So before I used kubernetes the general rule I used for running multiple express instances on a VM was one per cpu. That seemed to give the best performance. For kubernetes, would it be wise to have a replica per node cpu? Or should I let the horizontalpodautoscaler decide? The cluster has a node autoscaler. Thanks for any advice!
good question !
You need to consider 4 things :
Run the pod using Deployment so you enable replication, rolling update,...so on
Set resources.limits to your container definition. this is mandatory for autoscaling , because HPA is monitoring the percentage of usage, and if there is NO limit, there will be NEVER percentage, then HPA will never reach the threshold.
Set resources.requests. This will help the scheduler to estimate how much the app needs, so it will be assigned to the suitable Node per its current capacity.
Set HPA threshold: The percentage of usage (CPU, memory) when the HPA will trigger scale out or scale in.
for your situation, you said "one per cpu".. then, it should be:
containers:
- name: express
image: myapp-node
#.....
resources:
requests:
memory: "256Mi"
cpu: "750m"
limits:
memory: "512Mi"
cpu: "1000m" # <-- 🔴 match what you have in the legacy deployment
you may wonder why I put memory limits/requests without any input from your side ? The answer is that I put it randomly. Your task is to monitor your application, and adjust all these values accordingly.