Can anyone point me to the relevant documentation? Can’t find anything…
Istiod is created as a deployment in Kubernetes, so scaling out is done by increasing the number of replicas on the istiod deployment. However, check if you’re hitting the limits – as per docs, a single instance can support 1000 services (assuming you use the sidecar resource and isolate the namespaces). Istio / Performance and Scalability
You can modify the IstioOperator config and set an hpaSpec:
spec: components: pilot: enabled: true k8s: hpaSpec: minReplicas: 2
jlcrow is 100% correct.
You always want to set istiod replicas > 1, in production, for HA… However, do it all your other clusters too (dev/qa & sit), otherwise PodDisruptionBudgets will bite you during your Kubernetes upgrades. Ignore this warning at your own peril.