차트 개발 팁과 비법
This guide covers some of the tips and tricks Helm chart developers have learned while building production-quality charts.
템플릿 함수 이해하기
Helm uses Go templates for templating your resource files. While Go ships several built-in functions, we have added many others.
First, we added all of the functions in the Sprig library.
We also added two special template functions: include
and required
. The
include
function allows you to bring in another template, and then pass the
results to other template functions.
For example, this template snippet includes a template called mytpl
, then
lowercases the result, then wraps that in double quotes.
value: {{ include "mytpl" . | lower | quote }}
The required
function allows you to declare a particular values entry as
required for template rendering. If the value is empty, the template rendering
will fail with a user submitted error message.
The following example of the required
function declares an entry for
.Values.who is required, and will print an error message when that entry is
missing:
value: {{ required "A valid .Values.who entry required!" .Values.who }}
문자열에는 따옴표를 쓰고, 정수형에는 쓰지 말자
When you are working with string data, you are always safer quoting the strings than leaving them as bare words:
name: {{ .Values.MyName | quote }}
But when working with integers do not quote the values. That can, in many cases, cause parsing errors inside of Kubernetes.
port: {{ .Values.Port }}
This remark does not apply to env variables values which are expected to be string, even if they represent integers:
env:
- name: HOST
value: "http://host"
- name: PORT
value: "1234"
##'include' 함수 사용하기
Go provides a way of including one template in another using a built-in
template
directive. However, the built-in function cannot be used in Go
template pipelines.
To make it possible to include a template, and then perform an operation on that
template's output, Helm has a special include
function:
{{ include "toYaml" $value | indent 2 }}
The above includes a template called toYaml
, passes it $value
, and then
passes the output of that template to the indent
function.
Because YAML ascribes significance to indentation levels and whitespace, this is one great way to include snippets of code, but handle indentation in a relevant context.
'required' 함수 사용하기
Go provides a way for setting template options to control behavior when a map is
indexed with a key that's not present in the map. This is typically set with
template.Options("missingkey=option")
, where option
can be default
,
zero
, or error
. While setting this option to error will stop execution with
an error, this would apply to every missing key in the map. There may be
situations where a chart developer wants to enforce this behavior for select
values in the values.yaml
file.
The required
function gives developers the ability to declare a value entry as
required for template rendering. If the entry is empty in values.yaml
, the
template will not render and will return an error message supplied by the
developer.
For example:
{{ required "A valid foo is required!" .Values.foo }}
The above will render the template when .Values.foo
is defined, but will fail
to render and exit when .Values.foo
is undefined.
'tpl' 함수 사용하기
The tpl
function allows developers to evaluate strings as templates inside a
template. This is useful to pass a template string as a value to a chart or
render external configuration files. Syntax: {{ tpl TEMPLATE_STRING VALUES }}
Examples:
# values
template: "{{ .Values.name }}"
name: "Tom"
# template
{{ tpl .Values.template . }}
# output
Tom
Rendering an external configuration file:
# external configuration file conf/app.conf
firstName={{ .Values.firstName }}
lastName={{ .Values.lastName }}
# values
firstName: Peter
lastName: Parker
# template
{{ tpl (.Files.Get "conf/app.conf") . }}
# output
firstName=Peter
lastName=Parker
이미지 풀 시크릿 생성하기
Image pull secrets are essentially a combination of registry, username, and
password. You may need them in an application you are deploying, but to
create them requires running base64
a couple of times. We can write a helper
template to compose the Docker configuration file for use as the Secret's
payload. Here is an example:
First, assume that the credentials are defined in the values.yaml
file like
so:
imageCredentials:
registry: quay.io
username: someone
password: sillyness
email: someone@host.com
We then define our helper template as follows:
{{- define "imagePullSecret" }}
{{- with .Values.imageCredentials }}
{{- printf "{\"auths\":{\"%s\":{\"username\":\"%s\",\"password\":\"%s\",\"email\":\"%s\",\"auth\":\"%s\"}}}" .registry .username .password .email (printf "%s:%s" .username .password | b64enc) | b64enc }}
{{- end }}
{{- end }}
Finally, we use the helper template in a larger template to create the Secret manifest:
apiVersion: v1
kind: Secret
metadata:
name: myregistrykey
type: kubernetes.io/dockerconfigjson
data:
.dockerconfigjson: {{ template "imagePullSecret" . }}
자동 디플로이먼트 전환(roll)
Often times ConfigMaps or Secrets are injected as configuration files in
containers or there are other external dependency changes that require rolling
pods. Depending on the application a restart may be required should those be
updated with a subsequent helm upgrade
, but if the deployment spec itself
didn't change the application keeps running with the old configuration resulting
in an inconsistent deployment.
