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A Filter plugin is two methods and a string

Claim — the smallest working scheduler plugin in the tree is under fifty lines including the licence header, and the thing that makes it a plugin is not a base class, a registration annotation or a lifecycle: it is that it satisfies an interface and appears in a map.

Rests on — the default set. You have the list of what runs; this is the shape of one of them, and it is the shape build artifact 2 must reproduce from outside the tree.

Topology — none.

Do

  1. Read all three of the tiny filters end to end. They are item 7 of the area and the whole point of assigning three is that the third one is boring:
wc -l pkg/scheduler/framework/plugins/nodename/*.go \
      pkg/scheduler/framework/plugins/nodeunschedulable/*.go \
      pkg/scheduler/framework/plugins/tainttoleration/*.go | grep -v _test
cat pkg/scheduler/framework/plugins/nodeunschedulable/node_unschedulable.go

  1. For each, write down four things: the Name() string, the interfaces it satisfies, the exact condition under which it returns a refusal, and which refusal code it uses. Two of the three refuse in a way that means "this will never work for this pod as written"; note which and why that is the correct choice there.

  2. Find the rejection message each one produces — the human-readable string, not the code. Grep for it as a literal:

grep -rn 'ErrReason' pkg/scheduler/framework/plugins/nodeunschedulable/ pkg/scheduler/framework/plugins/tainttoleration/

Those strings are what a pod's event will say. Write them down verbatim; the next exercise produces them on a live cluster and the comparison is the check.

  1. Answer the phase's question: what would you have to add to one of these files to make it also score nodes? Do not write it — name the interface and the method signature.

Expect — three files where the largest is dominated by the taint-matching helper and the smallest is almost entirely the struct, the Name() and one if. Expect the refusal codes to differ between the three, and expect that difference to line up exactly with the queue behaviour you will meet in module 5.4: a pod refused as unresolvable does not get retried on the same trigger as one refused as merely unschedulable.

Write down — the four-item description of each plugin, the three verbatim rejection strings, and the one-line answer to the scoring question.

Footprint note — reading only. This is the last exercise before the phase's first cluster.

Teardown — nothing created. No topology to release — the next exercise provisions one.