Monitoring

Fluent Bit comes with built-it features to allow you to monitor the internals of your pipeline, connect to Prometheus and Grafana, Health checks and also connectors to use external services for such purposes:

• HTTP Server: JSON and Prometheus Exporter-style metrics

• Grafana Dashboards and Alerts

• Health Checks

• Calyptia Cloud: hosted service to monitor and visualize your pipelines

HTTP Server

Fluent Bit comes with a built-in HTTP Server that can be used to query internal information and monitor metrics of each running plugin.

The monitoring interface can be easily integrated with Prometheus since we support it native format.

Getting Started

To get started, the first step is to enable the HTTP Server from the configuration file:

[SERVICE]
    HTTP_Server  On
    HTTP_Listen  0.0.0.0
    HTTP_PORT    2020

[INPUT]
    Name cpu

[OUTPUT]
    Name  stdout
    Match *

the above configuration snippet will instruct Fluent Bit to start it HTTP Server on TCP Port 2020 and listening on all network interfaces:

$ bin/fluent-bit -c fluent-bit.conf
Fluent Bit v1.4.0
* Copyright (C) 2019-2020 The Fluent Bit Authors
* Copyright (C) 2015-2018 Treasure Data
* Fluent Bit is a CNCF sub-project under the umbrella of Fluentd
* https://fluentbit.io

[2020/03/10 19:08:24] [ info] [engine] started
[2020/03/10 19:08:24] [ info] [http_server] listen iface=0.0.0.0 tcp_port=2020

now with a simple curl command is enough to gather some information:

$ curl -s http://127.0.0.1:2020 | jq
{
  "fluent-bit": {
    "version": "0.13.0",
    "edition": "Community",
    "flags": [
      "FLB_HAVE_TLS",
      "FLB_HAVE_METRICS",
      "FLB_HAVE_SQLDB",
      "FLB_HAVE_TRACE",
      "FLB_HAVE_HTTP_SERVER",
      "FLB_HAVE_FLUSH_LIBCO",
      "FLB_HAVE_SYSTEMD",
      "FLB_HAVE_VALGRIND",
      "FLB_HAVE_FORK",
      "FLB_HAVE_PROXY_GO",
      "FLB_HAVE_REGEX",
      "FLB_HAVE_C_TLS",
      "FLB_HAVE_SETJMP",
      "FLB_HAVE_ACCEPT4",
      "FLB_HAVE_INOTIFY"
    ]
  }
}

Note that we are sending the curl command output to the jq program which helps to make the JSON data easy to read from the terminal. Fluent Bit don't aim to do JSON pretty-printing.

REST API Interface

Fluent Bit aims to expose useful interfaces for monitoring, as of Fluent Bit v0.14 the following end points are available:

Uptime Example

Query the service uptime with the following command:

$ curl -s http://127.0.0.1:2020/api/v1/uptime | jq

it should print a similar output like this:

{
  "uptime_sec": 8950000,
  "uptime_hr": "Fluent Bit has been running:  103 days, 14 hours, 6 minutes and 40 seconds"
}

Metrics Examples

Query internal metrics in JSON format with the following command:

$ curl -s http://127.0.0.1:2020/api/v1/metrics | jq

it should print a similar output like this:

{
  "input": {
    "cpu.0": {
      "records": 8,
      "bytes": 2536
    }
  },
  "output": {
    "stdout.0": {
      "proc_records": 5,
      "proc_bytes": 1585,
      "errors": 0,
      "retries": 0,
      "retries_failed": 0
    }
  }
}

Metrics in Prometheus format

Query internal metrics in Prometheus Text 0.0.4 format:

$ curl -s http://127.0.0.1:2020/api/v1/metrics/prometheus

this time the same metrics will be in Prometheus format instead of JSON:

fluentbit_input_records_total{name="cpu.0"} 57 1509150350542
fluentbit_input_bytes_total{name="cpu.0"} 18069 1509150350542
fluentbit_output_proc_records_total{name="stdout.0"} 54 1509150350542
fluentbit_output_proc_bytes_total{name="stdout.0"} 17118 1509150350542
fluentbit_output_errors_total{name="stdout.0"} 0 1509150350542
fluentbit_output_retries_total{name="stdout.0"} 0 1509150350542
fluentbit_output_retries_failed_total{name="stdout.0"} 0 1509150350542

Configuring Aliases

By default configured plugins on runtime get an internal name in the format plugin_name.ID. For monitoring purposes, this can be confusing if many plugins of the same type were configured. To make a distinction each configured input or output section can get an alias that will be used as the parent name for the metric.

