Clustering software vs hardware clustering - simplicity vs complexity

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

  The real-time replication is synchronous with no data loss on failure

  This is not the case with asynchronous replication

  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

  The replication is working for databases but also for any files which shall be replicated

  This not the case for replication at the database level

  The replication is based on file directories that can be located anywhere (even in the system disk)

  This is not the case with disk replication where special application configuration must be made to put the application data in a special disk

  The servers can be put in two remote sites

  This is not the case with shared disk solutions

  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

  With remote sites, the solution works with only 2 servers and for the quorum (network isolation), a simple split brain checker to a router is offered to support a single execution

  This is not the case for most clustering solutions where a 3^rd server is required for the quorum

  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

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

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

  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