Kustomize: Feature request: vars from ConfigMap

[yujunz]

Is it possible to create a LIST (not one by one) of variables from ConfigMap just like envFrom ?

Suppose I need to create a bunch of variables for external resources, like security group, domain name and etc. It seems the only way to do it is save them in ConfigMap and refer in variables.

For example:

configMapGenerator:
- name: public
  literals:
  - service-lbs-sg=sg-02f69a511136cb772
  - domain-name=example.com
  - data-store=s3-bucket-name

vars:
- name: SERVICE_LBS_SG
  objref:
    apiVersion: v1
    kind: ConfigMap
    name: public
  fieldref:
    fieldpath: data.service-lbs-sg
- name: DOMAIN_NAME
  objref:
    apiVersion: v1
    kind: ConfigMap
    name: public
  fieldref:
    fieldpath: data.domain-name
- name: DATA_STORE
  objref:
    apiVersion: v1
    kind: ConfigMap
    name: public
  fieldref:
    fieldpath: data.data-store

Ideally, we should be able to generate the variables with

varsFrom:
- configMapRef:
    name: public

If we have already an equivalent solution for this use case, please shed some light on it.

[Liujingfang1]

@yujunz Using vars for ConfigMap data should work.

[yujunz]

Yes, it works if I refer the data one by one. But it is not a joy to create one variable for each, whereas envFrom allows you create a list of environment variable with one item. How do I do it in Kustomize for vars? Could you give an example?

I am expecting something line

varsFrom:
- configMapRef:
    name: public

[Liujingfang1]

I see what you mean. This feature is asking for an enhancement on vars to have a simple way of declaring multiple vars from the same object.

[yujunz]

I can work on it if no other developer has taken it, @Liujingfang1 . Is there a brief developer guide about how to extend kustomize?

[yujunz]

It seems the build steps can be represented in pseudo code below

(o *Options).RunBuild(...)
    kt.MakeCustomizedResMap()

(kt *KustTarget).MakeCustomizeResMap (resmap.ResMap)
    ra := kt.AccuumulateTarget()
    ra.Transform(kt.tFactory.MakeHashTransformer())
    ra.FixBackReferences
    ra.ResolveVars
    return ra.ResMap()

We may need to insert an extra step to expand varsFrom to vars. Not sure where is the right insert point. Could you please shed some light on it, @Liujingfang1 @monopole ?

[Liujingfang1]

I don't think it's necessary to extend current vars to support defining all of the ConfigMap’s data as variables.
Since the variables used in Kustomize are meant primarily to be injected to containers, as env or command arguments.
If you need to inject all of ConfigMap's data into containers, you can use envFrom and use environment variables correspondingly.
What is your usage other than that?

[yujunz]

envFrom can not be used in annotations and other customized fields, as far as I know. I have a live example using a lot of external configurations.

# TODO(yujunz): use `varsFrom` when https://github.com/kubernetes-sigs/kustomize/issues/850 is implemented
- name: vars
  literals:
  - SERVICE_LBS_SG=sg-02f69a34243423
  - ETL_HOSTNAME=etl-controller.example.com
  - ETL_ENVIRONMENT=prod
  - ETL_CONTROLLER_IAM_ROLE=etl.prod.example.com
  - ETL_CONTROLLER_TLS=domain-tls
  - ETL_DATA_STORE=s3://etl-data-store-prod-example-com
  - ETL_AGENT_DOCKERCONFIG=awsecr-cred
  - INGEST_ETL_AGENT_IAM_ROLE=ingest.prod.example.com
  - ETL_ACM_CERT=arn:aws:acm:us-west-1:83423943289:certificate/...
  - APP_IAM_ROLE=app.prod.example.com
  - WORKER_IAM_ROLE=worker.prod.example.com

These variables are to be filled to mostly annotations and also some other fields, e.g.

varReference:
- kind: Deployment
  path: spec/template/spec/volumes/secret/secretName
- kind: Deployment
  path: spec/template/spec/volumes/awsElasticBlockStore/volumeID
- kind: Deployment
  path: spec/template/spec/nodeSelector/failure-domain.beta.kubernetes.io\/zone
- kind: Service
  path: metadata/annotations/service.beta.kubernetes.io\/aws-load-balancer-ssl-cert
- kind: Service
  path: metadata/annotations/service.beta.kubernetes.io\/aws-load-balancer-extra-security-group
- kind: Service
  path: metadata/annotations/external-dns.alpha.kubernetes.io\/hostname

As far as I know, env is limited to command and args. So it seems variable is the only way.

I'm open for better solution though. @Liujingfang1

[yujunz]

It seems I can do it with jsonPatch6902 as mentioned in #318

[jbrette]

@yujunz Just realized that this PR was fixing you problem. Have a look here.
This leverage the configmapgenerator env file, the common annotations ...and the autovariable