Accessing Files Inside Templates

    Helm provides access to files through the object. Before we get going with the template examples, though, there are a few things to note about how this works:

    • It is okay to add extra files to your Helm chart. These files will be bundled and sent to Tiller. Be careful, though. Charts must be smaller than 1M because of the storage limitations of Kubernetes objects.
    • Some files cannot be accessed through the .Files object, usually for security reasons.
      • Files in templates/ cannot be accessed.
      • Files excluded using .helmignore cannot be accessed.

    • Charts do not preserve UNIX mode information, so file-level permissions will have no impact on the availability of a file when it comes to the .Files object.

    • Basic example

    • Glob patterns
    • Encoding

    With those caveats behind, let’s write a template that reads three files into our ConfigMap. To get started, we will add three files to the chart, putting all three directly inside of the mychart/ directory.

    config1.toml:

    config2.toml:

    1. message = This is config 2

    config3.toml:

    1. message = Goodbye from config 3

    Each of these is a simple TOML file (think old-school Windows INI files). We know the names of these files, so we can use a range function to loop through them and inject their contents into our ConfigMap.

    1. apiVersion: v1
    2. kind: ConfigMap
    3.   name: {{ .Release.Name }}-configmap
    4. data:
    5.   {{- $files := .Files }}
    6.   {{- range tuple "config1.toml" "config2.toml" "config3.toml" }}
    7.   {{ . }}: |-
    8.     {{ $files.Get . }}
    9.   {{- end }}

    Running this template will produce a single ConfigMap with the contents of all three files:

    Path helpers

    When working with files, it can be very useful to perform some standard operations on the file paths themselves. To help with this, Helm imports many of the functions from Go’s package for your use. They are all accessible with the same names as in the Go package, but with a lowercase first letter. For example, Base becomes base, etc.

    The imported functions are:

    • Base
    • Dir
    • Ext
    • IsAbs
    • Clean

    As your chart grows, you may find you have a greater need to organize your files more, and so we provide a Files.Glob(pattern string) method to assist in extracting certain files with all the flexibility of glob patterns.

    .Glob returns a Files type, so you may call any of the Files methods on the returned object.

    For example, imagine the directory structure:

    1. foo/:
    2.   foo.txt foo.yaml
    4. bar/:
    5.   bar.go bar.conf baz.yaml

    You have multiple options with Globs:

    1. {{ $root := . }}
    2. {{ range $path, $bytes := .Files.Glob "**.yaml" }}
    3. {{ $path }}: |-
    4. {{ $root.Files.Get $path }}

    Or

    1. {{ range $path, $bytes := .Files.Glob "foo/*" }}
    2. {{ base $path }}: '{{ $root.Files.Get $path | b64enc }}'
    3. {{ end }}

    ConfigMap and Secrets utility functions

    It is very common to want to place file content into both configmaps and secrets, for mounting into your pods at run time. To help with this, we provide a couple utility methods on the Files type.

    For further organization, it is especially useful to use these methods in conjunction with the Glob method.

    Given the directory structure from the Glob example above:

    You can import a file and have the template base-64 encode it to ensure successful transmission:

    2. kind: Secret
    3. metadata:
    4.   name: {{ .Release.Name }}-secret
    5. type: Opaque
    6. data:
    7.   token: |-
    8.     {{ .Files.Get "config1.toml" | b64enc }}

    The above will take the same config1.toml file we used before and encode it:

    1. # Source: mychart/templates/secret.yaml
    2. apiVersion: v1
    3. kind: Secret
    4. metadata:
    5.   name: lucky-turkey-secret
    6. type: Opaque
    7. data:
    8.   token: |-
    9.     bWVzc2FnZSA9IEhlbGxvIGZyb20gY29uZmlnIDEK

    Lines

    Sometimes it is desirable to access each line of a file in your template. We provide a convenient Lines method for this.

    1. data:
    2.     {{ . }}{{ end }}

    Currently, there is no way to pass files external to the chart during helm install. So if you are asking users to supply data, it must be loaded using helm install -f or .

    This discussion wraps up our dive into the tools and techniques for writing Helm templates. In the next section we will see how you can use one special file, templates/NOTES.txt, to send post-installation instructions to the users of your chart.