Go Template¶
Template¶
The template feature allows administrators to dynamically generate values from information in Paas and/or PaasConfig. This provides flexibility for other organisations using the Paas operator with other business logic.
Syntax¶
Template options support standard Go Template syntax, allowing all values from the Paas and PaasConfig to be referenced. See more examples below. In addition to the default Go Template functions, we've added support for all Sprout Go Template functions.
Behavior of multivalued and single valued results¶
Depending on the result of the Go Template, one of three things can happen:
- if the result can be parsed as a list:
- The key of the resulting item (label or custom field) is derived from the name of the template, suffixed with an underscore and an integer (number in the list of this item).
- The value of the resulting item is the direct value of the item in the list
- if the result can be parsed as map:
- The key of the resulting item (label or custom field) is derived from the name of the template, suffixed with an underscore and the key of the map item
- The value of the resulting item is the direct value of the map item
- If the result is not parsable as list or map:
- The key of the resulting item (label or custom field) is derived from the name of the template
- The value of the resulting item is derived from the exact returned string
Note
If you need to return a map or list as a single string value in a field, you have the following options: - convert the map to a string representation using toYaml or toJson, and add quoting to make sure it is parsed as one string - create a map with one key/value pair and set the resulting string as the value
Developing Go Templates¶
For easier validation and debugging of templates, we recommend using Repeat It, an online tool to test and validate your Go Templates.
Implementations¶
Labels with go templating¶
Administrators can define labels to be added to resources managed by a Paas. The implementation is based on Go Templating, and has the Paas and Resource as inputs. This feature can be used to: - copy labels (or annotations) from the Paas, (or PaasConfig) to labels on the specific resource - use specific fields in the Paas (or PaasConfig) to define extra labels
!!!! Note This feature replaces certain hardcoded implementations that were previously implemented. If you want to keep the behavior, please add the following to your PaasConfig:
```yml
apiVersion: cpet.belastingdienst.nl/v1alpha2
kind: PaasConfig
metadata:
name: opr-paas-config
spec:
...
templating:
clusterQuotaLabels:
"": '{{ range $key, $value := .Paas.Labels }}{{ if ne $key "app.kubernetes.io/instance" }}{{$key}}: {{$value}}\n{{end}}{{end}}'
groupLabels:
"": '{{ range $key, $value := .Paas.Labels }}{{ if ne $key "app.kubernetes.io/instance" }}{{$key}}: {{$value}}\n{{end}}{{end}}'
namespaceLabels:
"": '{{ range $key, $value := .Paas.Labels }}{{ if ne $key "app.kubernetes.io/instance" }}{{$key}}: {{$value}}\n{{end}}{{end}}'
"argocd.argoproj.io/managed-by": "{{ .Paas.Spec.ManagedByPaas }}-argocd"
roleBindingLabels:
"": '{{ range $key, $value := .Paas.Labels }}{{ if ne $key "app.kubernetes.io/instance" }}{{$key}}: {{$value}}\n{{end}}{{end}}'
```
Capability fields with Go Template¶
Custom fields per capability¶
The Paas operator allows administrator to define custom fields which can be set by requestors and end up as fields in the list generator in the ApplicationSet that defines the Application for the capability for the Paas.
For more info, see api-guide on capability custom field configuration in the Paas
Custom fields for all capabilities¶
In addition to setting custom fields for specific capabilities, the Paas operator also allows administrators to define custom fields that apply to all capabilities. There are two main differences: 1. These custom fields cannot be overruled by a custom field for a specific Paas 2. These custom fields are generically applied to all capabilities.
!!!! Note This feature replaces certain hardcoded implementations that were previously implemented. If you want to keep the behavior, please add the following to your PaasConfig:
```yml
apiVersion: cpet.belastingdienst.nl/v1alpha2
kind: PaasConfig
metadata:
name: opr-paas-config
spec:
...
templating:
genericCapabilityFields:
requestor: "{{ .Paas.Spec.Requestor }}",
service: "{{ (splitn \"-\" 2 .Paas.Name)._0 }}",
subservice: "{{ (splitn \"-\" 2 .Paas.Name)._1 }}",
```
Examples¶
This chapter shows some examples of Go Templates that are used in this project and explains how they work and why they are phrased as such.
RBAC block¶
The following example loops through the groups in the paas spec and generates a RBAC line for every group
Example
Reference PaasConfig values¶
You can reference values from the PaasConfig as well by referencing .Config:
Return multiple keys as a map¶
Your template could return a map (using key: value formatting) to return multiple key/value pairs
This would return two key/value pairs. If name of the template would be set to my_map, values would have keys my_map_debug and my_map_argo.
Return multiple keys as a list¶
Your template could return a list (using - value formatting) to return multiple key/value pairs.
Example
This would return three key/value pairs. If name of the template would be set to my_list, values would have keys my_list_0 and my_list_1.
Adding all labels, except for a specific key¶
Ideally this could be done using the omit dict function, but unfortunately,
the dict is implemented as map[string]any, and labels are implemented as map[string]string and go does not automatically convert.
We have used a range and if statement to create all key/value pairs one by one. Note that the Go Template is spread across multiple lines. This ensures that each key is placed on a separate line, and is thus correctly parsed as an individual key/value pair.