mirror of https://github.com/k3s-io/k3s
51 lines
1.7 KiB
Markdown
51 lines
1.7 KiB
Markdown
# Downward API
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The downward API allows containers to consume information about the system without coupling to the
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kubernetes client or REST API.
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### Capabilities
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Containers can consume the following information via the downward API:
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* Their pod's name
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* Their pod's namespace
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### Consuming information about a pod in a container
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Containers consume information from the downward API using environment variables. In the future,
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containers will also be able to consume the downward API via a volume plugin. The `valueFrom`
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field of an environment variable allows you to specify an `ObjectFieldSelector` to select fields
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from the pod's definition. The `ObjectFieldSelector` has an `apiVersion` field and a `fieldPath`
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field. The `fieldPath` field is an expression designating a field on the pod. The `apiVersion`
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field is the version of the API schema that the `fieldPath` is written in terms of. If the
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`apiVersion` field is not specified it is defaulted to the API version of the enclosing object.
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### Example: consuming the downward API
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This is an example of a pod that consumes its name and namespace via the downward API:
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```yaml
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apiVersion: v1beta3
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kind: Pod
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metadata:
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name: dapi-test-pod
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spec:
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containers:
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- name: test-container
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image: gcr.io/google_containers/busybox
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command: [ "/bin/sh", "-c", "env" ]
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env:
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- name: POD_NAME
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valueFrom:
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fieldRef:
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fieldPath: metadata.name
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- name: POD_NAMESPACE
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valueFrom:
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fieldRef:
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fieldPath: metadata.namespace
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restartPolicy: Never
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```
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[]()
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