Configure Prometheus Email Alerting with AlertManager

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In this tutorial, you will learn how to configure Prometheus Email alerting with AlertManager. AlertManager is used to handle alerts sent by client applications such as the Prometheus server. It takes care of deduplicating, grouping, and routing them to the correct receiver integration such as email, PagerDuty, or OpsGenie. It also takes care of silencing and inhibition of alerts.

There is more to Prometheus! Check the link below;

Prometheus: Up & Running: Infrastructure and Application Performance Monitoring

Configuring Prometheus Email Alerting with AlertManager

In our previous guide, we learnt how to monitor SSL/TLS certificate expiry using Prometheus and Grafana.

We integrated Telegraf with Prometheus for SSL/TLS certificate.

check ssl monitoring telegraf

From the above screenshot, you can see that you have 2591897 seconds, which is equivalent to ~30 days (a month) before the certificate expires.

With that duration of time, one might end up forgetting that SSL/TLS certificates expires and hence may forget to renew the certificate. That is why it is important to configure Prometheus Email alerting such that, when a few days are due for certificate renewal, you can be notified via email.

So, assuming that you already have Prometheus up and running, how can you use AlertMnager to configure Prometheus Email alerting?

Therefore, open Prometheus configuration file and set alertmanager configurations, the Promtheus alert rules files as shown below;

vim /etc/prometheus/prometheus.yml

Update the lines below accordingly;

# Alertmanager configuration
  - static_configs:
    - targets:
       - localhost:9093

# Load rules once and periodically evaluate them according to the global 'evaluation_interval'.
   - "alert_rules.yml"

Without comment lines, this is how our Prometheus configuration file looks like;

  scrape_interval:     15s # Set the scrape interval to every 15 seconds. Default is every 1 minute.
  evaluation_interval: 15s # Evaluate rules every 15 seconds. The default is every 1 minute.
  - static_configs:
    - targets:
       - localhost:9093
   - "alert_rules.yml"
  - job_name: 'prometheus'
    - targets: ['localhost:9090']
  - job_name: 'SSL/TLS Certs'
    - targets: ['']

Save and exit the configuration file.

Create Prometheus Alert Rules

Alerting rules allow you to define alert conditions based on Prometheus expression language expressions and to send notifications about firing alerts to an external service. Whenever the alert expression results in one or more vector elements at a given point in time, the alert counts as active for these elements’ label sets“.

In our configuration file, we defined the Prometheus rules file as alert_rules.yml. This file should reside within the Prometheus configurations directory, /etc/prometheus.

Hence, create the rules file with the content similar to below;

vim /etc/prometheus/alert_rules.yml

Note that in this example, we will be creating rule to alert us when the SSL/TLS certificate is due to expire in a few days.

As shown above, we have a certificate that is due for renewal in the next 30 days. To make this demo easy, we will create a rule to alert when have 30 or less days to certificate renewal.

- name: alert_rules
  - alert: SSL_TLS_Cert_Expiry
    expr: x509_cert_expiry{job="SSL/TLS Certs"} <= 2592000 
    for: 1m
      severity: critical
      summary: SSL/TLS Certificate Expiry

Various setting values have been explained here.

Save and exit the file.

Check if the rule files are valid or not;

promtool check rules /etc/prometheus/alert_rules.yml
Checking /etc/prometheus/alert_rules.yml
  SUCCESS: 1 rules found

If you check on Prometheus web interface Rules page;

Configure Prometheus Email Alerting with AlertManager

Install and Configure AlertManager

Install AlertManager

AlertManager can be installed using pre-compiled binaries that can be downloaded from Prometheus downloads section.

Hence, before you can install AlertManager;

Create AlertManager system user and group as shown below;

useradd -M -r -s /bin/false alertmanager

Next, navigate to the downloads section and grab the latest version of AlertManager. You simply use wget to download it. The current release version as of this writing is 0.21.0.