The sha256sum
function can be used to ensure a deployment's annotation section
is updated if another file changes:
kind: Deployment
spec:
template:
metadata:
annotations:
checksum/config: {{ include (print $.Template.BasePath "/configmap.yaml") . | sha256sum }}
[...]
In the event you always want to roll your deployment, you can use a similar annotation step as above, instead replacing with a random string so it always changes and causes the deployment to roll:
kind: Deployment
spec:
template:
metadata:
annotations:
rollme: {{ randAlphaNum 5 | quote }}
[...]
Both of these methods allow your Deployment to leverage the built in update strategy logic to avoid taking downtime.
NOTE: In the past we recommended using the --recreate-pods
flag as another
option. This flag has been marked as deprecated in Helm 3 in favor of the more
declarative method above.
헬름에 리소스를 언인스톨하지 않도록 알리기
Sometimes there are resources that should not be uninstalled when Helm runs a
helm uninstall
. Chart developers can add an annotation to a resource to
prevent it from being uninstalled.
kind: Secret
metadata:
annotations:
"helm.sh/resource-policy": keep
[...]
(Quotation marks are required)
The annotation "helm.sh/resource-policy": keep
instructs Helm to skip deleting
this resource when a helm operation (such as helm uninstall
, helm upgrade
or
helm rollback
) would result in its deletion. However, this resource becomes
orphaned. Helm will no longer manage it in any way. This can lead to problems if
using helm install --replace
on a release that has already been uninstalled,
but has kept resources.
"Partials" 및 템플릿 포함(include) 사용하기
Sometimes you want to create some reusable parts in your chart, whether they're blocks or template partials. And often, it's cleaner to keep these in their own files.
In the templates/
directory, any file that begins with an underscore(_
) is
not expected to output a Kubernetes manifest file. So by convention, helper
templates and partials are placed in a _helpers.tpl
file.
의존성이 많은 복잡한 차트
Many of the charts in the official charts repository are "building blocks" for creating more advanced applications. But charts may be used to create instances of large-scale applications. In such cases, a single umbrella chart may have multiple subcharts, each of which functions as a piece of the whole.
The current best practice for composing a complex application from discrete
parts is to create a top-level umbrella chart that exposes the global
configurations, and then use the charts/
subdirectory to embed each of the
components.
YAML은 JSON의 상위집합이다
According to the YAML specification, YAML is a superset of JSON. That means that any valid JSON structure ought to be valid in YAML.
This has an advantage: Sometimes template developers may find it easier to express a datastructure with a JSON-like syntax rather than deal with YAML's whitespace sensitivity.
As a best practice, templates should follow a YAML-like syntax unless the JSON syntax substantially reduces the risk of a formatting issue.
랜덤 값을 생성할 때는 주의하자
There are functions in Helm that allow you to generate random data, cryptographic keys, and so on. These are fine to use. But be aware that during upgrades, templates are re-executed. When a template run generates data that differs from the last run, that will trigger an update of that resource.
하나의 명령어로 설치 또는 업그레이드하기
Helm provides a way to perform an install-or-upgrade as a single command. Use
helm upgrade
with the --install
command. This will cause Helm to see if the
release is already installed. If not, it will run an install. If it is, then the
existing release will be upgraded.
$ helm upgrade --install <release name> --values <values file> <chart directory>