Scenario

An environment variable is a variable whose value can affect the way a running container will behave. You can modify environment variables even after workloads are deployed, increasing flexibility in workload configuration.

The function of setting environment variables on UCS is the same as that of specifying ENV in a Dockerfile.

After a container is started, do not modify configurations in the container. If configurations in the container are modified (for example, passwords, certificates, and environment variables of a containerized application are added to the container), the configurations will be lost after the container restarts and container services will become abnormal. An example scenario of container restart is pod rescheduling due to node anomalies.

Configurations must be imported to a container as arguments. Otherwise, configurations will be lost after the container restarts.

Environment variables can be set in the following modes:

Custom: Enter a variable name and value.
Added from ConfigMap: Import all keys in a ConfigMap as environment variables.
Added from ConfigMap key: Import a key in a ConfigMap as the value of an environment variable. For example, if you import configmap_value of configmap_key in ConfigMap configmap-example as the value of environment variable key1, an environment variable named key1 with its value is configmap_value exists in the container.
Added from secret: Import all keys in a secret as environment variables.
Added from secret key: Import the value of a key in a secret as the value of an environment variable. For example, if you import secret_value of secret_key in secret secret-example as the value of environment variable key2, an environment variable named key2 with its value secret_value exists in the container.
Variable Value/Reference: Use the field defined by a pod as the value of the environment variable, for example, the pod name.
Resource Reference: Use the field defined by a container as the value of the environment variable, for example, the CPU limit of the container.

Adding Environment Variables

When creating a workload, select Environment Variables under Container Settings.
Set environment variables.

YAML Example

apiVersion: apps/v1
kind: Deployment
metadata:
  name: env-example
  namespace: default
spec:
  replicas: 1
  selector:
    matchLabels:
      app: env-example
  template:
    metadata:
      labels:
        app: env-example
    spec:
      containers:
        - name: container-1
          image: nginx:alpine
          imagePullPolicy: Always
          resources:
            requests:
              cpu: 250m
              memory: 512Mi
            limits:
              cpu: 250m
              memory: 512Mi
          env:
            - name: key                     # Custom
              value: value
            - name: key1                    # Added from ConfigMap key
              valueFrom:
                configMapKeyRef:
                  name: configmap-example
                  key: key1
            - name: key2                    # Added from secret key
              valueFrom:
                secretKeyRef:
                  name: secret-example
                  key: key2
            - name: key3                    # Variable reference, which uses the field defined by a pod as the value of the environment variable.
              valueFrom:
                fieldRef:
                  apiVersion: v1
                  fieldPath: metadata.name
            - name: key4                    # Resource reference, which uses the field defined by a container as the value of the environment variable.
              valueFrom:
                resourceFieldRef:
                  containerName: container1
                  resource: limits.cpu
                  divisor: 1
          envFrom:
            - configMapRef:                 # Added from ConfigMap
                name: configmap-example
            - secretRef:                    # Added from secret
                name: secret-example
      imagePullSecrets:
        - name: default-secret

Viewing Environment Variables

If the contents of configmap-example and secret-example are as follows:

$ kubectl get configmap configmap-example -oyaml
apiVersion: v1
data:
  configmap_key: configmap_value
kind: ConfigMap
...

$ kubectl get secret secret-example -oyaml
apiVersion: v1
data:
  secret_key: c2VjcmV0X3ZhbHVl              # c2VjcmV0X3ZhbHVl is the value of secret_value in Base64 mode.
kind: Secret
...

The environment variables in the pod are as follows:

$ kubectl get pod
NAME                           READY   STATUS    RESTARTS   AGE
env-example-695b759569-lx9jp   1/1     Running   0          17m

$ kubectl exec env-example-695b759569-lx9jp  -- printenv
/ # env
key=value                             # Custom environment variable
key1=configmap_value                  # Added from ConfigMap key
key2=secret_value                     # Added from secret key
key3=env-example-695b759569-lx9jp     # metadata.name defined by the pod
key4=1                                # limits.cpu defined by container1. The value is rounded up, in unit of cores.
configmap_key=configmap_value         # Added from ConfigMap. The key value in the original ConfigMap key is directly imported.
secret_key=secret_value               # Added from key. The key value in the original secret is directly imported.

Setting Environment Variables

Scenario

Adding Environment Variables

YAML Example

Viewing Environment Variables