为什么helm模板函数不解析$labels var？

Question

我定义一个PrometheusRule如下：

prometheusRule:
  rules:
    - alert: SSLCertExpiringSoon
      expr: probe_ssl_earliest_cert_expiry - time() < 86400 * 10
      for: 0m
      labels:
        severity: warning
      annotations:
        summary: Blackbox SSL certificate will expire soon (instance {{ $labels.instance }})
        description: "SSL certificate expires in 30 days\n  VALUE = {{ $value }}\n  LABELS = {{ $labels }}"

以及头盔图中的模板yml：

{{- if .Values.prometheusRule.enabled }}
apiVersion: monitoring.coreos.com/v1
kind: PrometheusRule
metadata:
  name: {{ template "prometheus-blackbox-exporter.fullname" . }}
  {{- with .Values.prometheusRule.namespace }}
  namespace: {{ . }}
  {{- end }}
  labels:
    {{- include "prometheus-blackbox-exporter.labels" . | nindent 4 }}
    {{- with .Values.prometheusRule.additionalLabels -}}
{{- toYaml . | nindent 4 -}}
    {{- end }}
spec:
  {{- with .Values.prometheusRule.rules }}
  groups:
    - name: {{ template "prometheus-blackbox-exporter.name" $ }}
      rules: {{ tpl (toYaml .) $ | nindent 8 }}
  {{- end }}
{{- end }}

当我运行helm template时，tpl功能不是解析$labels和$values vars。当我删除注释时，舵机模板就不再抱怨了。哪里失败了？

错误：

Error: template: prometheus-blackbox-exporter/templates/prometheusrule.yaml:18:16: executing "prometheus-blackbox-exporter/templates/prometheusrule.yaml" at <tpl (toYaml .) $>: error calling tpl: error during tpl function execution for "- alert: SSLCertExpiringSoon\n  annotations:\n    summary: Blackbox SSL certificate will expire soon (instance {{ $labels.instance\n      }})\n  expr: probe_ssl_earliest_cert_expiry - time() < 86400 * 10\n  for: 0m\n  labels:\n    release: prometheus\n    severity: warning\n- alert: SSLCertExpiringSoon\n  annotations: null\n  expr: probe_ssl_earliest_cert_expiry - time() < 86400 * 3\n  for: 0m\n  labels:\n    severity: critical": parse error at (prometheus-blackbox-exporter/templates/prometheusrule.yaml:3): undefined variable "$labels"

Answer 1

普罗米修斯的报警规则也使用{{ ... $variable ... }}语法，类似于Helm，但与语法相似。当您通过tpl传递此文件时，Helm将尝试计算嵌入的{{ ... }}模板并计算其中的任何块。因为$labels和$value不是在Helm级别上定义的局部变量，所以您将得到这个错误。

如果您只想让Prometheus看到这个文件的原样，并且不需要在Helm级别替换任何东西(该文件不包括对.Values的引用)，那么您就不需要tpl了。

      rules: {{ toYaml . | nindent 8 }}

如果您确实需要tpl，那么在包含的文件中，需要将{{作为字符串发出，而不是作为模板处理。其中一种语法方法是创建一个模板块，打印出{{。

description: "VALUE = {{ "{{" }} $value }}"
#                     ^^^^^^^^^^ a {{ ... }} block that prints "{{"

Answer 2

语法的工作版本如下：

{{ `{{` }} $value }}