High Availability Architectures Overview
Principle of high availability modules
A high availability module is a customization of SafeKit for an application. There are two types of modules: the mirror module with real-time data replication and failover and the farm module with load balancing and failover.
In practice, an application module is a “.Safe” file (zip type) including:
1 - the configuration file userconfig.xml which contains:
- names or physical IP addresses of the servers,
- name or virtual IP address of the cluster,
- file directories to replicate in real time (for a mirror module),
- network load balancing criteria (for a farm module),
- configuration of software and hardware failures detectors
2 - the scripts to start and stop the application.
Examples of HA modules are given in this article.
Plug and play deployment of high availability modules
Once an application module is configured and tested with an application, deployment requires no specific IT skills:
- install application on 2 standard servers (physical or virtual),
- install the SafeKit software on both servers,
- install the application module on both servers.
High availability architectures: the different software clusters
SafeKit offers two basic clusters:
- the mirror cluster built by deploying a mirror application module on 2 servers,
- the farm cluster built by deploying a farm application module on 2 servers or more.
Several application modules can be deployed on the same cluster. Thus, advanced clustering architectures can be implemented:
- a farm+mirror cluster with the deployment of one farm module and one mirror module on the same cluster,
- an active/active cluster with the deployment of several mirror modules on 2 servers,
- a Hyper-V cluster with replication and failover of full VMs between 2 active physical servers,
- a N-1 cluster with the deployment of N mirror module on N+1 servers.
FAQ on Evidian SafeKit
Best use cases [+]
Customers [+]
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Video Surveillance (CCTV) [+]
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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 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.”
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Application high availability modules [+]
SafeKit Webinar [+]
Pricing - Free trial [+]
Comparison with other solutions [+]
Demonstration of a mirror cluster [+]
What are the advantages of the mirror cluster [+]
- Low Complexity
- Plug&Play deployment with no specific skills
- Suitable for large deployments in many sites (very simple to deploy)
- 2 nodes (3 nodes replication possibility)
- No shared storage requirement
- No Domain Controller requirement
- Well documented API and support
- Synchronous data replication (no data loss in case of failure)
- Replicated directories can be in the system disk
- Supports multiple heartbeats and vitual IP addresses
- Offers configurable software, hardware and network checkers
- For the quorum, does not require a special disk or a third machine or a dedicated link between both servers
- Automatic failover of services with a recovery time in the order of one minute
- Automatic failback when a server comes back after a failure (no manual operation)
- A very simple console to deploy the solution and to maintain it afterwards for end-customer
- Supports human errors (40% of causes of unavailability) thanks to its simplicity
- Supports software failures (40% of causes of unavailability): regression on software update (version N and N+1 can coexist), Operating System frozen, software bug
- Supports hardware and environment failures (20% of causes of unavailability), including the complete failure of a computer room with 2 nodes in two remote sites
What is the recovery time (RTO) in a mirror cluster [+]
RTO is the time during which the application is unavailable in case of failure. RTO of the SafeKit mirror solution is in the order of 1 mn.
For a hardware failure, RTO = heartbeat timeout (default 30 s, can be changed in userconfig.xml) + time to restart services.
For a software failure or an administrator restart, RTO = time to (cleanly) stop services + time to restart them.
Be careful, with solutions that reboot a full virtual machine in case of failure, the RTO is unpredictable as manual operations may be required after a hardware crash to reboot the virtual machine.
What is the data loss (RPO) in a mirror cluster [+]
RPO reflects the data loss in case of failure. RPO of the SafeKit mirror solution is 0 as the replication is synchronous and real-time.
Be careful, with asynchronous replication, RPO is not 0 and there is data loss in case of failure when the application restarts on the secondary server.
Demonstration of a farm cluster [+]
What are the advantages of the farm cluster [+]
- Low Complexity
- Plug&Play deployment with no specific skills
- Suitable for large deployments in many sites (very simple to deploy)
- 2 nodes or more
- No network load balancers requirement
- No proxy server requirement (above the farm cluster)
- No Domain Controller requirement
- No restriction in VMware due to multicast or unicast address
- Same solution on Windows and Linux
- Well documented API and support
- Supports multiple monitoring channels on multiple networks for server failure detection
- Supports multiple vitual IP addresses
- Offers configurable software, hardware and network checkers
- Offers the mirror cluster with synchronous real-time replication and failover
- Automatic failover with a recovery time in the order of a few seconds
- Automatic failback when a server comes back after a failure (no manual operation)
- A very simple console to deploy the solution and to maintain it afterwards for end-customer
- Supports human errors (40% of causes of unavailability) thanks to its simplicity
- Supports software failures (40% of causes of unavailability): regression on software update (version N and N+1 can coexist), Operating System frozen, software bug
- Supports hardware and environment failures (20% of causes of unavailability), including the complete failure of a computer room with 2 nodes in two remote sites
What is the recovery time (RTO) in a farm cluster [+]
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 services + time to restart them.
