Do not use SubPath for mounting ConfigMap and Secret configuration files if Key not specified

[gazarenkov]

Problems:

• For the time we extensively use mounting CM/Secret configuration files using SubPath to not to cause overwriting the whole directory. The problem of this approach is that mounted configuration file is not changed when respective CM/Secret data changed (see: Investigate updating app-config' ConfigMap and extra files' ConfigMap and Secret #125 ).

Proposals:

• Not to use SubPath for mounting CM/Secret if Key is not pointed and mount Data files to dedicated directory, taking from CM/Secret name or (better UX but requires slightly API change) add another field or move mountPath: to the configuration spec, per CM/Secret

Example:

Incompatible with current:

spec:
  application:
    extraFiles:
      configMaps:
        - name: 
           mountPath: /tmp/my-extra-files

Compatible with current:

spec:
  application:
      extraFiles:
      mountPath: /tmp
      configMaps:
        - name: 
          directory:  my-extra-files

In both cases Operator should generate MountVolume with MountPath = /tmp/my-extra-files, w/o SubPath

[gazarenkov]

Related to #125

[gazarenkov]

After discussion and some reconsideration, taking into account:

• even if mounted data will be refreshed with changing ConfigMap it will not help in all the cases since Backstage application does not refreshes the data in all the cases so container reconciliation is needed in general case anyway (@kadel 's point)
• using generated name for volume directory will require the knowledge of how this name is formed for some cases (e g extra files), which is not convenient
• we need marshalling app-config's CM data anyway to be able to form --config args

I changed my opinion regarding applicability of proposed issue for current API and its importance
I still believe that volume data refresh is a feature we should exploit as much as possible but not with (potentially generated) CM name.
I believe, to make it usable, we need to introduce per-CM and per-Secret mountPath first.

[kadel]

I believe, to make it usable, we need to introduce per-CM and per-Secret mountPath first.

How would this look in Backstage CR definition?

[gazarenkov]

Not actual with recreating Pod after modify CMs/Secrets. #236