Support for nested template in Datasource

[HenryXie1]

We are using vault as datasource on gomplate
The secret path we would like to fetch from config yaml file.
There is nested template case here

It is working with hardcode

{{ (ds "vault:" "versioned/data/testdata").data.client_id }}

config yaml is

spec:
   vault:
     secretPrefix: versioned/data/testdata

Not sure how we can contruct secretPrefix from ds, below is not working
{{ (ds "vault:" {{ (ds "config").spec.vault.secretPrefix }}).data.client_id }}

wonder if it is supported or any workaround? Thanks heaps

[HenryXie1]

Add a variable but it does not work either
{{ $prefix := "{{ (ds \"config\").spec.vault.secretPrefix }}" }} {{ (ds "vault:" $prefix).data.client_id }}

[hairyhenderson]

Hi @HenryXie1, thanks for filing this - I've converted this to a discussion as this is more of a usage question than an issue. If there is indeed a bug or feature request that comes out of this, we can open an issue from it later!

That said, the syntax {{ (ds "vault:" {{ (ds "config").spec.vault.secretPrefix }}).data.client_id }} obviously doesn't work - this is because everything between the outer {{}} is in a template context already, and inner {{}} won't change that.

You can just reference the ds function instead:

{{ (ds "vault:" (ds "config").spec.vault.secretPrefix).data.client_id }}

Or, with a variable (which may be more readable anyway):

{{ $prefix := (ds "config").spec.vault.secretPrefix }}
{{ (ds "vault:" $prefix).data.client_id }}

To make things slightly more readable, and assuming the config datasource is static (unlike the dynamic inline vault datasource you're creating), you can use the context instead:

{{ $prefix := .config.spec.vault.secretPrefix }}
{{ (ds "vault:" $prefix).data.client_id }}

you'd call gomplate with -c to read the config datasource into the context:

$ gomplate -c config=path/to/config.yaml -f mytemplate.tmpl

(see the docs for more details)

Hope this helps - please mark this as answered if it solves your issue.