New Task: Exposing Pod Info ... Env Vars

_data/tasks.yml

@@ -14,6 +14,7 @@ toc:
   - docs/tasks/configure-pod-container/assign-cpu-ram-container.md
   - docs/tasks/configure-pod-container/configure-volume-storage.md
   - docs/tasks/configure-pod-container/configure-persistent-volume-storage.md
+  - docs/tasks/configure-pod-container/environment-variable-expose-pod-information.md
   - docs/tasks/configure-pod-container/distribute-credentials-secure.md
   - docs/tasks/configure-pod-container/pull-image-private-registry.md
   - docs/tasks/configure-pod-container/configure-liveness-readiness-probes.md

docs/tasks/configure-pod-container/dapi-envars-container.yaml

@@ -0,0 +1,45 @@
+apiVersion: v1
+kind: Pod
+metadata:
+  name: dapi-envars-resourcefieldref
+spec:
+  containers:
+    - name: test-container
+      image: gcr.io/google_containers/busybox:1.24
+      command: [ "sh", "-c"]
+      args:
+      - while true; do
+          echo -en '\n';
+          printenv MY_CPU_REQUEST MY_CPU_LIMIT;
+          printenv MY_MEM_REQUEST MY_MEM_LIMIT;
+          sleep 10;
+        done;
+      resources:
+        requests:
+          memory: "32Mi"
+          cpu: "125m"
+        limits:
+          memory: "64Mi"
+          cpu: "250m"
+      env:
+        - name: MY_CPU_REQUEST
+          valueFrom:
+            resourceFieldRef:
+              containerName: test-container
+              resource: requests.cpu
+        - name: MY_CPU_LIMIT
+          valueFrom:
+            resourceFieldRef:
+              containerName: test-container
+              resource: limits.cpu
+        - name: MY_MEM_REQUEST
+          valueFrom:
+            resourceFieldRef:
+              containerName: test-container
+              resource: requests.memory
+        - name: MY_MEM_LIMIT
+          valueFrom:
+            resourceFieldRef:
+              containerName: test-container
+              resource: limits.memory
+  restartPolicy: Never

docs/tasks/configure-pod-container/dapi-envars-pod.yaml

@@ -0,0 +1,38 @@
+apiVersion: v1
+kind: Pod
+metadata:
+  name: dapi-envars-fieldref
+spec:
+  containers:
+    - name: test-container
+      image: gcr.io/google_containers/busybox
+      command: [ "sh", "-c"]
+      args:
+      - while true; do
+          echo -en '\n';
+          printenv MY_NODE_NAME MY_POD_NAME MY_POD_NAMESPACE;
+          printenv MY_POD_IP MY_POD_SERVICE_ACCOUNT;
+          sleep 10;
+        done;
+      env:
+        - name: MY_NODE_NAME
+          valueFrom:
+            fieldRef:
+              fieldPath: spec.nodeName
+        - name: MY_POD_NAME
+          valueFrom:
+            fieldRef:
+              fieldPath: metadata.name
+        - name: MY_POD_NAMESPACE
+          valueFrom:
+            fieldRef:
+              fieldPath: metadata.namespace
+        - name: MY_POD_IP
+          valueFrom:
+            fieldRef:
+              fieldPath: status.podIP
+        - name: MY_POD_SERVICE_ACCOUNT
+          valueFrom:
+            fieldRef:
+              fieldPath: spec.serviceAccountName
+  restartPolicy: Never

docs/tasks/configure-pod-container/environment-variable-expose-pod-information.md

