Active active cluster with real-time replication
Evidian SafeKit
Active- active cluster with real-time replication
Applications are running on two servers in mutual failover. Each server is backup of the other server. And each application works on its own replicated file directories.
If one server fails in an active active cluster, all applications will be active on the same server. After restart of the failed server, applications will return to run on their default primary server.
How it works?
The SafeKit active active cluster is simply configured by deploying two mirror modules with real-time replication. Each mirror module contains its own configuration of virtual IP address, real-time replicated directories and restart scripts.
Note that:
- the 2 applications Appli1 and Appli2 must be installed on each server for application failover,
- this architecture is not reduced to 2 applications: N application modules can be deployed on 2 servers with a maximum of 25 modules,
- each mirror module will have its own virtual IP address, its own replicated file directories and its own recovery scripts.
Example of an active active cluster
The Hyper-V or KVM solution with replication, automatic failover and load balancing of VMs is an example of an active-active cluster with N mirror modules replicating N virtual machines between two physical servers.
In this configuration, a mirror module replicates a full virtual machine and restarts the virtual machine in case of failure.
There is no virtual IP address in such a module because restarting a VM on a server makes automatically the failover of the VM physical IP address.
And a critical application is installed inside a VM in this architecture.
Partners, the success with SafeKit
This platform agnostic solution is ideal for a partner reselling a critical application and who wants to provide a redundancy and high availability option easy to deploy to many customers.
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Step 1. Real-time replication
Server 1 (PRIM) runs the Windows or Linux application. Clients are connected to a virtual IP address. SafeKit replicates in real time modifications made inside files through the network.
The replication is synchronous with no data loss on failure contrary to asynchronous replication.
You just have to configure the names of directories to replicate in SafeKit. There are no pre-requisites on disk organization. Directories may be located in the system disk.
Step 2. Automatic failover
When Server 1 fails, Server 2 takes over. SafeKit switches the virtual IP address and restarts the Windows or Linux application automatically on Server 2.
The application finds the files replicated by SafeKit uptodate on Server 2. The application continues to run on Server 2 by locally modifying its files that are no longer replicated to Server 1.
The failover time is equal to the fault-detection time (30 seconds by default) plus the application start-up time.
Step 3. Automatic failback
Failback involves restarting Server 1 after fixing the problem that caused it to fail.
SafeKit automatically resynchronizes the files, updating only the files modified on Server 2 while Server 1 was halted.
Failback takes place without disturbing the Windows or Linux application, which can continue running on Server 2.
Step 4. Back to normal
After reintegration, the files are once again in mirror mode, as in step 1. The system is back in high-availability mode, with the Windows or Linux application running on Server 2 and SafeKit replicating file updates to Server 1.
If the administrator wishes the application to run on Server 1, he/she can execute a "swap" command either manually at an appropriate time, or automatically through configuration.
More information on power outage and network isolation in a cluster.
Redundancy at the application level
In this type of solution, only application data are replicated. And only the application is restared in case of failure.
With this solution, restart scripts must be written to restart the application.
We deliver application modules to implement redundancy at the application level (like the mirror module provided in the free trial below). They are preconfigured for well known applications and databases. You can customize them with your own services, data to replicate, application checkers. And you can combine application modules to build advanced multi-level architectures.
This solution is platform agnostic and works with applications inside physical machines, virtual machines, in the Cloud. Any hypervisor is supported (VMware, Hyper-V...).
Redundancy at the virtual machine level
In this type of solution, the full Virtual Machine (VM) is replicated (Application + OS). And the full VM is restarted in case of failure.
The advantage is that there is no restart scripts to write per application and no virtual IP address to define. If you do not know how the application works, this is the best solution.
This solution works with Windows/Hyper-V and Linux/KVM but not with VMware. This is an active/active solution with several virtual machines replicated and restarted between two nodes.
- Solution for a new application (no restart script to write): Windows/Hyper-V, Linux/KVM
More comparison between VM HA vs Application HA
Why a replication of a few Tera-bytes?
Resynchronization time after a failure (step 3)
- 1 Gb/s network ≈ 3 Hours for 1 Tera-bytes.
- 10 Gb/s network ≈ 1 Hour for 1 Tera-bytes or less depending on disk write performances.
Alternative
- For a large volume of data, use external shared storage.
- More expensive, more complex.
Why a replication < 1,000,000 files?
- Resynchronization time performance after a failure (step 3).
- Time to check each file between both nodes.
