helm templating with toYaml

Question

I have values.yml file that takes in a list of ports with this format and default values:

Ports:
  - number: 443
    protocol: http

The script that output the list of port to use as my input gives me this format:

port_list=$(./get_ports.sh)

output:

- 80
- 8080

I want the resulting rendered template to be

Ports:
  - number: 80
  - number: 8080

How would I accomplish this? I tried the following in my template file:

{{- with .Values.Ports }}
Ports:
  {{- toYaml . | nindent 8 }}
{{- end }}

using helm template and setting values.Ports=$port_list, it ended up giving me a pipe and an extra dash like below, which I do not know where they come from, how do I accomplish getting to the format I want above based on the input?

Ports:
|-
  - number: 80
  - number: 8080

As a bonus, I would also like to have a default protocol in my port list when the protocol isn't specified.

Ports:
  - number: 80
    protocol: http
  - number: 8080
    protocol: http

Is there a clean way to do this with just templating?

Solution

First, you have to know about the YAML syntax about string. You can find it by searching on the internet. For example: see YAML Multiline.

| enables multiline string and - chops the trailing \n from the end of the string.

The reason for appearing |- is the output of the script get_ports.sh (is being treated as a single string). You can test this,

port_list=$(get_ports.sh)
# pass this to the `--set` flag in both of the following ways
# 01: pass the var $port_list
--set ports=$port_list
# 02: directly pass the value of the var $port_list
--set ports="- 80
- 8080"

For both of the tests you have the same output as follows:

ports:
|-
  - 80
  - 8080

If you put a newline at the end of the output of your script, then you will see the - has disappeared.

--set ports="- 80
- 8080
"

The output is like as following:

ports:
|
  - 80
  - 8080

Now try in a different way. Change your template to like this one:

{{- if .Values.ports }}
  {{- print "ports:" | nindent 2 }}
  {{- range $_, $p := .Values.ports }}
    - number: {{ $p }}
      protocol: http
  {{- end }}
{{- end }}

This template expects the value of your ports in the --set flag as a list (not a string). According to my knowledge at the time of writing this answer, to provide a list value in --set flag either of the followings can be used:

• --set ports={80\,8080}
• --set ports[0]=80,ports[1]=8080

Now the output is same as you want.

$ helm template test . --set ports={80\,8080}
ports:
  - number: 80
    protocol: http
  - number: 8080
    protocol: http

So all you need to process the output of get_ports.sh. That's it.

You may need to adjust the indentation in the template

Comments

[Mr. Llama]

I know I'm a bit late here, but I strongly recommend against using toYaml because it means you suddenly have to care about indentation. Given that YAML is a superset of JSON, it's probably better to just use Ports: {{ toJson . }} instead. You will get the desired result without having to worry about whitespace or formatting issues.

[Jimmy Smith]

Excellent answer, thank you. This was exactly what I needed.