Helm Deployment of multiple microservices with single configmap - kubernetes-helm

Question

we are deploying multiple microservices using helm charts but all those microservices are using one shared objects such as configmap.
Requirement should be when we do helm deployment microservices will be installed/upgraded using "helm upgrade --install", but it should not try to deploy shared configmap for all the microservice.
Shared configmap has to be deployed only once but all the microservices has to use that shared configmap, how can we achieve this with helm and what will be the helm structure and concepts for my case.

Answer 1

Please be more specific in your question, you are deploying each of you ms separately?
Let's suppose you have 3 ms - A, B and C. If you want to use shared config map for all of those, so you have next options:
Create top level chart, which includes A, B and C sub charts, as well as configmap definition. This way when you deploy your TLC, config map will be created once.
If you need to deploy each chart independently, in this case create separate chart which includes only config map, deploy it first, and then deploy all A, B and C charts.
Upd.
Example of how you can perform lookup and check if resource exists, and based on this create or not create.
{{- $secretName:= (tpl .Values.your.secret.secretName .)}}
{{- $secret:= (lookup "v1" "Secret" .Release.Namespace $secretName)}}
{{- if not $secret}}
{{- $defUsername:= (b64enc "test")}}
{{- $defPassword:= (b64enc "test")}}
apiVersion: v1
kind: Secret
metadata:
name: "{{$secretName}}"
namespace: "{{.Release.Namespace}}"
type: Opaque
data:
username: {{$defUsername}}
password: {{$defPassword}}
{{- end}}