在文件 docker 容器中使用环境变量

Question

I am setting an environment variable in a docker container whose value I receive at run time.

  env:
    - name: POD_INFO
      value: {{ Values.resolved_when_the_container_starts }}

I want to use this value inside an XML file. Is there a way I can do this?

Something like

<property>
   <name>pod.info</name>
   <value>this place should pick up the value from that environment variable</value>
</property>

Answer 1

Neither Kubernetes nor Helm provide a way to template ConfigMaps or any other files. What you're probably looking for is init container , which starts before your container and which can execute any custom script you want. Then, you can modify the configuration file with your environment variable.

Answer 2

You could use envsubst and call it in your entrypoint.sh script. You will have to define your variable first and then substitute them with envsubst .

kminehart explaines very well how envsubst works in one of the github cases .

# mytemplate.tmpl  
apiVersion: extensions/v1beta1  
kind: Deployment  
# ...  
architecture: ${GOOS}  

GOOS=amd64 envsubst < mytemplate.tmpl > mydeployment.yaml  

# mydeployment.yaml  
apiVersion: extensions/v1beta1  
kind: Deployment  
# ...  
architecture: amd64  

Another way of env substition is sed . Here is a good article that shows how it works.

sed -i -g "s/[target_expression]/[replace_expression/g" <file>