为什么 helm 模板函数不解析 $labels var？

Question

我正在定义一个 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 helm chart 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、tpl func 时，它没有解析 $labels 和 $values 变量。当我删除注释时，helm 模板不再抱怨。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

Prometheus's alerting rules also use {{ ... $variable ... }} syntax, similar to Helm but with a different variant on the Go text/template syntax。当您通过 tpl 传递此文件时，Helm 会尝试评估嵌入的 {{ ... }} 模板并评估那里的任何块。由于 $labels 和 $value 不是在 Helm 级别定义的局部变量，因此您会收到此错误。

如果您只想让 Prometheus 按原样查看此文件，并且不需要在 Helm 级别替换任何内容（该文件不包含对 .Values 的引用），那么您不需要不需要 tpl

      rules: {{ toYaml . | nindent 8 }}

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

的模板块

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

Answer 2

语法的工作版本如下：

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

为什么 helm 模板函数不解析 $labels var？

Why helm template function is not resolveing $labels var?

go-templates

kubernetes-helm