Extract the downloaded binary;

tar xzf alertmanager-0.21.0.linux-amd64.tar.gz

Copy the AlertManager binary files, alertmanager and amtool to binary directory like /usr/local/bin/.

cp alertmanager-0.21.0.linux-amd64/{alertmanager,amtool} /usr/local/bin/

Next, create a configuration directory for AlertManager and copy the YAML configuration to that directory;

cp alertmanager-0.21.0.linux-amd64/alertmanager.yml /etc/alertmanager/

Set the ownership of the AlertManager configuration directory and the binaries to alertmanager user created above;

chown alertmanager: /etc/alertmanager/alertmanager.yml /usr/local/bin/{alertmanager,amtool}

Configure AlertManager

In this setup, we will be sending the alerts via Email and we will use Gmail relay in that case.

Hence, configure AlertManager as follows;

vim /etc/alertmanager/alertmanager.yml
  resolve_timeout: 5m

  group_by: ['alertname']
  group_wait: 10s
  group_interval: 10s
  repeat_interval: 24h
  receiver: 'email'
- name: 'email'
  - to: '[email protected]'
    from: '[email protected]'
    auth_username: '[email protected]'
    auth_identity: '[email protected]'
    auth_password: 'password'

Save and exit the configuration file. Be sure to set the email settings appropriately.

More about the config on configuration page and git repo page.

Check the Alertmanager configuration file to validate it.

amtool check-config /etc/alertmanager/alertmanager.yml
Checking '/etc/alertmanager/alertmanager.yml'  SUCCESS
 - global config
 - route
 - 0 inhibit rules
 - 1 receivers
 - 0 templates

Running AlertManager

You can run Alertmanager in standalone mode by executing the command below;

alertmanager --config.file /etc/alertmanager/alertmanager.yml

Remember, we set Prometheus to connect to Alertmanager via localhost:9093, hence replace the x.x.x.x with the correct address.

To run AlertManager as a service;

cat > /etc/systemd/system/alertmanager.service << 'EOL'
Description=AlertManager Server Service

ExecStart=/usr/local/bin/alertmanager --config.file /etc/alertmanager/alertmanager.yml


For other options, consult /usr/local/bin/alertmanager --help.

Reload systemd configurations and start Alertmanager;

systemctl daemon-reload
systemctl enable --now alertmanager

Check the status;

systemctl status alertmanager
● alertmanager.service - AlertManager Server Service
   Loaded: loaded (/etc/systemd/system/alertmanager.service; enabled; vendor preset: enabled)
   Active: active (running) since Sat 2021-04-10 23:16:25 EAT; 1s ago
 Main PID: 3959 (alertmanager)
    Tasks: 8 (limit: 2359)
   Memory: 13.5M
   CGroup: /system.slice/alertmanager.service
           └─3959 /usr/local/bin/alertmanager --config.file /etc/alertmanager/alertmanager.yml --web.external-url=http://localhost:9093

Apr 10 23:16:25 debian systemd[1]: Started AlertManager Server Service.
Apr 10 23:16:25 debian alertmanager[3959]: level=info ts=2021-04-10T20:16:25.745Z caller=main.go:485 msg=Listening address=:9093

Check Prometheus Alerts page;

prometheus alertmanager alerts firing

Also check your mail;

alertmanager email alert

You can further customize the email template.

You can also view alerts in Alertmanager, http://x.x.x.x:9093/alerts;

Alertmanager alerts

Further Reading

AlertManager overview

Other Tutorials

Monitor SSL/TLS Certificates Expiry with Nagios

Monitor Linux System Metrics with Prometheus Node Exporter

Monitoring Gitlab Metrics with Prometheus and Grafana

Monitor OpenVPN Connections with Prometheus and Grafana

Install OpenNMS Network Monitoring tool on Ubuntu 20.04


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3 thoughts on “Configure Prometheus Email Alerting with AlertManager”

  1. Hello,
    thanks for this tutorial.

    I have setup Prometheus + AlertManager successfully.
    However I failed to configure AlterManager to send notification via Email to different receivers, means I have e.g. 2 different alerts and I want to send it to different receives.

    Can you please advise how to configure this?


  2. Hi gen_too. You mentioned “You can further customize the email template.” Do you know how exactly? I’m using prometheus-community helm chart.


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