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 instructions section.
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 simplicity.
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 SafeKit works in VMware environments without the Microsoft NLB problems of unicast and muticast modes. And note also that SafeKit network load balancing is working not only on Windows (including Windows editions for PCs) but also on Linux.
|OEM Software||Distributed Enterprise||Remote Sites|
|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|
1 - 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.”
2 - The product very easy to deploy for a reseller
“WithNCompany has deployed in South Korea many SafeKit high availability solutions with the Samsung Video Surveillance Platform. SafeKit is appreciated because the product is easy to install and very quickly deployed.”
3 - 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).”
In video surveillance systems, Evidian SafeKit implements high availability with synchronous replication and failover of
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.
Over 30 SafeKit clusters are deployed on AIX and Windows in Natixis.
The Sydel software editor implements high availability of its ERP with SafeKit and deploys the solution in the food industry.
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.
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.
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 Unix platforms. 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.
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.
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.”
Click on the module to understand and try the solution
|Microsoft SQL Server||Windows module||-|
|Oracle||Windows module||Linux module|
|MySQL||Windows module||Linux module|
|PostgreSQL||Windows module||Linux module|
|Firebird||Windows module||Linux module|
|Milestone XProtect (based on Microsoft SQL Server)||Windows module||-|
|Hanwha SSM (based on PostgreSQL)||Windows module||-|
|Generic module||Windows module||Linux module|
|IIS module||Windows module||-|
|Apache module||Windows module||Linux module|
|Generic module||Windows module||Linux module|
High availability architectures comparison
(click on the feature for more information)
|Feature||SafeKit cluster||Other clusters|
|Software clustering vs hardware clustering||
A simple software cluster with the SafeKit package installed on two servers
Complex hardware clustering with external storage or network load balancers
|Shared nothing vs a shared disk cluster||
SafeKit is a shared-nothing cluster: easy to deploy even in remote sites
A shared disk cluster is complex to deploy
|Application High Availability vs Full Virtual Machine High Availability||
SafeKit application HA supports hardware failure, software failure, human errors with quick recovery time
Full virtual machines HA supports only hardware failure with a VM reboot and an unknown recovery time if the OS reboot does not work
|Synchronous replication vs asynchronous replication||
SafeKit implements real-time synchronous replication with no data loss in case of failure
With asynchronous replication, there is data loss on failure
|Byte-level file replication vs block-level disk replication||
SafeKit implements byte-level file replication and is simply configured with directories to replicate even in the system disk
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||
To avoid 2 masters, SafeKit proposes a simple split brain checker configured on a router
To avoid 2 masters, other clusters require a complex configuration with a third machine, a special quorum disk, a special interconnect
|Network load balancing||
No special network configuration is required in a SafeKit cluster for network load balancing
Special network configuration is required in other clusters for network load balancing
RTO is the time during which the application is unavailable in case of failure. RTO of the SafeKit farm solution is in the order of a few seconds on hardware failure.
For a hardware failure, RTO = failure detection timeout through monitoring channels (default a few seconds): after the timeout the load balancing filters are reconfigured.
For a software failure or an administrator restart, RTO = time to (cleanly) stop Linux services + time to restart them.
On both Linux servers
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.
Launch the web console in a browser by connecting to http://localhost:9010 (next image)
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)
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 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.
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 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).
Check with Linux command lines that the Linux services are started 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 that the Linux services are stopped on the STOP node with Linux command lines.
To understand what happens in the cluster, check the SafeKit logs of node 1 and node 2.
To see the module log of node 1 (next image):
To see the application log of node 1 (next image):
To see the logs of node 2 (previous image), click on W12R2server75/UP (it will become blue) on the left side and repeat the same operations.
In Advanced Configuration tab, 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.
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.
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 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>
#!/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
#!/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"