Allow almost all printable ASCII characters in environment variables

Author: HirazawaUi

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

@@ -205,6 +205,42 @@ ConfigMaps consumed as environment variables are not updated automatically and r
 A container using a ConfigMap as a [subPath](/docs/concepts/storage/volumes#using-subpath) volume mount will not receive ConfigMap updates.
 {{< /note >}}
 
+
+### Using Configmaps as environment variables
+
+To use a Configmap in an {{< glossary_tooltip text="environment variable" term_id="container-env-variables" >}}
+in a Pod:
+
+1. For each container in your Pod specification, add an environment variable
+   for each Configmap key that you want to use to the
+   `env[].valueFrom.configMapKeyRef` field.
+1. Modify your image and/or command line so that the program looks for values
+   in the specified environment variables.
+
+This is an example of defining a ConfigMap as a pod environment variable:
+```yaml
+apiVersion: v1
+kind: Pod
+metadata:
+  name: env-configmap
+spec:
+  containers:
+  - name: envars-test-container
+    image: nginx
+    env:
+    - name: CONFIGMAP_USERNAME
+      valueFrom:
+        configMapKeyRef:
+          name: myconfigmap
+          key: username
+
+```
+
+#### Invalid environment variables {#restriction-env-from-invalid}
+
+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).
+
 ## Immutable ConfigMaps {#configmap-immutable}
 
 {{< feature-state for_k8s_version="v1.21" state="stable" >}}

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

@@ -566,23 +566,8 @@ For instructions, refer to
 
 #### Invalid environment variables {#restriction-env-from-invalid}
 
-If your environment variable definitions in your Pod specification are
-considered to be invalid environment variable names, those keys aren't made
-available to your container. The Pod is allowed to start.
-
-Kubernetes adds an Event with the reason set to `InvalidVariableNames` and a
-message that lists the skipped invalid keys. The following example shows a Pod that refers to a Secret named `mysecret`, where `mysecret` contains 2 invalid keys: `1badkey` and `2alsobad`.
-
-```shell
-kubectl get events
-```
-
-The output is similar to:
-
-```
-LASTSEEN   FIRSTSEEN   COUNT     NAME            KIND      SUBOBJECT                         TYPE      REASON
-0s         0s          1         dapi-test-pod   Pod                                         Warning   InvalidEnvironmentVariableNames   kubelet, 127.0.0.1      Keys [1badkey, 2alsobad] from the EnvFrom secret default/mysecret were skipped since they are considered invalid environment variable names.
-```
+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).
 
 ### Container image pull Secrets {#using-imagepullsecrets}
 

content/en/docs/reference/command-line-tools-reference/feature-gates/relaxed-environment-variable-validation.md

@@ -0,0 +1,13 @@
+---
+title: RelaxedEnvironmentVariableValidation
+content_type: feature_gate
+_build:
+  list: never
+  render: false
+
+stages:
+  - stage: alpha
+    defaultValue: false
+    fromVersion: "1.30"
+---
+Allow almost all printable ASCII characters in environment variables.

content/en/docs/tasks/inject-data-application/define-environment-variable-container.md

@@ -35,6 +35,11 @@ The `env` and `envFrom` fields have different effects.
 You can read more about [ConfigMap](/docs/tasks/configure-pod-container/configure-pod-configmap/#configure-all-key-value-pairs-in-a-configmap-as-container-environment-variables)
 and [Secret](/docs/tasks/inject-data-application/distribute-credentials-secure/#configure-all-key-value-pairs-in-a-secret-as-container-environment-variables).
 
+The character range of the environment variable name can be seen in
+[Environment variables names](/docs/concept/configuration/environment/environment-variables-names)
+If the `RelaxedEnvironmentVariableValidation` [feature gate](/docs/reference/command-line-tools-reference/feature-gates/) is enabled,
+all [printable ASCII characters](https://www.ascii-code.com/characters/printable-characters) except "=" may be used for environment variable names.
+
 This page explains how to use `env`.
 
 In this exercise, you create a Pod that runs one container. The configuration
@@ -102,6 +107,11 @@ Honorable`, and `Kubernetes`, respectively. The environment variable
 `MESSAGE` combines the set of all these environment variables and then uses it 
 as a CLI argument passed to the `env-print-demo` container.
 
+Environment variable names consist of letters, numbers, underscores, 
+dots, or hyphens, but the first character cannot be a digit.
+If the `RelaxedEnvironmentVariableValidation` [feature gate](/docs/reference/command-line-tools-reference/feature-gates/) is enabled,
+all [printable ASCII characters](https://www.ascii-code.com/characters/printable-characters) except "=" may be used for environment variable names.
+
 ```yaml
 apiVersion: v1
 kind: Pod