# Setting up Prometheus Alertmanager integration via matrix-alertmanager-receiver (optional)

The playbook can install and configure the [matrix-alertmanager-receiver](https://github.com/metio/matrix-alertmanager-receiver) service for you. It's a [client](https://prometheus.io/docs/alerting/latest/clients/) for Prometheus' [Alertmanager](https://prometheus.io/docs/alerting/latest/alertmanager/), allowing you to deliver alerts to Matrix rooms.

See the project's [documentation](https://github.com/metio/matrix-alertmanager-receiver/blob/main/README.md) to learn what it does and why it might be useful to you.

This service is meant to be used with an external [Alertmanager](https://prometheus.io/docs/alerting/latest/alertmanager/) instance. It's **not** meant to be integrated with the [Prometheus & Grafana stack](./configuring-playbook-prometheus-grafana.md) installed by this playbook, because the Alertmanager component is not installed by it.

## Prerequisites

### Register the bot account

This service uses a bot (with a username specified in `matrix_alertmanager_receiver_config_matrix_user_id_localpart`) for delivering messages.

The playbook does not automatically create users for you. You **need to register the bot user manually** before setting up the bot.

Choose a strong password for the bot. You can generate a good password with a command like this: `pwgen -s 64 1`.

You can use the playbook to [register a new user](registering-users.md):

```sh
ansible-playbook -i inventory/hosts setup.yml --extra-vars='username=bot.alertmanager.receiver password=PASSWORD_FOR_THE_BOT admin=no' --tags=register-user
```

### Get an access token

The bot requires an access token to be able to connect to your homeserver. Refer to the documentation on [how to obtain an access token](obtaining-access-tokens.md).

### Join to rooms as the bot manually

ℹ️ **This bot does not accept room invitations automatically**. To deliver messages to rooms, the bot must be joined to all rooms manually.

For each new room you would like the bot to deliver alerts to, invite the bot to the room.

Then, log in as the bot using any Matrix client of your choosing, accept the room invitation from the bot's account, and log out.

## Adjusting the playbook configuration

Add the following configuration to your `inventory/host_vars/matrix.example.com/vars.yml` file. Make sure to replace `ACCESS_TOKEN_HERE` with the one created [above](#get-an-access-token).

```yaml
matrix_alertmanager_receiver_enabled: true

# Uncomment and adjust this part if you'd like to use a username different than the default
# matrix_alertmanager_receiver_config_matrix_user_id_localpart: "bot.alertmanager.receiver"

# Specify the bot user's access token here.
matrix_alertmanager_receiver_config_matrix_access_token: "ACCESS_TOKEN_HERE"

# Optionally, configure some mappings (URL-friendly room name -> actual Matrix room ID).
#
# If you don't configure mappings, you can still deliver alerts using URLs like this:
# https://matrix.example.com/matrix-alertmanager-receiver-RANDOM_VALUE_HERE/alert/!qporfwt:example.com
#
# If a mapping like the one below is configured, you can deliver alerts using friendlier URLs like this:
# https://matrix.example.com/matrix-alertmanager-receiver-RANDOM_VALUE_HERE/alert/some-room-name
matrix_alertmanager_receiver_config_matrix_room_mapping:
  some-room-name: "!qporfwt:{{ matrix_domain }}"
```

See `roles/custom/matrix-alertmanager-receiver/defaults/main.yml` for additional configuration variables.

### Adjusting the matrix-alertmanager-receiver URL

By default, this playbook installs matrix-alertmanager-receiver on the `matrix.` subdomain, at the `/matrix-alertmanager-receiver` path (https://matrix.example.com/matrix-alertmanager-receiver). This makes it easy to install it, because it **doesn't require additional DNS records to be set up**. If that's okay, you can skip this section.

By tweaking the `matrix_alertmanager_receiver_hostname` and `matrix_alertmanager_receiver_path_prefix` variables, you can easily make the service available at a **different hostname and/or path** than the default one.

Example additional configuration for your `inventory/host_vars/matrix.example.com/vars.yml` file:

```yaml
# Change the default hostname and path prefix
matrix_alertmanager_receiver_hostname: alertmanager.example.com
matrix_alertmanager_receiver_path_prefix: /
```

## Adjusting DNS records

If you've changed the default hostname, **you may need to adjust your DNS** records to point the matrix-alertmanager-receiver domain to the Matrix server.

See [Configuring DNS](configuring-dns.md) for details about DNS changes.

If you've decided to use the default hostname, you won't need to do any extra DNS configuration.

## Installing

After configuring the playbook and potentially [adjusting your DNS records](#adjusting-dns-records), run the playbook with [playbook tags](playbook-tags.md) as below:

<!-- NOTE: let this conservative command run (instead of install-all) to make it clear that failure of the command means something is clearly broken. -->
```sh
ansible-playbook -i inventory/hosts setup.yml --tags=setup-all,ensure-matrix-users-created,start
```

**Notes**:

- The `ensure-matrix-users-created` playbook tag makes the playbook automatically create the bot's user account.

- The shortcut commands with the [`just` program](just.md) are also available: `just install-all` or `just setup-all`

  `just install-all` is useful for maintaining your setup quickly ([2x-5x faster](../CHANGELOG.md#2x-5x-performance-improvements-in-playbook-runtime) than `just setup-all`) when its components remain unchanged. If you adjust your `vars.yml` to remove other components, you'd need to run `just setup-all`, or these components will still remain installed.

## Usage

Configure your Prometheus Alertmanager with configuration like this:

```yaml
receivers:
  - name: matrix
    webhook_configs:
      - send_resolved: true
        url: URL_HERE
route:
  group_by:
    - namespace
  group_interval: 5m
  group_wait: 30s
  receiver: "matrix"
  repeat_interval: 12h
  routes:
    - receiver: matrix
```

where `URL_HERE` looks like `https://matrix.example.com/matrix-alertmanager-receiver-RANDOM_VALUE_HERE/alert/some-room-name` or `https://matrix.example.com/matrix-alertmanager-receiver-RANDOM_VALUE_HERE/alert/!qporfwt:example.com`.
