[Solved] You want to deploy multiple replicas of a pod with label app: cache so that no two pods run on the same node, but you want the scheduler to try to keep... Which affinity configuration achieves this? | Kubernetes

Kubernetes - Scheduling

You want to deploy multiple replicas of a pod with label app: cache so that no two pods run on the same node, but you want the scheduler to try to keep pods in the same zone if possible. Which affinity configuration achieves this?

A

Use <code>podAffinity</code> with <code>requiredDuringSchedulingIgnoredDuringExecution</code> on <code>app: cache</code> and <code>topologyKey: kubernetes.io/hostname</code> only

B

Use <code>podAntiAffinity</code> with <code>requiredDuringSchedulingIgnoredDuringExecution</code> on <code>app: cache</code> and <code>topologyKey: kubernetes.io/hostname</code>, plus <code>podAffinity</code> with <code>preferredDuringSchedulingIgnoredDuringExecution</code> on <code>topologyKey: failure-domain.beta.kubernetes.io/zone</code>

C

Use <code>podAntiAffinity</code> with <code>preferredDuringSchedulingIgnoredDuringExecution</code> on <code>app: cache</code> and <code>topologyKey: kubernetes.io/hostname</code> only

D

Use <code>podAffinity</code> with <code>preferredDuringSchedulingIgnoredDuringExecution</code> on <code>app: cache</code> and <code>topologyKey: failure-domain.beta.kubernetes.io/zone</code> only

Step-by-Step Solution

Solution:

Step 1: Prevent pods on same node strictly
Use podAntiAffinity with requiredDuringSchedulingIgnoredDuringExecution and topologyKey: kubernetes.io/hostname to ensure no two pods run on the same node.
Step 2: Prefer pods in same zone
Add podAffinity with preferredDuringSchedulingIgnoredDuringExecution and topologyKey: failure-domain.beta.kubernetes.io/zone to encourage scheduling pods in the same zone but not strictly.
Step 3: Combine both rules
Use podAntiAffinity with requiredDuringSchedulingIgnoredDuringExecution on app: cache and topologyKey: kubernetes.io/hostname, plus podAffinity with preferredDuringSchedulingIgnoredDuringExecution on topologyKey: failure-domain.beta.kubernetes.io/zone combines strict anti-affinity on node and preferred affinity on zone, matching the requirement.
Final Answer:
Use required podAntiAffinity on hostname and preferred podAffinity on zone -> Option B
Quick Check:
Strict anti-affinity + preferred affinity = Use podAntiAffinity with requiredDuringSchedulingIgnoredDuringExecution on app: cache and topologyKey: kubernetes.io/hostname, plus podAffinity with preferredDuringSchedulingIgnoredDuringExecution on topologyKey: failure-domain.beta.kubernetes.io/zone [OK]

Quick Trick: Use required anti-affinity on node + preferred affinity on zone [OK]

Common Mistakes:

Using affinity instead of anti-affinity to separate pods
Using preferred instead of required for strict separation
Ignoring zone preference

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Which affinity configuration achieves this?

Step 1: Prevent pods on same node strictly

Step 2: Prefer pods in same zone

Step 3: Combine both rules

Final Answer:

Quick Check:

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