Replacing properties file in container using configmaps in kubernetes - kubernetes

Question

I am trying to replace properties file in container using configMap and volumeMount in deployment.yaml file.
Below is my deployment file:
apiVersion: apps/v1
kind: Deployment
metadata:
name: deployment-properties
spec:
selector:
matchLabels:
app: agent-2
replicas: 2
template:
metadata:
labels:
app: agent-2
spec:
containers:
- name: agent-2
image: agent:latest
ports:
- containerPort: 8080
volumeMounts:
- mountPath: "/usr/local/tomcat/webapps/agent/WEB-INF/classes/conf/application.properties"
name: "applictaion-conf"
subPath: "application.properties"
volumes:
- name: applictaion-conf
configMap:
name: dddeagent-configproperties
items:
- key: "application.properties"
path: "application.properties"
Below is snippet from configMap:
apiVersion: v1
kind: ConfigMap
metadata:
name: agent-configp
data:
application.properties: |-
AGENT_HOME = /var/ddeagenthome
LIC_MAXITERATION=5
LIC_MAXDELAY=10000
After deployment, complete folder structure is getting mounted instead of single file. Because of which all the files are getting deleted from existing folder.
Version - 1.21.13

Answer 1

I checked this configuration and there are few misspelling. You are referring to config map "dddeagent-configproperties" but you have defined a ConfigMap object named as "agent-configp".
configMap: name: dddeagent-configproperties
Should be:
configMap: name: agent-configp
Besides that there a few indentation errors, so I will paste a fixed files at the end of the answer.
To the point of your question: your approach is correct and as I tested in my setup everything was working properly without any issues. I created a sample pod with mounted the ConfigMap the same way you are doing it (in the directory where there are other files). The ConfigMap was mounted as a file as it should and other files were still available in the directory.
Mounts:
/app/upload/test-folder/file-1 from application-conf (rw,path="application.properties")
Your approach is the same as described here.
Please double check that on the pod without mounted config map the directory /usr/local/tomcat/webapps/agent/WEB-INF/classes/conf really exists and other files are here. As your image is not public avaiable, I checked with the tomcat image and /usr/local/tomcat/webapps/ directory is empty. Note that even if this directory is empty, the Kubernetes will create agent/WEB-INF/classes/conf directories and application.properties file here, when you want to mount a file.
Fixed deployment and ConfigMap files with good indentation and without misspellings:
Deployment file:
apiVersion: apps/v1
kind: Deployment
metadata:
name: deployment-properties
spec:
selector:
matchLabels:
app: agent-2
replicas: 2
template:
metadata:
labels:
app: agent-2
spec:
containers:
- name: agent-2
image: agent:latest
ports:
- containerPort: 8080
volumeMounts:
- mountPath: "/usr/local/tomcat/webapps/agent/WEB-INF/classes/conf/application.properties"
name: "application-conf"
subPath: "application.properties"
volumes:
- name: application-conf
configMap:
name: agent-configp
items:
- key: "application.properties"
path: "application.properties"
Config file:
apiVersion: v1
kind: ConfigMap
metadata:
name: agent-configp
data:
application.properties: |-
AGENT_HOME = /var/ddeagenthome
LIC_MAXITERATION=5
LIC_MAXDELAY=1000