High Availability Architectures Overview

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.

High availability architecture

In practice, an application module is a “.Safe” file (zip type) including:

1 - the configuration file userconfig.xml which contains:

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:

  1. install application on 2 standard servers (physical or virtual),
  2. install the SafeKit software on both servers,
  3. install the application module on both servers.

High availability architectures: the different software clusters

SafeKit offers two basic clusters:

Several application modules can be deployed on the same cluster. Thus, advanced clustering architectures can be implemented:

Key differentiators of file replication and failover with the Evidian SafeKit mirror cluster

Evidian SafeKit mirror cluster with real-time file replication and failover

All clustering features All clustering features

Like  The solution includes all clustering features: server failure monitoring, network failure monitoring, software failure monitoring, automatic application restart with a quick recovery time, a virtual IP address switched in case of failure to automatically reroute clients

Dislike  This is not the case with replication-only solutions like replication at the database level

Dislike  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 an unknown recovery time

Like   The cluster configuration is very simple and made by means of a high availability application module. There is no domain controller or active directory to configure on Windows. The solution works on Windows and Linux

Synchronous replication Synchronous replication

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

Dislike  This is not the case with asynchronous replication

Fully automated failback procedure Automatic failback

Like  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

Dislike  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

Replication of any type of data

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

Dislike  This not the case for replication at the database level

File replication vs disk replication File replication vs disk replication

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

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

File replication vs shared disk File replication vs shared disk

Like  The servers can be put in two remote sites

Dislike  This is not the case with shared disk solutions

Remote sites Remote sites

Like  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

Like  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

Like  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

Quorum Quorum

Like  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

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

Uniform high availability solution Uniform high availability solution

Like  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

Dislike  This is not the case with an architecture mixing different technologies for load balancing, replication and failover

Key differentiators of load balancing and failover with the Evidian SafeKit farm cluster

Evidian SafeKit farm cluster with load balancing and failover

No load balancer or dedicated proxy servers or special multicast Ethernet address No load balancer or dedicated proxy servers

Like   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

Dislike  This is not the case with network load balancers

Dislike  This is not the case with dedicated proxies on Linux

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

All clustering features All clustering features

Like  The solution includes all clustering features: virtual IP address, load balancing on client IP address or on sessions, server failure monitoring, network failure monitoring, software failure monitoring, automatic application restart with a quick revovery time and a replication option with a mirror module

Dislike  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

Like   The cluster configuration is very simple and made by means of a high availability application module. There is no domain controller or active directory to configure on Windows. The solution works on Windows and Linux

Remote sites Remote sites

Like   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

Like   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

Uniform high availability solution Uniform high availability solution

Like  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 me 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

Dislike  This is not the case with an architecture mixing different technologies for load balancing, replication and failover

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