Cloud platforms only protect applications from downtime caused by hardware failures. Mission critical applications require HA/DR protection regardless of the cloud environment they operate in.

When providing high availability protection, it is a general principle to ensure all components are redundant to avoid Single Points of Failure (SPOF). That is, ensure that no single element causes the entire system to stop if it fails. However, it is important to note that the operational infrastructure is hard to access in the public cloud.

In a cloud-based high availability cluster, there is a possibility that the standby node(s) will be located on the same host server, in the same rack, and using the same network switch as the operating node. Unless you configure these elements with redundancy, any of them could be a SPOF and put the application at risk for catastrophic failure.

It is necessary to ensure cluster nodes are on different cloud “regions” and “availability zones” that physically separate the data center and operational infrastructure in different geographic locations.

What are the main principles for ensuring availability in the cloud?

You cannot expect the various components that make up a physical IT infrastructure to operate according to specifications forever as parts wear out, systems become incompatible, and settings change. Although regular maintenance can reduce the risk of downtime, it’s likely that something will fail over the course of the product lifecycle.

In some rare cases, you may have a serious bug that is latent in the OS or embedded software that causes the application to stop working.

As you may have already noticed, the HA cluster configuration is exactly in line with this principle, and a single point of failure is eliminated by making the important server and its resources redundant to the active system (production system). However, it is important to remember two things: 1. the server hardware is not the only critical component and 2. other critical SPOF components may be invisible to you in a public cloud infrastructure.

Beware of the pitfalls of a single point of failure hidden in the cloud’s invisible infrastructure

Most public clouds operate in a so-called “multi-tenant” mode. That is, they run the VMs of multiple companies on the same physical host server. And with a regular contract, you can’t specify which host server your system runs on. This may cause problems as

the standby node in your cloud cluster may be placed on the same host server that operates the active node. Even if you configure an HA cluster configuration, if the host server goes down, the operating node and the standby node will both go down too. In this scenario, your cloud operator decides when and how your system will be restored.

The host server that operates the active node and the host server that operates the standby node may be in the same rack. In this case, the rack becomes a SPOF, so if a failure occurs there both the active and standby nodes under it will also fail.

Furthermore, in the upper layers of your infrastructure such as network switches that bundle multiple racks, gateways and routers, and power supply units in data centers, the operating system node and the standby system node may coexist in the same system, and if these key components aren’t redundant, then you have an inescapable single point of failure. Again, for a company that is a public cloud user, such a data center infrastructure is a black box, it may impossible to see into the detailed configuration to identify SPOFs.

Public cloud availability zones and regions should be leveraged for availability

How can we explicitly avoid hidden single points of failures in the public cloud? The most robust method is to use the “Availability Zones” and “Regions” prepared on the cloud side.

An Availability Zone is an independent physical separation of the infrastructure within your data center. And regions are independent data centers that are geographically separated. Public clouds allow you to deliberately use these Availability Zones or regions for different purposes.

By constructing an HA cluster configuration in which operating nodes and standby nodes are distributed in different availability zones across these two or more regions, almost all SPOFs can be avoided with certainty. If you adhere to these best practices, you can confidently ensure availability, DR (Disaster Recovery) and BCP (Business Continuity Planning).

Reproduced with permission from SIOS

How to Protect Applications and Databases

Every Application and Database Has Its Own Best Practices

Complex applications, databases and ERP systems have specific requirements for boot order, service module placement, and other requirements. Failing to adhere to these best practices can result in unreliable failover, application performance issues and other unexpected application behaviors after failover. SIOS’ unique application recovery kits provide application-specific intelligence to ensure clusters are configured accurately and that failovers maintain best practices.

Application Recovery Kits (ARKs)

Application Recovery Kits (ARKs) include tools and utilities that allow LifeKeeper to manage and control a specific application or service. When an ARK is installed for a specific application, LifeKeeper is able to monitor the health of the application and automatically recover the application if it fails. These Recovery Kits are non-intrusive and require no changes within the application in order for it to be protected by LifeKeeper.

