Helm: generate comma separated list - kubernetes

Question

Using Helm templates, I'm trying to generate a list of server names based on a number in values.yaml. The dot for this template is set to the number (its a float64).
{{- define "zkservers" -}}
{{- $zkservers := list -}}
{{- range int . | until -}}
{{- $zkservers := print "zk-" . ".zookeeper" | append $zkservers -}}
{{- end -}}
{{- join "," $zkservers -}}
{{- end -}}
For an input of, say, 3 I'm expecting this to produce:
zk-0.zookeeper,zk-1.zookeeper,zk-2.zookeeper
It produces nothing.
I understand that the line within the range block is a no-op since the variable $zkservers is a new variable each time the loop iterates. It is not the same variable as the $zkservers in the outer scope.
I hope the intention is clear of what I want to do. I am at a loss how to do it.
Anyone know how to do this with Helm templates?

Answer 1

For those from 2020+ it now can be achieved as simple as that:
{{ join "," .Values.some.array }}
It produces the correct output:
value: "test1,test2,test3"
At least it works with (more or less) recent versions of helm-cli:
Client: &version.Version{SemVer:"v2.16.2", GitCommit:"bbdfe5e7803a12bbdf97e94cd847859890cf4050", GitTreeState:"clean"}

Answer 2

Another quick way of doing it:
{{- define "helm-toolkit.utils.joinListWithComma" -}}
{{- $local := dict "first" true -}}
{{- range $k, $v := . -}}{{- if not $local.first -}},{{- end -}}{{- $v -}}{{- $_ := set $local "first" false -}}{{- end -}}
{{- end -}}
If you give this input like:
test:
- foo
- bar
And call with:
{{ include "helm-toolkit.utils.joinListWithComma" .Values.test }}
You'll get the following rendered:
foo,bar
This is from OpenStack-Helm's Helm-toolkit chart, which is a collection of utilities for similar purposes.

Answer 3

I faced with the same problem and your solution with dictionary saved my day. It's a good workaround and it can be just a little simpler:
{{- define "zkservers" -}}
{{- $zk := dict "servers" (list) -}}
{{- range int . | until -}}
{{- $noop := printf "zk-%d.zookeeper" . | append $zk.servers | set $zk "servers" -}}
{{- end -}}
{{- join "," $zk.servers -}}
{{- end -}}

Answer 4

You're currently defining a new varialbe in the scope of the list while you want to alter the existing value.
In order to fix your bug, you only need to change the way you assign the value to $zkservers:
- {{- $zkservers := print "zk-" . ".zookeeper" | append $zkservers -}}
+ {{- $zkservers = print "zk-" . ".zookeeper" | append $zkservers -}}
which gives you the following script:
{{- define "zkservers" -}}
{{- $zkservers := list -}}
{{- range int . | until -}}
{{- $zkservers = print "zk-" . ".zookeeper" | append $zkservers -}}
{{- end -}}
{{- join "," $zkservers -}}
{{- end -}}
With this slight modification, {{ include "zkservers" 3 }}gives you the output zk-0.zookeeper,zk-1.zookeeper,zk-2.zookeeper

Answer 5

I was doing the same but on elasticsearch helm chart. Please find my example
values.yml:
...
replicaCount: 3
...
StatefulSets.yaml:
...
containers:
- name: {{ .Chart.Name }}
image: "{{ .Values.registry_address }}/{{ .Values.image.name }}:{{ .Chart.AppVersion }}"
env:
- name: ELASTICSEARCH_CLUSTER_NAME
value: "{{ .Values.env.ELASTICSEARCH_CLUSTER_NAME }}"
- name: ELASTICSEARCH_DISCOVERY_ZEN_PING_UNICAST_HOSTS
value: "{{ template "nodes" .Values }}"
...
_helpers.tpl:
{{/* vim: set filetype=mustache: */}}
{{- define "nodes" -}}
{{- $nodeCount := .replicaCount | int }}
{{- range $index0 := until $nodeCount -}}
{{- $index1 := $index0 | add1 -}}
elasticsearch-{{ $index0 }}.elasticsearch{{ if ne $index1 $nodeCount }},{{ end }}
{{- end -}}
{{- end -}}
This produces a comma separated list:
...
- name: ELASTICSEARCH_DISCOVERY_ZEN_PING_UNICAST_HOSTS
value: "elasticsearch-0.elasticsearch,elasticsearch-1.elasticsearch,elasticsearch-2.elasticsearch"
...

Answer 6

I got it working using:
{{- define "zkservers" -}}
{{- $dot := dict "nodes" (int .) "servers" (list) -}}
{{- template "genservers" $dot -}}
{{- join "," $dot.servers -}}
{{- end -}}
{{- define "genservers" -}}
{{- range until .nodes -}}
{{- $noop := print "zk-" . ".zookeeper" | append $.servers | set $ "servers" -}}
{{- end -}}
{{- end -}}
Seems a little bit verbose for what should normally be a simple one/two liner :)

Answer 7

How about just rendering and then trimming?
{{- include "template" . | trimSuffix "," -}}