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How to create custom email template in Alertmanager?

Configure your email receiver to, for example, display the email's subject in the headers section and its template-based body of text.

- name: EmailReceiver
- to: myaddress@example.com
subject: 'Summary: {{ .CommonLabels.alertname }} {{ if eq .Status "firing" }}(Firing){{ else }}(Resolved){{ end }}'
html: '{{ template "emailcontent.txt" . }}'

As indicated below, add the section templates to your alertmanager.yaml configuration file.

- /etc/alertmanager/config/custom_mail.tmpl

Mount the custom mail.tmpl file in the alertmanager pod at /etc/alertmanager/config. Please take note that the define clause should exactly match the email recipient's html section:

{{ define ""emailcontent.txt" }} ... <content of the email> ... {{ end}}

Mount this file in the alertmanager pod, at /etc/alertmanager/config. Get the base64 encoded content of the file.

cat custom_mail.tmpl | base64 -w 0

Insert this in the alertmanager-main secret.

oc edit -n openshift-monitoring edit secret alertmanager-main

Add the below section.

apiVersion: v1
alertmanager.yaml: Imdsb2JhbCI6CiAgInJlc29sdmVfdGltZW91dCI6ICI1bSIK....
custom_mail.tmpl: <content from former step>

check the file has been mounted in alertmanager pod.

oc -n openshift-monitoring exec alertmanager-main-0 -- ls -l /etc/alertmanager/config
total 0
lrwxrwxrwx. 1 root nobody 24 Oct 18 14:59 alertmanager.yaml -> ..data/alertmanager.yaml
lrwxrwxrwx. 1 root nobody 15 Oct 18 14:59 custom_mail.tmpl -> ../data/custom_mail.tmpl

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