There is a comprehensive library of ‘off-the-shelf’ Application Recovery Kits available as part of the SIOS Protection Suite portfolio. The types and quantity of ARKs supplied vary based on the edition of SIOS Protection Suite purchased.

To mitigate system downtime and ensure high availability for Windows, IT best practice recommends that you connect two or more servers (or nodes) and use clustering software. High availability clustering software monitors the health of the primary node and initiates recovery actions if it detects an issue. In the event of a failure, the secondary node needs to access the most current versions of data in storage. In traditional clusters, this is achieved by connecting all nodes of the clusters to the same shared storage or by using efficient, cluster-aware replication software to synchronize local storage on all cluster nodes.

The cluster nodes should be separated geographically to protect applications from sitewide and regional disasters.

You have several Windows clustering software options, including Microsoft Windows Server Failover Clustering, SIOS LifeKeeper for Windows, and others.

What is Window Clustering?

In a Windows environment, two or more nodes and shares the same storage. A third node is often configured as a “witness” server that designates the primary server if the connection between nodes is lost. In addition to monitoring the health of the cluster, the nodes work together to collectively provide:[1]

• Resource management – Individual nodes provide physical resources such as SAN and network interfaces. The hosted applications are registered as a cluster resource and can configure startup and health dependencies upon other resources.
• Failover coordination – Each resource is hosted on a primary node and can be automatically or manually transferred to one or more secondary nodes. Nodes and hosted applications are notified when failover occurs so that they can appropriately react. WSFC works with Microsoft Always On Availability Groups and Always On Failover Clustering to coordinate failover In Microsoft SQL Server environments.

How SIOS DataKeeper Complements WSFC

WSFC requires shared storage to ensure all cluster nodes are accessing the most up-to-date data in the event of a failover. Often, companies use expensive SAN hardware to assure data redundancy. SANs represent a single point of failure risk. And, if you want to run your application in the cloud with the same Windows Server Failover clustering protection, there is no SAN available.

SIOS DataKeeper Cluster Edition seamlessly integrates with and extends WSFC and SQL Server Always On Failover clustering by eliminating the need for shared storage. It provides performance-optimized, host-based replication to synchronize local storage in all cluster nodes, creating a SANless cluster. While WSFC manages the cluster, SIOS DataKeeper performs synchronous or asynchronous replication of the storage giving the standby nodes immediate access to the most current data in the event of a failover. SIOS DataKeeper not only eliminates the cost, complexity, and single-point-of-failure risk of a SAN, but also allows you to use the latest in fast PCIe Flash and SSD in your local storage for performance and protection in a single cost-efficient solution.

With SIOS DataKeeper, you can also balance network bandwidth and CPU utilization for each application.

• If fast replication is critical, SIOS DataKeeper can achieve more than 90 percent bandwidth utilization to accelerate data synchronization.
• If minimizing network impact is your top priority, SIOS DataKeeper offers integrated compression and bandwidth throttling.

In addition, SIOS DataKeeper’s Target Snapshots feature lets you run point-in-time reports from a secondary node to offload workloads that can impact performance on the primary node. This lets you query and run reports faster and make faster decisions.

Working with WSFC, SIOS DataKeeper Cluster Edition protects business-critical Windows environments, including Microsoft SQL Server, SAP, SharePoint, Lync, Dynamics, and Hyper-V using your choice of industry-standard hardware and local attached storage in a “shared-nothing” or SANless configuration.[2] SIOS DataKeeper also provides high availability and disaster recovery protection for your business-critical applications in cloud environments, such as Amazon Web Services (AWS), Microsoft Azure, and Google Cloud Services without sacrificing performance.

SIOS LifeKeeper for Windows – Protecting Windows Applications Without WSFC

SIOS LifeKeeper for Windows is a tightly integrated clustering solution that combines high availability failover clustering, continuous application monitoring, data replication, and configurable recovery policies to protect your business-critical applications and data from downtime and disasters.

Distributed metadata and notifications

The WSFC service and node’s metadata/status are hosted on each node in the cluster. When changes occur on any node, updated information is automatically replicated to all other nodes.

