In a helm template how can i use items in 1 list to iterate over another list

Question

i want to pre-populate a kubernetes cluster with namespaces and their respective secrets for our apps and services. For that i would like to be able to specify 2 lists, 1 list with secrets, and 1 list with namespaces. Each namespace in the list has a list of secrets. Like this values.yaml:

secrets:
  - name: secret1
    data: key1
  - name: secret2
    data: key2
  - name: secret3
    data: key3

namespaces:
  - name: app1
    secrets:
      - secret1
      - secret2
  - name: app2
    secrets:
      - secret1
      - secret3

Then i want to loop over namespaces to create the namespaces, like:

{{- range $namespaces := .Values.namespaces }}
apiVersion: v1
kind: Namespace
metadata:
  name: {{ $namespaces.name }}
---
{{- end }}

In that loop i want another loop inside this loop that creates the secrets per namespace with the data from the secrets list. A bit like this:

{{- range $secrets := .secrets }}
apiVersion: v1
kind: Secret
metadata:
  name: {{ .name }}
  namespace: {{ $namespaces.name }}
type: kubernetes.io/tls
data: $secrets.data
---
{{- end }}

But if i put that loop inside the namespace loop, it just creates all secrets in the secrets list in all namespaces. How can i make the loop only create the secrets specified in the namespaces list?
I think it can be done with the go template index function, but i don't know how.

Solution

I have made reproduction on your problem and find answer for that.

Your example

I used your yamls to create namespaces and changed the second one so it's actually work now.

values.yaml

secrets:
  - name: secret1
    data: key1
  - name: secret2
    data: key2
  - name: secret3
    data: key3

namespaces:
  - name: app1
    secrets:
      - secret1
      - secret2
  - name: app2
    secrets:
      - secret1
      - secret3

templates/namespaces.yaml

{{- range $namespaces := .Values.namespaces }}
apiVersion: v1
kind: Namespace
metadata:
  name: {{ $namespaces.name }}
---
{{- end }}

{{- range $namespace := .Values.namespaces }}                                                                               
{{- range $secret := $namespace.secrets }}                                                                                  
---                                                                                                                         
apiVersion: v1                                                                                                              
kind: Secret                                                                                                                
metadata:                                                                                                                   
  name: {{ $secret }}                                                                                                       
  namespace: {{ $namespace.name }}                                                                                          
type: kubernetes.io/tls                                                                                                     
data: $secrets.data                                                                                                         
---                                                                                                                         
{{- end }}                                                                                                                  
{{- end }}

Result:

COMPUTED VALUES:
namespaces:
- name: app1
  secrets:
  - secret1
  - secret2
- name: app2
  secrets:
  - secret1
  - secret3
secrets:
- data: key1
  name: secret1
- data: key2
  name: secret2
- data: key3
  name: secret3

HOOKS:
MANIFEST:

---
# Source: mychart/templates/namespaces.yaml
apiVersion: v1
kind: Namespace
metadata:
  name: app1
---
# Source: mychart/templates/namespaces.yaml
apiVersion: v1
kind: Namespace
metadata:
  name: app2
---
# Source: mychart/templates/namespaces.yaml
apiVersion: v1
kind: Secret
metadata:
  name: secret1
  namespace: app1                  
type: kubernetes.io/tls
data: $secrets.data
---
# Source: mychart/templates/namespaces.yaml
apiVersion: v1
kind: Secret
metadata:
  name: secret2
  namespace: app1                  
type: kubernetes.io/tls
data: $secrets.data
---
# Source: mychart/templates/namespaces.yaml
apiVersion: v1
kind: Secret
metadata:
  name: secret1
  namespace: app2                  
type: kubernetes.io/tls
data: $secrets.data
---
# Source: mychart/templates/namespaces.yaml
apiVersion: v1
kind: Secret
metadata:
  name: secret3
  namespace: app2                  
type: kubernetes.io/tls
data: $secrets.data

My idea of doing that

Instead of creating secrets for namespaces, do it the other way around, create secrets and add namespaces to them.

values.yaml

Secret1:
- namespace1
- namespace2

Secret2:
- namespace2

templates/namespaces.yaml

{{- range $namespaces := .Values.namespaces }}
apiVersion: v1
kind: Namespace
metadata:
  name: {{ $namespaces.name }}
---
{{- end }}

templates/secrets.yaml

{{- range .Values.Secret1 }}
---
apiVersion: v1
data:
  password: MWYyZDFlMmU2N2Rm
  username: YWRtaW4=
kind: Secret
metadata:
  creationTimestamp: null
  name: secret1
  namespace: {{ . }}
{{- end}}
{{- range .Values.Secret2 }}
---
apiVersion: v1
data:
  password: MWYyZDFlMmU2N2Rm
  username: YWRtaW4=
kind: Secret
metadata:
  creationTimestamp: null
  name: secret2
  namespace: {{ . }}
{{- end}}

Result:

COMPUTED VALUES:
Secret1:
- namespace1
- namespace2
Secret2:
- namespace2
namespaces:
- name: namespace1
- name: namespace2

HOOKS:
MANIFEST:

---
# Source: mychart/templates/namespaces2.yaml
apiVersion: v1
kind: Namespace
metadata:
  name: namespace1
---
# Source: mychart/templates/namespaces2.yaml
apiVersion: v1
kind: Namespace
metadata:
  name: namespace2
---
# Source: mychart/templates/namespaces.yaml
apiVersion: v1                                                                                                              
data:                                                                                                                       
  password: UyFCXCpkJHpEc2I=                                                                                                   
  username: ZGV2dXNlcg==                                                                                                      
kind: Secret                                                                                                                
metadata:                                                                                                                   
  creationTimestamp: null                                                                                                   
  name: secret1                                                                                                             
  namespace: namespace2
---
# Source: mychart/templates/namespaces.yaml
apiVersion: v1                                                                                                              
data:                                                                                                                       
  password: ZGV2dXNlcg==                                                                                              
  username: UyFCXCpkJHpEc2I=                                                                                                    
kind: Secret                                                                                                                
metadata:                                                                                                                   
  creationTimestamp: null                                                                                                   
  name: secret2                                                                                                             
  namespace: namespace2
---
# Source: mychart/templates/namespaces.yaml
apiVersion: v1                                                                                                              
data:                                                                                                                       
  password: UyFCXCpkJHpEc2I=                                                                                                   
  username: ZGV2dXNlcg==                                                                                                      
kind: Secret                                                                                                                
metadata:                                                                                                                   
  creationTimestamp: null                                                                                                   
  name: secret1                                                                                                             
  namespace: namespace1

More informations about Flow Control(if,else if,range) can be found here.