@pmcgrath

Checkout here.

it seems I understand your issue. I have the same question before, but there is an answer actually in your situation.

To brief your case, you have a configmap(settings.json: blahblah), and want to mount into a folder /app. Then below is what you need to know:

1. Once you mount a volume(no matter it is configmap or others), it overrides the mountPath, so in your case, the /app folder will only contain settings.json.
2. I know it is not what you expected, so you have to specify the mountPath: /app/settings.json, only that way, the original content in /app folders won't be affected.
3. well, when you do the second step, you remember that configmap is actually a list of key-value pairs, you only need one of the keys(though you actually have only one as well), so you need to tell the volume mounts to use a subpath from you configmap.

This is something that you will get eventually:

containers:
- volumeMounts:
  - name: demo-config
    mountPath: /app/settings.json
    subPath: settings.json
volumes:
- name: demo-config
  configMap:
    name: demo

@zhouhaibing089
Thanks for the reply, works based on your suggestion, I appreciate the explanation

I am happy to close this issue
Pat

For reference, the original mention of this solution seems to be here: #23748 (comment)

It looks like the documentation for this is missing, which makes this case fairly confusing/misleading, and the projection docs seem to make it more misleading as well -- not sure if it's missing because auto updates apparently don't work as per that issue

The requirement for the file name to be specified both under mountPath and subPath is counterintuitive.

The solution provided by @zhouhaibing089 works but the content of the mounted file at subPath doesn't update if we edit it in the resembled ConfigMap.

IMO, this isn't really solved. There should be an option to append each key rather than overwrite.

Something like:

kind: ConfigMap
apiVersion: v1
metadata:
  name: nginx-conf
data:
  example1.conf: |
    server {
      server_name example1.com;
      # config here...
    }
  example2.conf: |
    server {
      server_name example2.com;
      # config here...
    }

So that...

- name: nginx-conf
  mountPath: /etc/nginx/conf.d
  append: true

... keeps the existing default.conf and any other artefacts of the Docker image, but augments with example*.conf

Repeating the same info in subPath is just icky.

+1 on @leebenson 's append: true option.

According to @leebenson answer: can anyone explain where from is coming append: true option ??

it does not work for me, i got:

error: error validating "hdfs/21-namenode-statefulset.yaml": error validating data: ValidationError(StatefulSet.spec.template.spec.containers[1].volumeMounts[1]): unknown field "append" in io.k8s.api.core.v1.VolumeMount; if you choose to ignore these errors, turn validation off with --validate=false

Also, it is not present in api docs for volume mount :
https://k8smeetup.github.io/docs/api-reference/v1.9/#volumemount-v1-core

According to @leebenson answer: can anyone explain where from is coming append: true option ??

it does not work for me, i got:

error: error validating "hdfs/21-namenode-statefulset.yaml": error validating data: ValidationError(StatefulSet.spec.template.spec.containers[1].volumeMounts[1]): unknown field "append" in io.k8s.api.core.v1.VolumeMount; if you choose to ignore these errors, turn validation off with --validate=false

Also, it is not present in api docs for volume mount :
https://k8smeetup.github.io/docs/api-reference/v1.9/#volumemount-v1-core

it doesn't exist, it's a suggestion. a good one for the use case.

I tried to use this method, but I got a Read-only file system error, when I applied the statefulset. Does anyone know how to fix that?
(I'm overwriting an existing file, that contains settings for elasticsearch, actual error message --> /usr/share/elasticsearch/bin/run.sh: line 28: ./config/elasticsearch.yml: Read-only file system)