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Monitor data pipelines
Learn how to monitor your Fluent Bit data pipelines

Monitor data pipelines

Fluent Bit includes features for monitoring the internals of your pipeline, in addition to connecting to Prometheus and Grafana, Health checks, and connectors to use external services:

HTTP server

Fluent Bit includes an HTTP server for querying internal information and monitoring metrics of each running plugin.

You can integrate the monitoring interface with Prometheus.

Getting started

To get started, enable the HTTP server from the configuration file. The following configuration instructs Fluent Bit to start an HTTP server on TCP port 2020 and listen on all network interfaces:

[SERVICE]
    HTTP_Server  On
    HTTP_Listen  0.0.0.0
    HTTP_PORT    2020

[INPUT]
    Name cpu

[OUTPUT]
    Name  stdout
    Match *

Apply the configuration file:

bin/fluent-bit -c fluent-bit.conf

Fluent Bit starts and generates output in your terminal:

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

Use curl to gather information about the HTTP server. The following command sends the command output to the jq program, which outputs human-readable JSON data to the terminal.

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"
    ]
  }
}

REST API interface

Fluent Bit exposes the following endpoints for monitoring.

URI Description Data format
/ Fluent Bit build information. JSON
/api/v1/uptime Return uptime information in seconds. JSON
/api/v1/metrics Display internal metrics per loaded plugin. JSON
/api/v1/metrics/prometheus Display internal metrics per loaded plugin in Prometheus Server format. Prometheus Text 0.0.4
/api/v1/storage Get internal metrics of the storage layer / buffered data. This option is enabled only if in the SERVICE section of the property storage.metrics is enabled. JSON
/api/v1/health Display the Fluent Bit health check result. String
/api/v2/metrics Display internal metrics per loaded plugin. cmetrics text format
/api/v2/metrics/prometheus Display internal metrics per loaded plugin ready in Prometheus Server format. Prometheus Text 0.0.4
/api/v2/reload Execute hot reloading or get the status of hot reloading. See the hot-reloading documentation. JSON

v1 metrics

The following descriptions apply to v1 metric endpoints.

/api/v1/metrics/prometheus endpoint

The following descriptions apply to metrics outputted in Prometheus format by the /api/v1/metrics/prometheus endpoint.

The following terms are key to understanding how Fluent Bit processes metrics:

  • Record: a single message collected from a source, such as a single long line in a file.

  • Chunk: log records ingested and stored by Fluent Bit input plugin instances. A batch of records in a chunk are tracked together as a single unit.

    The Fluent Bit engine attempts to fit records into chunks of at most 2 MB, but the size can vary at runtime. Chunks are then sent to an output. An output plugin instance can either successfully send the full chunk to the destination and mark it as successful, or it can fail the chunk entirely if an unrecoverable error is encountered, or it can ask for the chunk to be retried.

Metric name Labels Description Type Unit
fluentbit_input_bytes_total name: the name or alias for the input instance The number of bytes of log records that this input instance has ingested successfully. counter bytes
fluentbit_input_records_total name: the name or alias for the input instance The number of log records this input ingested successfully. counter records
fluentbit_output_dropped_records_total name: the name or alias for the output instance The number of log records dropped by the output. These records hit an unrecoverable error or retries expired for their chunk. counter records
fluentbit_output_errors_total name: the name or alias for the output instance The number of chunks with an error that's either unrecoverable or unable to retry. This metric represents the number of times a chunk failed, and doesn't correspond with the number of error messages visible in the Fluent Bit log output. counter chunks
fluentbit_output_proc_bytes_total name: the name or alias for the output instance The number of bytes of log records that this output instance sent successfully. This metric represents the total byte size of all unique chunks sent by this output. If a record is not sent due to some error, it doesn't count towards this metric. counter bytes
fluentbit_output_proc_records_total name: the name or alias for the output instance The number of log records that this output instance sent successfully. This metric represents the total record count of all unique chunks sent by this output. If a record is not sent successfully, it doesn't count towards this metric. counter records
fluentbit_output_retried_records_total name: the name or alias for the output instance The number of log records that experienced a retry. This metric is calculated at the chunk level, the count increased when an entire chunk is marked for retry. An output plugin might perform multiple actions that generate many error messages when uploading a single chunk. counter records
fluentbit_output_retries_failed_total name: the name or alias for the output instance The number of times that retries expired for a chunk. Each plugin configures a Retry_Limit, which applies to chunks. When the Retry_Limit is exceeded, the chunk is discarded and this metric is incremented. counter chunks
fluentbit_output_retries_total name: the name or alias for the output instance The number of times this output instance requested a retry for a chunk. counter chunks
fluentbit_uptime The number of seconds that Fluent Bit has been running. counter seconds
process_start_time_seconds The Unix Epoch timestamp for when Fluent Bit started. gauge seconds

