Documentation Grafana Cloud Instrument and send data Grafana Alloy Monitor metrics and logs Monitor log files

Monitor logs from a local file with Grafana Alloy

Log files record events, activities, and usage patterns within a system, application, or network. These files are essential for monitoring, troubleshooting, and understanding system behavior. With Alloy, you can collect your logs, forward them to a Grafana stack, and create dashboards to monitor your system behavior.

The alloy-scenarios repository contains complete examples of Alloy deployments. Clone the repository and use the examples to understand how Alloy collects, processes, and exports telemetry signals.

In this example scenario, Alloy collects logs from a local file and forwards them to a Loki destination.

Before you begin

Ensure you have the following:

• Docker
• Git

Clone and deploy the example

Follow these steps to clone the scenarios repository and deploy the monitoring example:

1. Clone the Alloy scenarios repository.

   shell Copy

   git clone https://github.com/grafana/alloy-scenarios.git

2. Start Docker to deploy the Grafana stack.

   shell Copy

   cd alloy-scenarios/logs-file
   docker compose up -d

   Verify the status of the Docker containers:

   shell Copy

   docker ps

3. (Optional) Stop Docker to shut down the Grafana stack when you finish exploring this example.

   shell Copy

   docker compose down

Monitor and visualize your data

Use Grafana to monitor your deployment’s health and visualize your data.

Monitor Alloy

To monitor the health of your Alloy deployment, open your browser and go to http://localhost:12345.

For more information about the Alloy UI, refer to Debug Grafana Alloy.

Visualize your data

To use the Grafana Logs Drilldown, open your browser and go to http://localhost:3000/a/grafana-lokiexplore-app.

To create a dashboard for visualizing metrics and logs, open your browser and go to http://localhost:3000/dashboards.

Understand the Alloy configuration

This example uses a config.alloy file to configure the Alloy components for logging. You can find this file in the cloned repository at alloy-scenarios/logs-file/.

The configuration includes livedebugging to stream real-time data to the Alloy UI.

Configure livedebugging

livedebugging streams real-time data from your components directly to the Alloy UI. Refer to the Troubleshooting documentation for more details about this feature.

livedebugging

By default, livedebugging is disabled. Enable it explicitly through the livedebugging configuration block to make debugging data visible in the Alloy UI.

alloy Copy

livedebugging {
  enabled = true
}

Configure logging

The logging configuration in this example requires three components:

• local.file_match
• loki.source.file
• loki.write

local.file_match

The local.file_match component discovers files on the local filesystem using glob patterns. In this example, the component requires the following arguments:

• path_targets: Targets to expand. Looks for glob patterns on the __path__ key.
• sync_period: How often to sync the filesystem and targets.

alloy Copy

local.file_match "local_files" {
    path_targets = [{"__path__" = "/temp/logs/*.log", "job" = "python", "hostname" = constants.hostname}]
    sync_period  = "5s"
}

loki.source.file

The loki.source.file component reads log entries from files and forwards them to other Loki components. In this example, the component requires the following arguments:

• targets: The list of files to read logs from.
• forward_to: The list of receivers to send log entries to.
• tail_from_end: Whether a log file is tailed from the end if a stored position isn’t found.

alloy Copy

loki.source.file "log_scrape" {
    targets    = local.file_match.local_files.targets
    forward_to = [loki.write.local.receiver]
    tail_from_end = true
}

loki.write

The loki.write component writes logs to a Loki destination. In this example, the component requires the following argument:

• url: Defines the full URL endpoint in Loki to send logs to.

alloy Copy

loki.write "local" {
  endpoint {
    url = "http://loki:3100/loki/api/v1/push"
  }
}