Alerts firing on Prometheus but not on Alertmanager - monitoring

Question

I can't seem to find out why Alertmanager is not getting alerts from Prometheus. I would appreciate a swift assistance on this challenge. I'm fairly new with using Prometheus and Alertmanager. I am using a webhook for MsTeams to push the notifications from alertmanager.
Alertmanager.yml
global:
resolve_timeout: 5m
route:
group_by: ['critical','severity']
group_wait: 10s
group_interval: 10s
repeat_interval: 1h
receiver: 'alert_channel'
receivers:
- name: 'alert_channel'
webhook_configs:
- url: 'http://localhost:2000/alert_channel'
send_resolved: true
prometheus.yml - (Just a part of it)
# my global config
global:
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.
# scrape_timeout is set to the global default (10s).
# Alertmanager configuration
alerting:
alertmanagers:
- static_configs:
- targets:
- localhost:9093
# Load rules once and periodically evaluate them according to the global 'evaluation_interval'.
rule_files:
# - "first_rules.yml"
# - "second_rules.yml"
- alert_rules.yml
# A scrape configuration containing exactly one endpoint to scrape:
# Here it's Prometheus itself.
scrape_configs:
# The job name is added as a label `job=<job_name>` to any timeseries scraped from this config.
- job_name: 'kafka'
# metrics_path defaults to '/metrics'
# scheme defaults to 'http'
static_configs:
- targets: ['localhost:8080']
labels:
service: 'Kafka'
alertmanager.service
[Unit]
Description=Prometheus Alert Manager
Wants=network-online.target
After=network-online.target
[Service]
Type=simple
User=alertmanager
Group=alertmanager
ExecStart=/usr/local/bin/alertmanager \
--config.file=/etc/alertmanager/alertmanager.yml \
--storage.path=/data/alertmanager \
--web.listen-address=127.0.0.1:9093
Restart=always
[Install]
WantedBy=multi-user.target
alert_rules
groups:
- name: alert_rules
rules:
- alert: ServiceDown
expr: up == 0
for: 1m
labels:
severity: "critical"
annotations:
summary: "Service {{ $labels.service }} down!"
description: "{{ $labels.service }} of job {{ $labels.job }} has been down for more than 1 minute."
- alert: HostOutOfMemory
expr: node_memory_MemAvailable_bytes / node_memory_MemTotal_bytes * 100 < 25
for: 5m
labels:
severity: warning
annotations:
summary: "Host out of memory (instance {{ $labels.instance }})"
description: "Node memory is filling up (< 25% left)\n VALUE = {{ $value }}\n LABELS: {{ $labels }}"
- alert: HostOutOfDiskSpace
expr: (node_filesystem_avail_bytes{mountpoint="/"} * 100) / node_filesystem_size_bytes{mountpoint="/"} < 40
for: 1s
labels:
severity: warning
annotations:
summary: "Host out of disk space (instance {{ $labels.instance }})"
description: "Disk is almost full (< 40% left)\n VALUE = {{ $value }}\n LABELS: {{ $labels }}"
Prometheus Alerts
But I don't see those alerts on alertmanager
I'm out of ideas at this point. Please I need help. I've been on this since last week.

Answer 1

You have a mistake in your Alertmanager configuration. group_by expects a collection of label names and from what I am seeing critical is a label value, not the name. So simply remove critical and you should be good to go.
Also check out this blog posts, quite helpful https://www.robustperception.io/whats-the-difference-between-group_interval-group_wait-and-repeat_interval
Edit 1
If you want the receiver alert_channel to only receive alerts that have the severity critical you have to create a route and with a match attribute.
Something along these lines:
route:
group_by: ['...'] # good if very low volum
group_wait: 15s
group_interval: 5m
repeat_interval: 1h
routes:
- match:
- severity: critical
receiver: alert_channel
Edit 2
If this does not work as well try out this:
route:
group_by: ['...']
group_wait: 15s
group_interval: 5m
repeat_interval: 1h
receiver: alert_channel
This should work. Check your Prometheus logs and see if you find hints there