How the Evidian SafeKit software simply implements a load balancing cluster with failover in Cloud?
The solution in Cloud
Evidian SafeKit brings load balancing and failover in Cloud between two Windows or Linux redundant servers or more.
This article explains how to implement quickly a Cloud cluster without specific skills.
A generic product
Note that SafeKit is a generic product on Windows and Linux.
You can implement with the same product real-time replication and failover of any file directory and service, database, complete Hyper-V or KVM virtual machines, Docker, Kubernetes , Cloud applications.
Architecture
How it works in Cloud?
The servers are running in different availability zones.
The critical application is running in all servers of the farm.
Users are connected to a virtual IP address which is configured in the Cloud load balancer.
SafeKit provides a generic health check for the load balancer.
When the farm module is stopped in a server, the health check returns NOK to the load balancer which stops the load balancing of requests to the server.
The same behavior happens when there is a hardware failure.
In each server, SafeKit monitors the critical application with process checkers and custom checkers.
SafeKit restarts automatically the critical application in a server when there is a software failure thanks to restart scripts.
A connector for the SafeKit web console is installed in each server.
Thus, the load balancing cluster can be managed in a very simple way to avoid human errors.
SafeKit: an ideal solution for a partner application
This platform agnostic solution is ideal for a partner with a critical application and who wants to provide a high availability option easy to deploy to many customers.
This clustering solution is also recognized as the simplest to implement by our partners.
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 farm module state is UP (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/farm/ready.txt (if farm 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)
TCP – 9010 for the load-balancer health check and for the SafeKit web console running the http mode
TCP – 9001 to configure the https mode for the console
TCP – 9453 for the SafeKit web console running in the 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 farm.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 must be done 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 "11.1 HTTPS Quick Configuration with the Configuration Wizard".
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 farm.safe then enter farm as the module name and Confirm (next images with farm instead of xxx)
Click on Validate (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 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. As a consequence, the health check answers NOT FOUND to the Cloud load balancer and the load balancing is reconfigured to load balance the traffic on the remaining servers of the farm.
start_both and stop_both (next image) contain the start and the stop of services.
Click on Validate (previous image)
Click on Configure (previous image)
Check the success green message on both servers and click on Next (previous image)
Start the cluster on both nodes (previous image).
Check that the status becomes UP (green) - UP (green) (next image).
The cluster is operational with services running on both UP nodes (previous image).
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 both UP nodes. Put services with Boot Startup Type = Manual (SafeKit controls start of 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 that the services are stopped on the STOP node 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 nodes once the load balancing and failover solution is correctly running.
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_both and stop_both, go to the Advanced Configuration tab
Troubleshooting
Troubleshooting with the SafeKit module and application logs
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.
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 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.
Advanced configuration of SafeKit for implementing the 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.
For an example of userconfig.xml, start_both and stop_both, open the Internals section below
Support
Support of SafeKit
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).
<!DOCTYPE safe>
<safe>
<service mode="farm" maxloop="3" loop_interval="24">
<!-- Farm topology configuration -->
<!-- Names or IP addresses on the default network are set during initialization in the console -->
<farm>
<lan name="default" />
</farm>
<!-- 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="both" />
</errd>
<!-- User scripts activation -->
<user nicestoptimeout="300" forcestoptimeout="300" logging="userlog" />
</service>
</safe>
start_both.cmd on Windows
@echo off
rem Script called on all servers for starting applications
rem For logging into SafeKit log use:
rem "%SAFE%\safekit" printi | printe "message"
rem stdout goes into Application log
echo "Running start_both %*"
set res=0
rem Fill with your services start call
set res=%errorlevel%
if %res% == 0 goto end
:stop
set res=%errorlevel%
"%SAFE%\safekit" printe "start_both failed"
rem uncomment to stop SafeKit when critical
rem "%SAFE%\safekit" stop -i "start_both"
:end
stop_both.cmd on Windows
@echo off
rem Script called on all servers for stopping application
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_both %*"
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 real stop of services
rem "%SAFEBIN%\sleep" 10
if %res% == 0 goto end
"%SAFE%\safekit" printe "stop_both failed"
:end
<!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>
<!-- 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="both" />
</errd>
<!-- User scripts activation -->
<user nicestoptimeout="300" forcestoptimeout="300" logging="userlog" />
</service>
</safe>
start_both 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_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 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_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"
SafeKit high availability software on Windows and Linux saves on 1/ costly external shared or replicated storage, 2/ load balancing boxes, 3/ enterprise editions of OS and databases
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
The cluster configuration is very simple and made
with the .safe module.
by means of application modules.
New services and new replicated directories can be added to an existing application module
to complete a high availability solution
All the configuration of clusters is made using a simple centralized web administration console
There is no domain controller or active directory to configure as with Microsoft 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. Replication requires an extended LAN type network (latency = performance of synchronous replication, bandwidth = performance of resynchronization after failure).
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 with the "healh check" of SafeKit.
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
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
Key differentiators of a farm cluster with load balancing and failover
Evidian SafeKit farm cluster with load balancing and failover
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
This is not the case with network load balancers
This is not the case with dedicated proxies on Linux
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 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
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).
Application HA requires to define restart scripts per application and folders to replicate (SafeKit application modules).
Full virtual machines HA supports only hardware failure with a VM reboot and a recovery time depending on the OS reboot.
No restart scripts to define with full virtual machines HA (SafeKit hyperv.safe or kvm.safe modules). Hypervisors are active/active with just multiple virtual machines.
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
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SafeKit high availability software on Windows and Linux saves on 1/ costly external shared or replicated storage, 2/ load balancing boxes, 3/ enterprise editions of OS and databases
This is not the case with asynchronous replication
