Helm | - 0 views
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Templates generate manifest files, which are YAML-formatted resource descriptions that Kubernetes can understand.
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service.yaml: A basic manifest for creating a service endpoint for your deployment
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In Kubernetes, a ConfigMap is simply a container for storing configuration data.
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deployment.yaml: A basic manifest for creating a Kubernetes deployment
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using the suffix .yaml for YAML files and .tpl for helpers.
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It is just fine to put a plain YAML file like this in the templates/ directory.
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helm get manifest
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The helm get manifest command takes a release name (full-coral) and prints out all of the Kubernetes resources that were uploaded to the server. Each file begins with --- to indicate the start of a YAML document
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Names should be unique to a release
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The name: field is limited to 63 characters because of limitations to the DNS system.
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release names are limited to 53 characters
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{{ .Release.Name }}
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A template directive is enclosed in {{ and }} blocks.
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The values that are passed into a template can be thought of as namespaced objects, where a dot (.) separates each namespaced element.
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The leading dot before Release indicates that we start with the top-most namespace for this scope
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The Release object is one of the built-in objects for Helm
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When you want to test the template rendering, but not actually install anything, you can use helm install ./mychart --debug --dry-run
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Using --dry-run will make it easier to test your code, but it won’t ensure that Kubernetes itself will accept the templates you generate.
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Objects are passed into a template from the template engine.
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create new objects within your templates
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Objects can be simple, and have just one value. Or they can contain other objects or functions.
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Release is one of the top-level objects that you can access in your templates.
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Release.Namespace: The namespace to be released into (if the manifest doesn’t override)
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Values: Values passed into the template from the values.yaml file and from user-supplied files. By default, Values is empty.
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Chart: The contents of the Chart.yaml file.
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Files: This provides access to all non-special files in a chart.
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Files.Get is a function for getting a file by name
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Files.GetBytes is a function for getting the contents of a file as an array of bytes instead of as a string. This is useful for things like images.
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Template: Contains information about the current template that is being executed
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BasePath: The namespaced path to the templates directory of the current chart
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The built-in values always begin with a capital letter.
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Go’s naming convention
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use only initial lower case letters in order to distinguish local names from those built-in.
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If this is a subchart, the values.yaml file of a parent chart
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Individual parameters passed with --set
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values.yaml is the default, which can be overridden by a parent chart’s values.yaml, which can in turn be overridden by a user-supplied values file, which can in turn be overridden by --set parameters.
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While structuring data this way is possible, the recommendation is that you keep your values trees shallow, favoring flatness.
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If you need to delete a key from the default values, you may override the value of the key to be null, in which case Helm will remove the key from the overridden values merge.
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Kubernetes would then fail because you can not declare more than one livenessProbe handler.
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When injecting strings from the .Values object into the template, we ought to quote these strings.
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quote
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Template functions follow the syntax functionName arg1 arg2...
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While we talk about the “Helm template language” as if it is Helm-specific, it is actually a combination of the Go template language, some extra functions, and a variety of wrappers to expose certain objects to the templates.
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Drawing on a concept from UNIX, pipelines are a tool for chaining together a series of template commands to compactly express a series of transformations.
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pipelines are an efficient way of getting several things done in sequence
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The repeat function will echo the given string the given number of times
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default DEFAULT_VALUE GIVEN_VALUE. This function allows you to specify a default value inside of the template, in case the value is omitted.
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all static default values should live in the values.yaml, and should not be repeated using the default command
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Operators are implemented as functions that return a boolean value.
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To use eq, ne, lt, gt, and, or, not etcetera place the operator at the front of the statement followed by its parameters just as you would a function.
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if and
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if or
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with to specify a scope
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range, which provides a “for each”-style loop
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block declares a special kind of fillable template area
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A pipeline is evaluated as false if the value is: a boolean false a numeric zero an empty string a nil (empty or null) an empty collection (map, slice, tuple, dict, array)
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incorrect YAML because of the whitespacing
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When the template engine runs, it removes the contents inside of {{ and }}, but it leaves the remaining whitespace exactly as is.
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{{- (with the dash and space added) indicates that whitespace should be chomped left, while -}} means whitespace to the right should be consumed.
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Newlines are whitespace!
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an * at the end of the line indicates a newline character that would be removed
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Be careful with the chomping modifiers.
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the indent function
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Scopes can be changed. with can allow you to set the current scope (.) to a particular object.
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Inside of the restricted scope, you will not be able to access the other objects from the parent scope.
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range
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The range function will “range over” (iterate through) the pizzaToppings list.
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Just like with sets the scope of ., so does a range operator.
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The toppings: |- line is declaring a multi-line string.
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not a YAML list. It’s a big string.
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the data in ConfigMaps data is composed of key/value pairs, where both the key and the value are simple strings.
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The |- marker in YAML takes a multi-line string.
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range can be used to iterate over collections that have a key and a value (like a map or dict).
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In Helm templates, a variable is a named reference to another object. It follows the form $name
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Variables are assigned with a special assignment operator: :=
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{{- $relname := .Release.Name -}}
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capture both the index and the value
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the integer index (starting from zero) to $index and the value to $topping
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For data structures that have both a key and a value, we can use range to get both
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Variables are normally not “global”. They are scoped to the block in which they are declared.
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one variable that is always global - $ - this variable will always point to the root context.
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$.
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$.
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Helm template language is its ability to declare multiple templates and use them together.
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A named template (sometimes called a partial or a subtemplate) is simply a template defined inside of a file, and given a name.
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when naming templates: template names are global.
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If you declare two templates with the same name, whichever one is loaded last will be the one used.
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you should be careful to name your templates with chart-specific names.
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templates in subcharts are compiled together with top-level templates
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naming convention is to prefix each defined template with the name of the chart: {{ define "mychart.labels" }}
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Helm has over 60 available functions.
