Problem using dictionary in lieu of k8s.WeightedPodAffinityTerm

[LS80]

The following example produces a valid pod manifest

from constructs import Construct
from cdk8s import App, Chart

from imports import k8s

class MyChart(Chart):
    def __init__(self, scope: Construct, id: str):
        super().__init__(scope, id)

        k8s.KubePod(self, "pod",
            metadata=k8s.ObjectMeta(name="pod-affinity"),
            spec=k8s.PodSpec(
                affinity=k8s.Affinity(
                    pod_anti_affinity=dict(
                        preferred_during_scheduling_ignored_during_execution=[
                            k8s.WeightedPodAffinityTerm(
                                weight=100,
                                pod_affinity_term=dict(
                                    label_selector=dict(match_labels=dict(foo="bar")),
                                    topology_key="topology.kubernetes.io/zone"
                                )
                            )
                        ]
                    )
                ),
                containers=[
                    k8s.Container(
                        name="pod-affinity",
                        image="registry.k8s.io/pause:2.0"
                    )
                ],
            )
        )

app = App()
MyChart(app, "pod")

But using a dictionary in place of k8s.WeightedPodAffinityTerm produces an error Missing required properties for k8s.WeightedPodAffinityTerm: 'podAffinityTerm'.

from constructs import Construct
from cdk8s import App, Chart

from imports import k8s

class MyChart(Chart):
    def __init__(self, scope: Construct, id: str):
        super().__init__(scope, id)

        k8s.KubePod(self, "pod",
            metadata=k8s.ObjectMeta(name="pod-affinity"),
            spec=k8s.PodSpec(
                affinity=k8s.Affinity(
                    pod_anti_affinity=dict(
                        preferred_during_scheduling_ignored_during_execution=[
                            dict(
                                weight=100,
                                pod_affinity_term=dict(
                                    label_selector=dict(match_labels=dict(foo="bar")),
                                    topology_key="topology.kubernetes.io/zone"
                                )
                            )
                        ]
                    )
                ),
                containers=[
                    k8s.Container(
                        name="pod-affinity",
                        image="registry.k8s.io/pause:2.0"
                    )
                ],
            )
        )

app = App()
MyChart(app, "pod")

app.synth()

I assume it's an example of the issue discussed in aws/jsii#1919 (Passing dicts in lieu of jsii structs does not consistently work).

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[LS80]

@iliapolo is this something for the upstream https://github.com/aws/jsii to fix or can it be fixed here?

[iliapolo]

Interesting. This however does work:

from constructs import Construct
from cdk8s import App, Chart

from imports import k8s

class MyChart(Chart):
    def __init__(self, scope: Construct, id: str):
        super().__init__(scope, id)

        k8s.KubePod(self, "pod",
            metadata=k8s.ObjectMeta(name="pod-affinity"),
            spec=k8s.PodSpec(
                affinity=k8s.Affinity(
                    pod_anti_affinity=dict(
                        preferred_during_scheduling_ignored_during_execution=[
                            dict(
                                weight=100,
                                podAffinityTerm=dict(
                                    labelSelector=dict(match_labels=dict(foo="bar")),
                                    topologyKey="topology.kubernetes.io/zone"
                                )
                            )
                        ]
                    )
                ),
                containers=[
                    k8s.Container(
                        name="pod-affinity",
                        image="registry.k8s.io/pause:2.0"
                    )
                ],
            )
        )

app = App()
MyChart(app, "pod")

app.synth()

(Note the casing of properties inside the dict)

It looks like case conversion doesn't happen for literal dictionaries. It kind of makes sense because there's no apparent reason a literal dictionary should go through case conversion. jsii would have to detect that dictionary is being in lieu of a struct, right now it just passes it through. Definitely a jsii issue, i'll check with the team and update here.

Thanks for reporting!

[iliapolo]

So not much we can do here, the behavior here is explained in this issue (see Passing dict in lieu of jsii structs does not consistently work). Keeping this open for discoverability, but this will have to wait for a jsii fix.