Alternative
- Put the many files to replicate in a virtual hard disk / virtual machine.
- Only the files representing the virtual hard disk / virtual machine will be replicated and resynchronized in this case.
Why a failover ≤ 32 replicated VMs?
- Each VM runs in an independent mirror module.
- Maximum of 32 mirror modules running on the same cluster.
Alternative
- Use an external shared storage and another VM clustering solution.
- More expensive, more complex.
Why a LAN/VLAN network between remote sites?
- Automatic failover of the virtual IP address with 2 nodes in the same subnet.
- Good bandwidth for resynchronization (step 3) and good latency for synchronous replication (typically a round-trip of less than 2ms).
Alternative
- Use a load balancer for the virtual IP address if the 2 nodes are in 2 subnets (supported by SafeKit, especially in the cloud).
- Use backup solutions with asynchronous replication for high latency network.
Network load balancing and failover |
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Windows farm | Linux farm |
Generic Windows farm > | Generic Linux farm > |
Microsoft IIS > | - |
NGINX > | |
Apache > | |
Amazon AWS farm > | |
Microsoft Azure farm > | |
Google GCP farm > | |
Other cloud > |
Advanced clustering architectures
Several modules can be deployed on the same cluster. Thus, advanced clustering architectures can be implemented:
- the farm+mirror cluster built by deploying a farm module and a mirror module on the same cluster,
- the active/active cluster with replication built by deploying several mirror modules on 2 servers,
- the Hyper-V cluster or KVM cluster with real-time replication and failover of full virtual machines between 2 active hypervisors,
- the N-1 cluster built by deploying N mirror modules on N+1 servers.
Evidian SafeKit mirror cluster with real-time file replication and failover |
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3 products in 1 More info > |
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Very simple configuration More info > |
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Synchronous replication More info > |
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Fully automated failback More info > |
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Replication of any type of data More info > |
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File replication vs disk replication More info > |
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File replication vs shared disk More info > |
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Remote sites and virtual IP address More info > |
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Quorum and split brain More info > |
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Active/active cluster More info > |
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Uniform high availability solution More info > |
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RTO / RPO More info > |
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Evidian SafeKit farm cluster with load balancing and failover |
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No load balancer or dedicated proxy servers or special multicast Ethernet address |
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All clustering features |
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Remote sites and virtual IP address |
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Uniform high availability solution |
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Software clustering vs hardware clustering
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Shared nothing vs a shared disk cluster |
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Application High Availability vs Full Virtual Machine High Availability
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High availability vs fault tolerance
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Synchronous replication vs asynchronous replication
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Byte-level file replication vs block-level disk replication
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Heartbeat, failover and quorum to avoid 2 master nodes
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Virtual IP address primary/secondary, network load balancing, failover
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Evidian SafeKit 8.2
All new features compared to SafeKit 7.5 described in the release notes
Packages
- Windows (with Microsoft Visual C++ Redistributable)
- Windows (without Microsoft Visual C++ Redistributable)
- Linux
- Supported OS and last fixes
One-month license key
Technical documentation
Training
Product information
Introduction
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- Demonstration
- Examples of redundancy and high availability solution
- Evidian SafeKit sold in many different countries with Milestone
- 2 solutions: virtual machine or application cluster
- Distinctive advantages
- More information on the web site
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- Cluster of virtual machines
- Mirror cluster
- Farm cluster
Installation, Console, CLI
- Install and setup / pptx
- Package installation
- Nodes setup
- Upgrade
- Web console / pptx
- Configuration of the cluster
- Configuration of a new module
- Advanced usage
- Securing the web console
- Command line / pptx
- Configure the SafeKit cluster
- Configure a SafeKit module
- Control and monitor
Advanced configuration
- Mirror module / pptx
- start_prim / stop_prim scripts
- userconfig.xml
- Heartbeat (<hearbeat>)
- Virtual IP address (<vip>)
- Real-time file replication (<rfs>)
- How real-time file replication works?
- Mirror's states in action
- Farm module / pptx
- start_both / stop_both scripts
- userconfig.xml
- Farm heartbeats (<farm>)
- Virtual IP address (<vip>)
- Farm's states in action
Troubleshooting
- Troubleshooting / pptx
- Analyze yourself the logs
- Take snapshots for support
- Boot / shutdown
- Web console / Command lines
- Mirror / Farm / Checkers
- Running an application without SafeKit
Support
- Evidian support / pptx
- Get permanent license key
- Register on support.evidian.com
- Call desk