/api/v1/storage endpoint

The following descriptions apply to metrics outputted in JSON format by the /api/v1/storage endpoint.

Metric Key Description Unit
chunks.total_chunks The total number of chunks of records that Fluent Bit is currently buffering. chunks
chunks.mem_chunks The total number of chunks that are currently buffered in memory. Chunks can be both in memory and on the file system at the same time. chunks
chunks.fs_chunks The total number of chunks saved to the filesystem. chunks
chunks.fs_chunks_up The count of chunks that are both in file system and in memory. chunks
chunks.fs_chunks_down The count of chunks that are only in the file system. chunks
input_chunks.{plugin name}.status.overlimit Indicates whether the input instance exceeded its configured Mem_Buf_Limit. boolean
input_chunks.{plugin name}.status.mem_size The size of memory that this input is consuming to buffer logs in chunks. bytes
input_chunks.{plugin name}.status.mem_limit The buffer memory limit (Mem_Buf_Limit) that applies to this input plugin. bytes
input_chunks.{plugin name}.chunks.total The current total number of chunks owned by this input instance. chunks
input_chunks.{plugin name}.chunks.up The current number of chunks that are in memory for this input. If file system storage is enabled, chunks that are "up" are also stored in the filesystem layer. chunks
input_chunks.{plugin name}.chunks.down The current number of chunks that are "down" in the filesystem for this input. chunks
input_chunks.{plugin name}.chunks.busy Chunks are that are being processed or sent by outputs and are not eligible to have new data appended. chunks
input_chunks.{plugin name}.chunks.busy_size The sum of the byte size of each chunk which is currently marked as busy. bytes

v2 metrics

The following descriptions apply to v2 metric endpoints.

/api/v2/metrics/prometheus or /api/v2/metrics endpoint

The following descriptions apply to metrics outputted in Prometheus format by the /api/v2/metrics/prometheus or /api/v2/metrics endpoints.

The following terms are key to understanding how Fluent Bit processes metrics:

  • Record: a single message collected from a source, such as a single long line in a file.

  • Chunk: log records ingested and stored by Fluent Bit input plugin instances. A batch of records in a chunk are tracked together as a single unit.

    The Fluent Bit engine attempts to fit records into chunks of at most 2 MB, but the size can vary at runtime. Chunks are then sent to an output. An output plugin instance can either successfully send the full chunk to the destination and mark it as successful, or it can fail the chunk entirely if an unrecoverable error is encountered, or it can ask for the chunk to be retried.

