Feature Request: Add SwapDetected Condition

[ajaysundark]

Historically, running Kubernetes with swap enabled has been discouraged. However, with support for swap is looking to GA in 1.34, it is important for cluster administrators to have clear visibility into which nodes have swap configured.

This proposal suggests a custom-plugin for introduction of a new NodeCondition called SwapDetected. This permanent condition would be set to True when swap memory is configured and active on a Kubernetes node.

The proposed approach involves:

1. bash script to check for active swap by examining the output of free -h command or by reading /proc/swaps.
2. config file that defines the SwapDetected permanent condition and rule to run the script at a regular interval (5s).

[SergeyKanzhelev]

I would ask the same question as in kubernetes/enhancements#5425. Let's have a coherent story with kubernetes/enhancements#5424.

I think there are also metrics on swap size that can be used for the same? Or I am wrong?

[ajaysundark]

I would ask the same question as in kubernetes/enhancements#5425. Let's have a coherent story with kubernetes/enhancements#5424.

I think there are also metrics on swap size that can be used for the same? Or I am wrong?

It's not clear to me what is in focus for KEP-5424. It's marked only as a placeholder for swap scheduling.

This is unrelated to scheduling but intends to add visibility when there's a swap configuration on the underlying hardware.

There's node.systemInfo.swap that gives available swap capacity at the node, when the configuration is LimitedSwap. NoSwap will show this as 0 even when there's a swap device configured. Agree it could be a lesser concerning scenario for swap in K8s, so this is not urgent to consider now.