Setting an Environment Variable
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 CCE 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
- 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 a ConfigMap 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
- Log in to the CCE console. 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 ey1=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.