In my previous article, I presented some considerations to ponder when architecting High Availability with SAS Viya. This article covers more details about the actual capabilities and configuration settings of SAS Viya deployments for the 2020.1 and later releases.
As you can remember from the previous article, fault tolerance can be provided by availability capabilities that exist at multiple levels:
Let’s enter into more details about the default capabilities for each one.
Cloud providers guarantee, by default, the availability of many IAAS resources to a level that would have required careful design, high cost, and complex maintenance to any on-prem data center just a few years ago.
Using a computing node (virtual machine) as an example, an individual VM underpinning an AKS cluster on Azure can guarantee an SLA of 99.9% without any special configuration (source: https://docs.microsoft.com/en-us/azure/architecture/high-availability/building-solutions-for-high-av...). This means less than 45 minutes of downtime per month!
Using cloud-provided storage for Persistent Volumes can also guarantee a default SLA level for your data and configuration files, depending on the chosen storage provider.
To achieve even better resilience, it is possible to deploy your Kubernetes cluster across multiple zones (in the same region) to protect it from data center outages. You can choose to spread across multiple zones only the managed Kubernetes control plane, only the nodes, or both. Control plane availability impacts the capability to control, monitor, and configure your cluster (including starting/stopping/scaling resources); nodes availability impacts SAS Viya availability.
While multi-zone clusters can improve availability for end-users, they may come with additional considerations:
Kubernetes provides multiple artifacts and automations that impact the availability of your applications, and SAS Viya 2020.1 has been designed to take native advantage of many.
SAS Viya servers and services can be clustered to increase their availability. With clustering, if a member of the cluster goes down, the surviving ones keep servicing client requests. Stateful services are configured for High Availability by default at initial deployment. By default, your SAS Viya environment starts with:
CAS High Availability can be enabled by choosing to deploy across several nodes (MPP) and with a backup controller – as was discussed in a previous article.
An optional Kustomize transformer can be used to enable two replicas for the stateless microservices.
In a similar way, another Kustomize transformer can configure a highly-available cluster for Open Distro for Elasticsearch, as described in this article.
Do not forget that your environment has dependencies on additional software that can be running in other namespaces in the same cluster as SAS Viya. For example, software like cert-manager, NGINX Ingress Controller, and the SAS Viya Monitoring solution for Kubernetes might be critical to the availability of SAS Viya and may have been deployed by default with single replicas, making them less highly available than SAS Viya itself. To increase the availability of these additional software solutions, consult their documentation for more information.
SAS Viya integration with cloud platforms is not a simple lift and shift of previous technologies. You can get real benefits from the capabilities provided at multiple levels by infrastructure services, platform components, and deployed applications, to provide end-users a better experience while managing costs and complexity.
Find more articles from SAS Global Enablement and Learning here.
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