# Monitoring multiple Linux hosts with Grafana Agent Role

Monitoring with Grafana Agents across multiple Linux hosts can be difficult.
To make it easier, you can use the Grafana Agent role with the Grafana Ansible collection.
This guide shows how to use the `grafana_agent` Ansible role to deploy and manage Grafana Agents across multiple Linux hosts so you can monitor them in Grafana.

## Before you begin

Before you begin, you should have:

- Linux hosts
- SSH access to the Linux hosts
- Account permissions sufficient to install and use Grafana Agent on the Linux hosts

## Install the Grafana Ansible collection

The [Grafana Agent role](https://github.com/grafana/grafana-ansible-collection/tree/main/roles/grafana_agent) is available in the Grafana Ansible collection as of the 1.1.0 release.

To install the Grafana Ansible collection, run this command:

```
ansible-galaxy collection install grafana.grafana:2.0.0
```

## Create an Ansible inventory file

Next, you will set up your hosts and create an inventory file.

1. Create your hosts and add public SSH keys to them.

  This example uses eight Linux hosts: two Ubuntu hosts, two CentOS hosts, two Fedora hosts, and two Debian hosts.

1. Create an Ansible inventory file.

  The Ansible inventory, which resides in a file named `inventory`, looks similar to this:

  ```
  146.190.208.216    # hostname = ubuntu-01
  146.190.208.190    # hostname = ubuntu-02
  137.184.155.128    # hostname = centos-01
  146.190.216.129    # hostname = centos-02
  198.199.82.174     # hostname = debian-01
  198.199.77.93      # hostname = debian-02
  143.198.182.156    # hostname = fedora-01
  143.244.174.246    # hostname = fedora-02
  ```

  > **Note**: If you are copying the above file, remove the comments (#).

1. Create an `ansible.cfg` file within the same directory as `inventory`, with the following values:
  ```
  [defaults]
  inventory = inventory  # Path to the inventory file
  private_key_file = ~/.ssh/id_rsa   # Path to my private SSH Key
  remote_user=root
  ```

## Use the Grafana Agent Ansible role

Next you will create an Ansible playbook that calls the `grafana_agent` role from the `grafana.grafana` Ansible collection.

To use the Grafana Agent Ansible role:

1. Create a file named `deploy-agent.yml` in the same directory as `ansible.cfg` and `inventory` and add the configuration below.

  ```yaml
    - name: Install Grafana Agent
      hosts: all
      become: true
    
      vars:
        grafana_cloud_api_key: <Your Grafana.com API Key>        # Example - eyJrIjoiYjI3NjI5MGQxZTcyOTIxYTc0MDgzMGVhNDhlODNhYzA5OTk2Y2U5YiIsIm4iOiJhbnNpYmxldGVzdCIsImlkIjo2NTI5
        metrics_username: <prometheus-username>                  # Example - 825019
        logs_username: <loki-username>                           # Example - 411478
        prometheus_url: <prometheus-push-url>                    # Example - https://prometheus-us-central1.grafana.net/api/prom/push
        loki_url: <loki-push-url>                                # Example - https://logs-prod-017.grafana.net/loki/api/v1/push
      tasks: 
        - name: Install Grafana Agent
          ansible.builtin.include_role:
            name: grafana.grafana.grafana_agent
          vars:
            grafana_agent_metrics_config:
              configs:
                - name: integrations
                  remote_write:
                    - basic_auth:
                        password: "{{ grafana_cloud_api_key }}"
                        username: "{{ metrics_username }}"
                      url: "{{ prometheus_url }}"

              global:
                scrape_interval: 60s
              wal_directory: /tmp/grafana-agent-wal

            grafana_agent_logs_config:
              configs:
                - name: default
                  clients:
                    - basic_auth:
                        password: "{{ grafana_cloud_api_key }}"
                        username: "{{ logs_username }}"
                      url: "{{ loki_url }}"
                  positions:
                    filename: /tmp/positions.yaml
                  target_config:
                    sync_period: 10s
                  scrape_configs:
                    - job_name: varlogs
                      static_configs:
                        - targets: [localhost]
                          labels:
                            instance: ${HOSTNAME:-default}
                            job: varlogs
                            __path__: /var/log/*log
            grafana_agent_integrations_config:
              node_exporter:
                enabled: true
                instance: ${HOSTNAME:-default}
              prometheus_remote_write:
                - basic_auth:
                    password: "{{ grafana_cloud_api_key }}"
                    username: "{{ metrics_username }}"
                  url: "{{ prometheus_url }}"
  ```

  The playbook calls the `grafana_agent` role from the `grafana.grafana` Ansible collection. 
  The Agent configuration in this playbook send metrics and logs from the linux hosts to your Prometheus and Loki data sources.

  Refer to the [Grafana Ansible documentation](https://github.com/grafana/grafana-ansible-collection/tree/main/roles/grafana_agent#role-variables) to understand the other variables you can pass to the `grafana_agent` role.

  When deploying the Agent across multiple instances for monitoring them, It is essential that the Agent is able to auto-detect the hostname for ease in monitoring.
  Notice that the label `instance` has been set to the value `${HOSTNAME:-default}`, which is substituted by the value of the HOSTNAME environment variable in the Linux host.
  To read more about the variable substitution, refer to the Grafana Agent [node_exporter_config](https://grafana.com/docs/agent/latest/configuration/integrations/node-exporter-config/) documentation.

1. To run the playbook, run this command:

  ```
  ansible-playbook deploy-agent.yml
  ```

  > **Note:** You can place the `deploy-agent.yml`, `ansible.cfg` and `inventory` files in different directories based on your needs.

## Check that logs and metrics are being ingested into Prometheus and Loki

Logs and metrics will soon be available in Grafana if your Promtheus and Loki datasources are added.
To test this, use the Explore feature.
Click the Explore icon (compass icon) in the vertical navigation bar.

### Check logs

To check logs:

1. Use the dropdown menu at the top of the page to select your Loki logs data source.

1. In the log browser, run the query `{instance="centos-01"}` where centos-01 is the hostname of one of the Linux hosts.

  If you see log lines (shown in the example below), logs are being received.

  ![Logs](https://grafana.com/static/assets/img/blog/ansible-to-manage-agent1.png) 

  If no log lines appear, logs are not being collected.

### Check metrics

To check metrics:

1. Use the dropdown menu at the top of the page to select your Prometheus data source.

1. Run the query `{instance="centos-01"}` where centos-01 is the hostname of one of the Linux hosts.

  If you see a metrics graph and table (shown in the example below), metrics are being received.

  ![Metrics](https://grafana.com/static/assets/img/blog/ansible-to-manage-agent2.png)

  If no metrics appear, metrics are not being collected.

### View dashboards

Now that you have logs and metrics in Grafana, you can use dashboards to view them.
Here's an example of one of the prebuilt dashboards included with the Linux integration in Grafana Cloud:

![Dashboard](https://grafana.com/static/assets/img/blog/ansible-to-manage-agent3.png)

Using the **Instance** dropdown in the dashboard, you can select from the hostnames where you deployed Grafana Agent and start monitoring them.