The following example set an alias to the INPUT section which is using the CPU input plugin:

[SERVICE]
    HTTP_Server  On
    HTTP_Listen  0.0.0.0
    HTTP_PORT    2020

[INPUT]
    Name  cpu
    Alias server1_cpu

[OUTPUT]
    Name  stdout
    Alias raw_output
    Match *

Now when querying the metrics we get the aliases in place instead of the plugin name:

{
  "input": {
    "server1_cpu": {
      "records": 8,
      "bytes": 2536
    }
  },
  "output": {
    "raw_output": {
      "proc_records": 5,
      "proc_bytes": 1585,
      "errors": 0,
      "retries": 0,
      "retries_failed": 0
    }
  }
}

Grafana Dashboard and Alerts

Fluent Bit's exposed prometheus style metrics can be leveraged to create dashboards and alerts.

The provided example dashboard is heavily inspired by Banzai Cloud's logging operator dashboard but with a few key differences such as the use of the instance label (see why here), stacked graphs and a focus on Fluent Bit metrics.

Alerts

Sample alerts are available here.

Health Check for Fluent Bit

Fluent bit now supports four new configs to set up the health check.

Note: Not every error log means an error nor be counted, the errors retry failures count only on specific errors which is the example in config table description

So the feature works as: Based on the HC_Period customer setup, if the real error number is over HC_Errors_Count or retry failure is over HC_Retry_Failure_Count, fluent bit will be considered as unhealthy. The health endpoint will return HTTP status 500 and String error. Otherwise it's healthy, will return HTTP status 200 and string ok

The equation is:

health status = (HC_Errors_Count > HC_Errors_Count config value) OR (HC_Retry_Failure_Count > HC_Retry_Failure_Count config value) IN the HC_Period interval

Note: the HC_Errors_Count and HC_Retry_Failure_Count only count for output plugins and count a sum for errors and retry failures from all output plugins which is running.

See the config example:

[SERVICE]
    HTTP_Server  On
    HTTP_Listen  0.0.0.0
    HTTP_PORT    2020
    Health_Check On 
    HC_Errors_Count 5 
    HC_Retry_Failure_Count 5 
    HC_Period 5 

[INPUT]
    Name  cpu

[OUTPUT]
    Name  stdout
    Match *

The command to call health endpoint

$ curl -s http://127.0.0.1:2020/api/v1/health

Based on the fluent bit status, the result will be:

• HTTP status 200 and "ok" in response to healthy status

• HTTP status 500 and "error" in response for unhealthy status

With the example config, the health status is determined by following equation:

Health status = (HC_Errors_Count > 5) OR (HC_Retry_Failure_Count > 5) IN 5 seconds

If (HC_Errors_Count > 5) OR (HC_Retry_Failure_Count > 5) IN 5 seconds is TRUE, then it's unhealthy.

If (HC_Errors_Count > 5) OR (HC_Retry_Failure_Count > 5) IN 5 seconds is FALSE, then it's healthy.

Calyptia Cloud

Calyptia Cloud is a hosted service that allows you to monitor your Fluent Bit agents including data flow, metrics and configurations.

Get Started with Calyptia Cloud

Register your Fluent Bit agent will take less than one minute, steps:

• Go to cloud.calyptia.com and sign-in

• On the left menu click on Settings and generate/copy your API key

In your Fluent Bit configuration file, append the following configuration section:

[CUSTOM]
    name     calyptia
    api_key  <YOUR_API_KEY>

Make sure to replace your API key in the configuration. After a few seconds upon restart your Fluent Bit agent, the Calyptia Cloud Dashboard will list your agent. Metrics will take around 30 seconds to shows up.

Contact Calyptia

If want to get in touch with Calyptia team, just send an email to hello@calyptia.com