process to monitor
-->
<errd polltimer="10">
<proc name="PROCESS_NAME" atleast="1" action="restart" class="prim" />
</errd>
<!-- File Replication Configuration -->
<rfs async="second" acl="off" nbrei="3">
<replicated dir="c:\test1replicated" mode="read_only"/>
<replicated dir="c:\test2replicated" mode="read_only"/>
</rfs>
<!-- User scripts activation -->
<user nicestoptimeout="300" forcestoptimeout="300" logging="userlog"/>
</service>
</safe>
start_prim.cmd on Windows
@echo off
rem Script called on the primary server for starting application services
rem For logging into SafeKit log use:
rem “%SAFE%\safekit” printi | printe "message"
rem stdout goes into Application log
echo "Running start_prim %*"
set res=0
rem Fill with your services start call
set res=%errorlevel%
if %res% == 0 goto end
:stop
“%SAFE%\safekit” printe "start_prim failed"
rem uncomment to stop SafeKit when critical
rem “%SAFE%\safekit” stop -i "start_prim"
:end
stop_prim.cmd on Windows
@echo off
rem Script called on the primary server for stopping application services
rem For logging into SafeKit log use:
rem “%SAFE%\safekit” printi | printe "message"
rem ----------------------------------------------------------
rem
rem 2 stop modes:
rem
rem - graceful stop
rem call standard application stop with net stop
rem
rem - force stop (%1=force)
rem kill application's processes
rem
rem ----------------------------------------------------------
rem stdout goes into Application log
echo "Running stop_prim %*"
set res=0
rem default: no action on forcestop
if "%1" == "force" goto end
rem Fill with your services stop call
rem If necessary, uncomment to wait for the stop of the services
rem “%SAFEBIN%\sleep” 10
if %res% == 0 goto end
“%SAFE%\safekit” printe "stop_prim failed"
:end
<!DOCTYPE safe>
<safe>
<service mode="mirror" defaultprim="alone" maxloop="3" loop_interval="24" failover="on">
<!-- Server Configuration -->
<!-- Names or IP addresses on the default network are set during initialization in the console -->
<heart pulse="700" timeout="30000">
<heartbeat name=”default” ident=”flow”/>
</heart>
<!-- Software Error Detection Configuration -->
<!-- Replace
* PROCESS_NAME by the name of the process to monitor
-->
<errd polltimer="10">
<proc name="PROCESS_NAME" atleast="1" action="restart" class="prim" />
</errd>
<!-- File Replication Configuration -->
<rfs mountover="off" async="second" acl="off" nbrei="3" >
<replicated dir="/test1replicated" mode="read_only"/>
<replicated dir="/test2replicated" mode="read_only"/>
</rfs>
<!-- User scripts activation -->
<user nicestoptimeout="300" forcestoptimeout="300" logging="userlog"/>
</service>
</safe>
start_prim on Linux
#!/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_prim $*"
res=0
# Fill with your application start call
if [ $res -ne 0 ] ; then
$SAFE/safekit printe "start_prim failed"
# uncomment to stop SafeKit when critical
# $SAFE/safekit stop -i "start_prim"
fi
stop_prim on Linux
#!/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_prim $*"
res=0
# default: no action on forcestop
[ "$1" = "force" ] && exit 0
# Fill with your application stop call
[ $res -ne 0 ] && $SAFE/safekit printe "stop_prim failed"
SafeKit Modules for Plug&Play High Availability Solutions
Network load balancing and failover: click on the blue buttons
Farm modules
Windows
Linux
New application
IIS
-
Apache
Amazon AWS farm
Microsoft Azure farm
Google GCP farm
Cloud generic farm
Real-time file replication and failover: click on the blue buttons
Mirror modules
Windows
Linux
New application
Microsoft SQL Server
-
Oracle
MariaDB
MySQL
PostgreSQL
Firebird
Hyper-V
-
KVM
-
Docker
-
Elasticsearch
-
Milestone XProtect
-
Genetec SQL Server
-
Hanwha Wisenet SSM
-
Nedap AEOS
-
Amazon AWS mirror
Microsoft Azure mirror
Google GCP mirror
Cloud generic mirror
Customers of SafeKit High Availability Software in all Business Activities
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."
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 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.”
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."
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.”
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."
"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
Key differentiators of a mirror cluster with replication and failover
Evidian SafeKit mirror cluster with real-time file replication and failover
A SafeKit cluster runs on Windows and Linux without the need for expensive shared or replicated disk bays
SafeKit includes
all clustering features:
synchronous real-time file replication, monitoring of server/network/software failures, automatic
application
restart, virtual IP address switched in case of failure to reroute clients
This is not the case with replication-only solutions like replication at the database level which implements only replication
The cluster configuration is very simple and made
by means of application modules.
There is no domain controller or active directory to configure as with Microsoft cluster
SafeKit implements quick
application
restart in case of failure: around 1 mn or less (see RTO/RPO here)
Quick
application
restart is not ensured with full virtual machines replication. In case of hypervisor failure, a full VM must be rebooted on a new hypervisor with a recovery time depending on the OS reboot as with VMware HA or Hyper-V cluster
After a failure when a server reboots, the replication failback procedure
is fully automatic and the failed server reintegrates the cluster without stopping
the application
on the only remaining server
This is not the case with most replication solutions particularly with replication at the database level. Manual operations are required for resynchronizing a failed server.
The application
may even be stopped on the only remaining server during the resynchonization of the failed server
All SafeKit clustering features are working for 2 servers in remote sites. Performances of replication depends on the interconnect latency for real-time synchronous replication and on the bandwidth for resynchronizing data on a failed server
If both servers are connected to the same IP network through an extended LAN between two remote sites, the virtual IP address of SafeKit is working with rerouting at level 2
If both servers are connected to two different IP networks between two remote sites, the virtual IP address can be configured at the level of a load balancer.
SafeKit offers a health check: the load balancer is configured with a URL managed by SafeKit which returns OK on the primary server and NOT FOUND else. This solution is implemented for SafeKit in the Cloud but it can be also implemented with a load balancer on premise
The secondary server is not dedicated to the restart of the primary server. The cluster can be active-active by running 2 different mirror modules
This is not the case with a fault-tolerant system where the secondary is dedicated to the execution of the same application synchronized at the instruction level
SafeKit implements a mirror cluster with replication and failover. But it imlements also
a farm cluster with load balancing and failover.
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
This is not the case with an architecture mixing different technologies for load balancing, replication and failover
Key differentiators of a farm cluster with load balancing and failover
Evidian SafeKit farm cluster with load balancing and failover
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
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
The cluster configuration is very simple and made
by means of application modules.
There is no domain controller or active directory to configure on Windows. The solution works on Windows and Linux
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
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.
SafeKit offers a health check: the load balancer is configured with a URL managed by SafeKit which returns OK on the UP servers and NOT FOUND else.
This solution is implemented for SafeKit in the Cloud
but it can be also implemented with a load balancer on premise.
Thus you can implement load balancing but also all the clustering features of SafeKit including an easy administration of the cluster through the SafeKit web console
SafeKit imlements a farm cluster with load balancing and failover.
But it implements also a mirror cluster with replication and failover.
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
This is not the case with an architecture mixing different technologies for load balancing, replication and failover
Key differentiators of the SafeKit high availability technology
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)
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
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)
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
No dedicated proxy servers and no special network configuration are required in a SafeKit cluster for virtual IP addresses
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.
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OEM Software
This is not the case with replication-only solutions like replication at the database level which implements only replication