@@ -0,0 +1,163 @@
+---
+title: Exposing Pod Information to Containers Through Environment Variables
+---
+
+{% capture overview %}
+
+This page shows how a Pod can use environment variables to expose information
+about itself to Containers running in the Pod. Environment variables can expose
+Pod fields and Container fields.
+
+There are two ways to expose Pod and Container fields to a running Container:
+environment variables and
+[DownwardAPIVolumeFiles](/docs/resources-reference/v1.5/#downwardapivolumefile-v1).
+Together, these two ways of exposing Pod and Container fields are called the
+*Downward API*.
+
+{% endcapture %}
+
+
+{% capture prerequisites %}
+
+{% include task-tutorial-prereqs.md %}
+
+{% endcapture %}
+
+
+{% capture steps %}
+
+## Using Pod fields as values for environment variables
+
+In this exercise, you create a Pod that has one Container. Here is the
+configuration file for the Pod:
+
+{% include code.html language="yaml" file="dapi-envars-pod.yaml" ghlink="/docs/tasks/configure-pod-container/dapi-envars-pod.yaml" %}
+
+In the configuration file, you can see five environment variables. The `env`
+field is an array of
+[EnvVars](/docs/resources-reference/v1.5/#envvar-v1).
+The first element in the array specifies that the `MY_NODE_NAME` environment
+variable gets its value from the Pod's `spec.nodeName` field. Similarly, the
+other environment variables get their names from Pod fields.
+
+**Note**: The fields in this example are Pod fields. They are not fields of the
+Container in the Pod.
+
+Create the Pod:
+
+```shell
+kubectl create -f http://k8s.io/docs/tasks/configure-pod-container/dapi-envars-pod.yaml
+```
+
+Verify that the Container in the Pod is running:
+
+```
+kubectl get pods
+```
+
+View the Container's logs:
+
+```
+kubectl logs dapi-envars-fieldref
+```
+
+The output shows the values of selected environment variables:
+
+```
+minikube
+dapi-envars-fieldref
+default
+172.17.0.4
+default
+```
+
+To see why these values are in the log, look at the `command` and `args` fields
+in the configuration file. When the Container starts, it writes the values of
+five environment variables to stdout. It repeats this every ten seconds.
+
+Next, get a shell into the Container that is running in your Pod:
+
+```
+kubectl exec -it dapi-envars-fieldref -- sh
+```
+
+In your shell, view the environment variables:
+
+```
+/# printenv
+```
+
+The output shows that certain environment variables have been assigned the
+values of Pod fields:
+
+```
+MY_POD_SERVICE_ACCOUNT=default
+...
+MY_POD_NAMESPACE=default
+MY_POD_IP=172.17.0.4
+...
+MY_NODE_NAME=minikube
+...
+MY_POD_NAME=dapi-envars-fieldref
+```
+
+## Using Container fields as values for environment variables
+
+In the preceding exercise, you used Pod fields as the values for environment
+variables. In this next exercise, you use Container fields as the values for
+environment variables. Here is the configuration file for a Pod that has one
+container:
+
+{% include code.html language="yaml" file="dapi-envars-container.yaml" ghlink="/docs/tasks/configure-pod-container/dapi-envars-container.yaml" %}
+
+In the configuration file, you can see four environment variables. The `env`
+field is an array of
+[EnvVars](/docs/resources-reference/v1.5/#envvar-v1).
+The first element in the array specifies that the `MY_CPU_REQUEST` environment
+variable gets its value from the `requests.cpu` field of a Container named
+`test-container`. Similarly, the other environment variables get their values
+from Container fields.
+
+Create the Pod:
+
+```shell
+kubectl create -f http://k8s.io/docs/tasks/configure-pod-container/dapi-envars-container.yaml
+```
+
+Verify that the Container in the Pod is running:
+
+```
+kubectl get pods
+```
+
+View the Container's logs:
+
+```
+kubectl logs dapi-envars-resourcefieldref
+```
+
+The output shows the values of selected environment variables:
+
+```
+1
+1
+33554432
+67108864
+```
+
+{% endcapture %}
+
+{% capture whatsnext %}
+
+* [Defining Environment Variables for a Container](/docs/tasks/configure-pod-container/define-environment-variable-container/)
+* [PodSpec](/docs/resources-reference/v1.5/#podspec-v1)
+* [Container](/docs/resources-reference/v1.5/#container-v1)
+* [EnvVar](/docs/resources-reference/v1.5/#envvar-v1)
+* [EnvVarSource](/docs/resources-reference/v1.5/#envvarsource-v1)
+* [ObjectFieldSelector](/docs/resources-reference/v1.5/#objectfieldselector-v1)
+* [ResourceFieldSelector](/docs/resources-reference/v1.5/#resourcefieldselector-v1)
+
+{% endcapture %}
+
+
+{% include templates/task.md %}