Last modified November 22, 2018

Clusters Over Multiple Availability Zones

This is currently only available with Giant Swarm 6.1.0 on AWS

With Giant Swarm you can easily launch cluster across multiple availability zones (AZs). This will lower the risk that your cluster will get unavailable due to an incident in a particular AWS data center.

What availability zones are good for

Both AWS and Azure support AZs within their regions. These zones still have good interconnectivity but are separated from each other to isolate failures within one zone from the others. So it is more likely that one AZ goes down than the whole region. If your clusters are running within multiple AZs then Kubernetes can easily shift your workloads from one AZ into the other.

Your cluster nodes have labels that indicate in which availability zone they are running. You can influence the scheduling of your pods via node affinity and/or inter-pod affinity or anti-affinity.

This enables use cases such as

  • Running stateless services balanced over multiple AZs

  • Group certain services that talk a lot to each other together and make sure they always run together within the same availability zone.

  • Setup replication of your data across multiple AZs by keeping each instance of your StatefulSet in a different AZ.

Details you should know about

  • On AWS availability zones are randomized across accounts and there is no way to determine which AZ you are really in, based on the name. E.g. the zone eu-central-1a in the account of the cluster is not necessarily the same eu-central-1a in your account.

  • Availability zones get selected randomly by the Giant Swarm control plane. You only need to specify the number of availability zones.

  • Nodes will get distributed evenly across availability zones. There is currently no way to determine which or how many nodes should be started in a particular availability zone. But the nodes will have a label that indicates in which availability zone the node is running.

  • Single availability zone clusters start in a random availability zone too. This is a means to minimize the risk of all your clusters becoming unavailable due to a failure in one particular AZ.

  • Volumes can not be moved across availability zones. You need to take this into account once designing for high availability. If the AZ with your volume goes down, there will be no way to reschedule the pod to another availability zone. Either you need to create a new volume from a snapshot or you will have to replicate your data across AZs.

  • To make sure your pods and volumes end up on the same nodes, we recommend to specify WaitForFirstConsumer as volumeBindingMode in your storage classes. But your clusters come with a default storage class that contains this setting already. See Volume Binding Mode

Get started

You can create clusters in several ways:

When inspecting details of such a cluster, or using the gsctl show cluster command, we display the list of availability zones used by the cluster.

Further reading