Demo Prometheus Alert Manager Installation

In this guide, you’ll install Alertmanager on a Linux VM and configure it to send alerts directly to Slack. We’ll cover downloading the binary, inspecting defaults, setting up Slack webhooks, and reloading Alertmanager without downtime.

Prerequisites

• A Linux VM with internet access
• wget, tar, and curl installed
• A Slack workspace with permissions to create Incoming Webhooks

1. Download and Extract Alertmanager

Download the latest Alertmanager release (v0.22.2) and unpack it:

wget https://github.com/prometheus/alertmanager/releases/download/v0.22.2/alertmanager-0.22.2.linux-amd64.tar.gz
tar xzvf alertmanager-0.22.2.linux-amd64.tar.gz

Change into the directory and verify the contents:

cd alertmanager-0.22.2.linux-amd64/
ll

Expected output:

total 47796
-rwxr-xr-x 1 root root 27407406 Jun 27 07:51 alertmanager*
-rw-r--r-- 1 root root   1813684 Jun 27 07:52 alertmanager.yml
-rwxr-xr-x 1 root root     9340 Jun 27 15:56 amtool*
-rw-r--r-- 1 root root    4158 Jun 27 15:56 NOTICE
-rw-r--r-- 1 root root    1470 Jun 27 15:56 LICENSE

2. Inspect the Default Configuration

Open alertmanager.yml to review the default routing and inhibition settings:

route:
  group_by: ['alertname']
  group_wait: 30s
  group_interval: 5m
  repeat_interval: 1h
  receiver: 'web.hook'

receivers:
- name: 'web.hook'
  webhook_configs:
    - url: 'http://127.0.0.1:5001'

inhibit_rules:
- source_match:
    severity: 'critical'
  target_match:
    severity: 'warning'
  equal: ['alertname', 'dev', 'instance']

3. Start Alertmanager

Launch Alertmanager and confirm it listens on port 9093:

./alertmanager

You should see logs like:

level=info ts=2021-06-27T15:39:57.100Z caller=main.go:221 msg="Starting Alertmanager" version="(version=0.22.2, branch=HEAD, revision=...)"
level=info ts=2021-06-27T15:39:57.514 msg="Listening address=:9093"
level=info ts=2021-06-27T15:39:57.514 msg="TLS is disabled." http2=false

Open your browser at http://<VM_PUBLIC_DNS>:9093 to verify the UI.

4. Configure Slack Notifications

To route alerts to Slack, update alertmanager.yml with your workspace’s Incoming Webhook URL.

Below is a sample Slack configuration—replace <YOUR_SLACK_WEBHOOK_URL> with your actual webhook URL and adjust the channel as needed:

global:
  resolve_timeout: 1m
  slack_api_url: '<YOUR_SLACK_WEBHOOK_URL>'

route:
  receiver: 'slack-notifications'
  group_by: ['alertname', 'datacenter', 'app']
  group_wait: 30s
  group_interval: 5m
  repeat_interval: 1h

receivers:
  - name: 'slack-notifications'
    slack_configs:
      - send_resolved: true
        api_url: '<YOUR_SLACK_WEBHOOK_URL>'
        channel: '#alerts'
        username: '{{ template "slack.default.username" . }}'
        color: '{{ if eq .Status "firing" }}danger{{ else }}good{{ end }}'
        title: >
          {{ $status := .Status | toUpper }}{{ if eq $status "FIRING" }}:{{ .Alerts.Firing | len }}{{ end }} {{ .CommonLabels.alertname }} for {{ .CommonLabels.job }}
        text: |
          {{ range .Alerts -}}
          *Alert:* {{ .Annotations.summary }}  
          *Description:* {{ .Annotations.description }}  
          {{ end }}
        short_fields: false
        footer: '{{ template "slack.default.footer" . }}'
        icon_emoji: '{{ template "slack.default.iconemoji" . }}'

Create a Slack Incoming Webhook

1. In Slack, Create an App (e.g., “Prometheus Alerting”).
2. Enable Incoming Webhooks and add a webhook to your target channel.
3. Copy the generated URL and insert it in both slack_api_url and api_url above.
4. Save alertmanager.yml.

5. Reload Alertmanager Configuration

Reload without downtime by sending an HTTP POST:

curl -X POST http://localhost:9093/-/reload

Refresh the UI (http://<VM_PUBLIC_DNS>:9093) to confirm your Slack receiver is active.

Next Steps

• Configure Prometheus to forward alerts to Alertmanager
• Define custom alerting rules in Prometheus
• Explore advanced routing and inhibition in Alertmanager

Links and References

• Prometheus Alertmanager Docs
• Slack Incoming Webhooks