SIOS LifeKeeper for Windows monitors the health of the application environment, including servers, operating systems, and databases. It can stop and restart an application both locally and on another cluster server at the same site or in another location. When a problem is detected, SIOS LifeKeeper automatically performs the recovery actions and automatically manages cascading and prioritized failovers.

With SIOS LifeKeeper, you can use your choice of SAN or SANless clusters using a wide array of storage devices, including direct-attached storage, iSCSI, Fibre Channel, and more.

Popular SIOS Windows Clustering Solutions

Some of the most popular SIOS Windows clustering solutions – for SQL Server, SAP, and cloud-based environments – are discussed in more detail below.

Windows Clustering for SQL Server, SAP, and Oracle

SIOS provides comprehensive protection for both applications and data, including high availability, data replication, and disaster recovery. To protect SAP in a Windows environment, SIOS LifeKeeper monitors the entire application stack. SIOS protects your Oracle Database whether you are using it with SAP or running standalone Oracle applications – you simply select the Application Recovery Kit that matches your configuration.

Windows Clustering in the Cloud

Whether you need SIOS DataKeeper to enable Windows Server Failover Clustering in the cloud or SIOS LifeKeeper for Windows for application monitoring and failover orchestration, as well as efficient, block-level data replication, SIOS delivers complete configuration flexibility. SIOS allows you to create a cluster in any combination of physical, virtual, cloud, or hybrid cloud infrastructures. For example, working with WSFC, SIOS DataKeeper can:

• Protect critical on-premise or hybrid business applications to a high availability Windows environment in AWS, Azure, or Google Cloud.
• Protect cloud applications, such as SQL Server and SAP, by creating a Windows cluster in AWS, Azure, or Google Cloud.
• Provide site-wide, local, or regional high availability and disaster recovery protection by failing over application instances across cloud availability zones or regions.

SIOS DataKeeper Cluster Edition can provide high availability cluster protection across cloud

Protecting the Widest Range of Applications in the Industry

SIOS provides offerings that support a breadth of applications, operating systems, and infrastructure environments, providing a single solution that can handle all your high availability needs. Here are just a few examples that demonstrate the power of SIOS.

• Perth Stadium in Western Australia implemented SIOS DataKeeper with WSFC to provide high availability for their Hyper-V virtual machines.
• PayGo (paygoutilities.com), based in the U.S., implemented SIOS DataKeeper with WSFC to provide high availability for SQL Server on AWS.
• Toyo Gosei, based in Japan, implemented SIOS DataKeeper with WSFC to provide high availability and disaster recovery for their SAP application on Azure.

For more information on high availability/disaster recovery solutions to support your Windows environment click here [TM(1] .

References

[1] https://docs.microsoft.com/en-us/sql/sql-server/failover-clusters/windows/windows-server-failover-clustering-wsfc-with-sql-server?view=sql-server-ver15[2] A shared-nothing architecture (SN) is a distributed-computing architecture in which each update request is satisfied by a single node (processor/memory/storage unit). https://en.wikipedia.org/wiki/Shared-nothing_architecture

Reproduced with permission from SIOS

What is Linux Clustering?

A high availability Linux cluster is a group of Linux computers or nodes, storage devices that work together and are managed as a single system. In a traditional clustering configuration, two nodes are connected to shared storage (typically a SAN). With Linux clustering, an application is run on one node, and clustering software is used to monitor its operation. If the software detects an issue, it moves operation of the application to the secondary node in a process called failover. Since the secondary node shares storage with the primary, operation can continue quickly, meeting very short (seconds to minutes) recovery time and recovery point objectives.

Linux High Availability Clustering

Some Linux operating system vendors offer clustering software, such as SUSE Linux HAE; Red Hat Enterprise Linux (RHEL); and Oracle Real Application Clusters (RAC). While they allow you to create a failover cluster, they present a variety of challenges. First, choosing which software to use for each component of the HA configuration, which at a minimum, must include three related capabilities: data replication, server clustering and a resource manager with a heartbeat monitor. With SUSE and Red Hat, you are also locked into the OS. If you want to use other less expensive or free OS versions, such as CentOS or Oracle Enterprise Linux (OEL), you will need to buy a separate HA solution.

