Add envFrom details in docs (#47709)

* Add envFrom details in docs

* Add envFrom details in docs

* deleted command prompt

* Update content/en/docs/concepts/configuration/configmap.md

Co-authored-by: Andrii Holovin <Andygol@users.noreply.github.com>

* Update content/en/docs/concepts/configuration/configmap.md

Co-authored-by: Andrii Holovin <Andygol@users.noreply.github.com>

* Update content/en/docs/concepts/configuration/configmap.md

Co-authored-by: Andrii Holovin <Andygol@users.noreply.github.com>

* Update content/en/docs/concepts/configuration/configmap.md

Co-authored-by: Andrii Holovin <Andygol@users.noreply.github.com>

* Update content/en/docs/concepts/configuration/configmap.md

Co-authored-by: Andrii Holovin <Andygol@users.noreply.github.com>

* Update content/en/docs/concepts/configuration/configmap.md

Co-authored-by: Andrii Holovin <Andygol@users.noreply.github.com>

* Update content/en/docs/concepts/configuration/configmap.md

Co-authored-by: Andrii Holovin <Andygol@users.noreply.github.com>

* Update content/en/docs/concepts/configuration/configmap.md

Co-authored-by: Tim Bannister <tim@scalefactory.com>

* Update content/en/docs/concepts/configuration/configmap.md

Co-authored-by: Tim Bannister <tim@scalefactory.com>

* Update content/en/docs/concepts/configuration/configmap.md

Co-authored-by: Tim Bannister <tim@scalefactory.com>

* added shortcode

* Update content/en/docs/concepts/configuration/configmap.md

Co-authored-by: Qiming Teng <tengqm@outlook.com>

* Update content/en/docs/concepts/configuration/configmap.md

Co-authored-by: Qiming Teng <tengqm@outlook.com>

* Update content/en/docs/concepts/configuration/configmap.md

Co-authored-by: Qiming Teng <tengqm@outlook.com>

* Update content/en/docs/concepts/configuration/configmap.md

Co-authored-by: Qiming Teng <tengqm@outlook.com>

* Update content/en/docs/concepts/configuration/configmap.md

Co-authored-by: Qiming Teng <tengqm@outlook.com>

* Update content/en/docs/concepts/configuration/configmap.md

Co-authored-by: Qiming Teng <tengqm@outlook.com>

* Update content/en/docs/concepts/configuration/configmap.md

Co-authored-by: Qiming Teng <tengqm@outlook.com>

* Accept review comments

---------

Co-authored-by: Andrii Holovin <Andygol@users.noreply.github.com>
Co-authored-by: Tim Bannister <tim@scalefactory.com>
Co-authored-by: Qiming Teng <tengqm@outlook.com>

content/en/docs/concepts/configuration/configmap.md

@@ -221,6 +221,54 @@ in a Pod:
    in the specified environment variables.
 
 This is an example of defining a ConfigMap as a pod environment variable:
+
+The following ConfigMap (myconfigmap.yaml) stores two properties: username and access_level:
+
+```yaml
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: myconfigmap
+data:
+  username: k8s-admin
+  access_level: "1"
+```
+
+The following command will create the ConfigMap object:
+
+```shell
+kubectl apply -f myconfigmap.yaml
+```
+
+The following Pod consumes the content of the ConfigMap as environment variables:
+
+{{% code_sample file="configmap/env-configmap.yaml" %}}
+
+The `envFrom` field instructs Kubernetes to create environment variables from the sources nested within it.
+The inner `configMapRef` refers to a ConfigMap by its name and selects all its key-value pairs.
+Add the Pod to your cluster, then retrieve its logs to see the output from the printenv command.
+This should confirm that the two key-value pairs from the ConfigMap have been set as environment variables:
+
+```shell
+kubectl apply -f env-configmap.yaml
+```
+```shell
+kubectl logs pod/ env-configmap
+```
+The output is similar to this:
+```console
+...
+username: "k8s-admin"
+access_level: "1"
+...
+```
+
+Sometimes a Pod won't require access to all the values in a ConfigMap.
+For example, you could have another Pod which only uses the username value from the ConfigMap.
+For this use case, you can use the `env.valueFrom` syntax instead, which lets you select individual keys in
+a ConfigMap. The name of the environment variable can also be different from the key within the ConfigMap.
+For example:
+
 ```yaml
 apiVersion: v1
 kind: Pod
@@ -236,9 +284,13 @@ spec:
         configMapKeyRef:
           name: myconfigmap
           key: username
-
 ```
 
+In the Pod created from this manifest, you will see that the environment variable
+`CONFIGMAP_USERNAME` is set to the value of the `username` value from the ConfigMap.
+Other keys from the ConfigMap data are not copied into the environment.
+
+
 It's important to note that the range of characters allowed for environment
 variable names in pods is [restricted](/docs/tasks/inject-data-application/define-environment-variable-container/#using-environment-variables-inside-of-your-config).
 If any keys do not meet the rules, those keys are not made available to your container, though

content/en/examples/configmap/env-configmap.yaml

@@ -0,0 +1,12 @@
+apiVersion: v1
+kind: Pod
+metadata:
+  name: env-configmap
+spec:
+  containers:
+    - name: app
+      command: ["/bin/sh", "-c", "printenv"]
+      image: busybox:latest
+      envFrom:
+        - configMapRef:
+            name: myconfigmap