github.com/y-taka-23/helm@v2.8.0+incompatible/docs/chart_best_practices/templates.md (about)

     1  # Templates
     2  
     3  This part of the Best Practices Guide focuses on templates.
     4  
     5  ## Structure of templates/
     6  
     7  The templates directory should be structured as follows:
     8  
     9  - Template files should have the extension `.yaml` if they produce YAML output. The
    10    extension `.tpl` may be used for template files that produce no formatted content.
    11  - Template file names should use dashed notation (`my-example-configmap.yaml`), not camelcase.
    12  - Each resource definition should be in its own template file.
    13  - Template file names should reflect the resource kind in the name. e.g. `foo-pod.yaml`,
    14    `bar-svc.yaml`
    15  
    16  ## Names of Defined Templates
    17  
    18  Defined templates (templates created inside a `{{ define }} ` directive) are
    19  globally accessible. That means that a chart and all of its subcharts will have
    20  access to all of the templates created with `{{ define }}`.
    21  
    22  For that reason, _all defined template names should be namespaced._
    23  
    24  Correct:
    25  
    26  ```yaml
    27  {{- define "nginx.fullname" }}
    28  {{/* ... */}}
    29  {{ end -}}
    30  ```
    31  
    32  Incorrect:
    33  
    34  ```yaml
    35  {{- define "fullname" -}}
    36  {{/* ... */}}
    37  {{ end -}}
    38  ```
    39  It is highly recommended that new charts are created via `helm create` command as the template names are automatically defined as per this best practice.
    40  
    41  ## Formatting Templates
    42  
    43  Templates should be indented using _two spaces_ (never tabs).
    44  
    45  Template directives should have whitespace after the opening  braces and before the
    46  closing braces:
    47  
    48  Correct:
    49  ```
    50  {{ .foo }}
    51  {{ print "foo" }}
    52  {{- print "bar" -}}
    53  ```
    54  
    55  Incorrect:
    56  ```
    57  {{.foo}}
    58  {{print "foo"}}
    59  {{-print "bar"-}}
    60  ```
    61  
    62  Templates should chomp whitespace where possible:
    63  
    64  ```
    65  foo:
    66    {{- range .Values.items }}
    67    {{ . }}
    68    {{ end -}}
    69  ```
    70  
    71  Blocks (such as control structures) may be indented to indicate flow of the template code.
    72  
    73  ```
    74  {{ if $foo -}}
    75    {{- with .Bar }}Hello{{ end -}}
    76  {{- end -}} 
    77  ```
    78  
    79  However, since YAML is a whitespace-oriented language, it is often not possible for code indentation to follow that convention.
    80  
    81  ## Whitespace in Generated Templates
    82  
    83  It is preferable to keep the amount of whitespace in generated templates to
    84  a minimum. In particular, numerous blank lines should not appear adjacent to each
    85  other. But occasional empty lines (particularly between logical sections) is
    86  fine.
    87  
    88  This is best:
    89  
    90  ```yaml
    91  apiVersion: batch/v1
    92  kind: Job
    93  metadata:
    94    name: example
    95    labels:
    96      first: first
    97      second: second
    98  ```
    99  
   100  This is okay:
   101  
   102  ```yaml
   103  apiVersion: batch/v1
   104  kind: Job
   105  
   106  metadata:
   107    name: example
   108  
   109    labels:
   110      first: first
   111      second: second
   112  
   113  ```
   114  
   115  But this should be avoided:
   116  
   117  ```yaml
   118  apiVersion: batch/v1
   119  kind: Job
   120  
   121  metadata:
   122    name: example
   123  
   124  
   125  
   126  
   127  
   128    labels:
   129      first: first
   130  
   131      second: second
   132  
   133  ```
   134  
   135  ## Comments (YAML Comments vs. Template Comments)
   136  
   137  Both YAML and Helm Templates have comment markers.
   138  
   139  YAML comments:
   140  ```yaml
   141  # This is a comment
   142  type: sprocket
   143  ```
   144  
   145  Template Comments:
   146  ```yaml
   147  {{- /*
   148  This is a comment.
   149  */ -}}
   150  type: frobnitz
   151  ```
   152  
   153  Template comments should be used when documenting features of a template, such as explaining a defined template:
   154  
   155  ```yaml
   156  {{- /*
   157  mychart.shortname provides a 6 char truncated version of the release name.
   158  */ }}
   159  {{ define "mychart.shortname" -}}
   160  {{ .Release.Name | trunc 6 }}
   161  {{- end -}}
   162  
   163  ```
   164  
   165  Inside of templates, YAML comments may be used when it is useful for Helm users to (possibly) see the comments during debugging.
   166  
   167  ```
   168  # This may cause problems if the value is more than 100Gi
   169  memory: {{ .Values.maxMem | quote }}
   170  ```
   171  
   172  The comment above is visible when the user runs `helm install --debug`, while
   173  comments specified in `{{- /* */ -}}` sections are not.
   174  
   175  ## Use of JSON in Templates and Template Output
   176  
   177  YAML is a superset of JSON. In some cases, using a JSON syntax can be more
   178  readable than other YAML representations.
   179  
   180  For example, this YAML is closer to the normal YAML method of expressing lists:
   181  
   182  ```yaml
   183  arguments: 
   184    - "--dirname"
   185    - "/foo"
   186  ```
   187  
   188  But it is easier to read when collapsed into a JSON list style:
   189  
   190  ```yaml
   191  arguments: ["--dirname", "/foo"]
   192  ```
   193  
   194  Using JSON for increased legibility is good. However, JSON syntax should not
   195  be used for representing more complex constructs.
   196  
   197  When dealing with pure JSON embedded inside of YAML (such as init container
   198  configuration), it is of course appropriate to use the JSON format.