Whichever you choose, creating a Linux clustering solution with open source software for high availability is a “Do-It-Yourself” (DIY) project, that is highly manual and prone to human error.

Linux HA extensions require a high degree of technical skill, creating complexity and reliability issues that challenge most operators.

SUSE Linux Enterprise Server and Red Hat Enterprise Linux both solutions offer both a SAN and SANless environment but require that a replication software called DRBD be installed and configured in the OS to support data replication in the SANless environment. Unfortunately, this requires heavy custom scripting, which can take a long time to test and validate and requires retesting when any updates are made to the environment. Since these companies are operating system companies first and foremost, their support is geared towards operating system-level issues and often there is little to no HA expertise to help a customer with their issues.

Oracle RAC is a high availability solution, but it is primarily architected for the database management tier. This means you will need a different HA solution for those components that do the monitoring, management, and recovery of your application tiers. Oracle RAC is also very expensive – requiring you to upgrade to Oracle Enterprise Edition in addition to paying for the RAC option – typically hundreds of thousands of dollars – when compared to other Linux clustering solutions, such as SIOS Protection Suite.

SIOS LifeKeeper for Linux

The SIOS LifeKeeper for Linux provides a tightly integrated combination of high availability failover clustering, continuous application monitoring, data replication, and configurable recovery policies, protecting your business-critical applications from downtime and disasters. While SIOS LifeKeeper can operate in a SAN environment to support a traditional HA hardware-based cluster, the architecture takes a shared-nothing approach to server clustering allowing it to run SANless. It delivers a robust, versatile and easily configurable solution with automatic and manual failover/failback recovery policies for a wide variety of applications.

SIOS Protection Suite for Linux includes:

• SIOS LifeKeeper, which provides flexible failover clustering software that monitors the entire application stack
• SIOS DataKeeper, which provides fast, efficient host-based, block-level data replication for mirroring local storage in a SANless cluster configuration or replicating to remote locations or cloud for disaster recovery
• Multiple Application Recovery Kits (ARKs), with automated configuration and validation tools built into the product to protect your business-critical applications and data from downtime and disasters.

It is the SIOS’ team’s depth of knowledge in application recovery and the solution’s automation of application monitoring and recovery that makes it easier to use and a better, less expensive choice when compared to the Linux clustering solutions offered SUSE, Red Hat, and Oracle.

In addition, SIOS LifeKeeper supports all major Linux distributions, including Red Hat Enterprise Linux, SUSE Linux Enterprise Server, CentOS, and Oracle Linux and accommodates a wide range of storage architectures. SIOS software has been adapted and optimized to run on these operating systems and the components are tested so ensure the SANless cluster solution will work on each OS.

Lastly, with the SIOS Protection Suite for Linux, you can run your business-critical applications in a flexible, scalable cloud environment, such as Amazon Web Services (AWS) without sacrificing performance, high availability, or disaster protection.

Linux Clustering in AWS and Microsoft Azure

While cloud providers, such as AWS and Microsoft Azure, provide high availability options, they do not provide the level of high availability and breadth of protection across the whole application infrastructure that customers demand and that you once achieved by using clusters before cloud computing. That is why AWS is partnering with SIOS. SIOS Protection Suite for Linux achieves these desired levels of high availability for our mutual customers and the critical applications they are moving to the cloud.

SIOS LifeKeeper Linux provides all the elements you need to create a high availability Linux cluster in a virtual private cloud (VPC) within a single AWS or Azure Region across two Availability Zones. It also supports out-of-the-box protection for SAP systems, Oracle databases, and other business-critical applications.

SIOS LifeKeeper Quick Start Guide for AWS

A Quick Start, available in the AWS Marketplace for enterprise users who want to deploy SIOS LifeKeeper for Linux on AWS into their test or production environment. The SIOS Protection Suite Quickstart on the AWS Marketplace helps you create a fully configured and operational Linux high availability cluster in a few short steps. It sets up an AWS architecture for SIOS LifeKeeper for Linux and deploys it into your AWS account in about half an hour.