Metric Name Labels Description Type Unit
fluentbit_input_bytes_total name: the name or alias for the input instance The number of bytes of log records that this input instance has ingested successfully. counter bytes
fluentbit_input_records_total name: the name or alias for the input instance The number of log records this input ingested successfully. counter records
fluentbit_filter_bytes_total name: the name or alias for the filter instance The number of bytes of log records that this filter instance has ingested successfully. counter bytes
fluentbit_filter_records_total name: the name or alias for the filter instance The number of log records this filter has ingested successfully. counter records
fluentbit_filter_added_records_total name: the name or alias for the filter instance The number of log records added by the filter into the data pipeline. counter records
fluentbit_filter_drop_records_total name: the name or alias for the filter instance The number of log records dropped by the filter and removed from the data pipeline. counter records
fluentbit_output_dropped_records_total name: the name or alias for the output instance The number of log records dropped by the output. These records hit an unrecoverable error or retries expired for their chunk. counter records
fluentbit_output_errors_total name: the name or alias for the output instance The number of chunks with an error that's either unrecoverable or unable to retry. This metric represents the number of times a chunk failed, and doesn't correspond with the number of error messages visible in the Fluent Bit log output. counter chunks
fluentbit_output_proc_bytes_total name: the name or alias for the output instance The number of bytes of log records that this output instance sent successfully. This metric represents the total byte size of all unique chunks sent by this output. If a record is not sent due to some error, it doesn't count towards this metric. counter bytes
fluentbit_output_proc_records_total name: the name or alias for the output instance The number of log records that this output instance sent successfully. This metric represents the total record count of all unique chunks sent by this output. If a record is not sent successfully, it doesn't count towards this metric. counter records
fluentbit_output_retried_records_total name: the name or alias for the output instance The number of log records that experienced a retry. This metric is calculated at the chunk level, the count increased when an entire chunk is marked for retry. An output plugin might perform multiple actions that generate many error messages when uploading a single chunk. counter records
fluentbit_output_retries_failed_total name: the name or alias for the output instance The number of times that retries expired for a chunk. Each plugin configures a Retry_Limit, which applies to chunks. When the Retry_Limit is exceeded, the chunk is discarded and this metric is incremented. counter chunks
fluentbit_output_retries_total name: the name or alias for the output instance The number of times this output instance requested a retry for a chunk. counter chunks
fluentbit_uptime hostname: the hostname on running Fluent Bit The number of seconds that Fluent Bit has been running. counter seconds
fluentbit_process_start_time_seconds hostname: the hostname on running Fluent Bit The Unix Epoch time stamp for when Fluent Bit started. gauge seconds
fluentbit_build_info hostname: the hostname, version: the version of Fluent Bit, os: OS type Build version information. The returned value is originated from initializing the Unix Epoch time stamp of configuration context. gauge seconds
fluentbit_hot_reloaded_times hostname: the hostname on running Fluent Bit Collect the count of hot reloaded times. gauge seconds

Storage layer

The following are detailed descriptions for the metrics collected by the storage layer.

Metric Name Labels Description Type Unit
fluentbit_input_chunks.storage_chunks None The total number of chunks of records that Fluent Bit is currently buffering. gauge chunks
fluentbit_storage_mem_chunk None The total number of chunks that are currently buffered in memory. Chunks can be both in memory and on the file system at the same time. gauge chunks
fluentbit_storage_fs_chunks None The total number of chunks saved to the file system. gauge chunks
fluentbit_storage_fs_chunks_up None The count of chunks that are both in file system and in memory. gauge chunks
fluentbit_storage_fs_chunks_down None The count of chunks that are only in the file system. gauge chunks
fluentbit_storage_fs_chunks_busy None The total number of chunks are in a busy state. gauge chunks
fluentbit_storage_fs_chunks_busy_bytes None The total bytes of chunks are in a busy state. gauge bytes
fluentbit_input_storage_overlimit name: the name or alias for the input instance Indicates whether the input instance exceeded its configured Mem_Buf_Limit. gauge boolean
fluentbit_input_storage_memory_bytes name: the name or alias for the input instance The size of memory that this input is consuming to buffer logs in chunks. gauge bytes
fluentbit_input_storage_chunks name: the name or alias for the input instance The current total number of chunks owned by this input instance. gauge chunks
fluentbit_input_storage_chunks_up name: the name or alias for the input instance The current number of chunks that are in memory for this input. If file system storage is enabled, chunks that are "up" are also stored in the filesystem layer. gauge chunks
fluentbit_input_storage_chunks_down name: the name or alias for the input instance The current number of chunks that are "down" in the filesystem for this input. gauge chunks
fluentbit_input_storage_chunks_busy name: the name or alias for the input instance Chunks are that are being processed or sent by outputs and are not eligible to have new data appended. gauge chunks
fluentbit_input_storage_chunks_busy_bytes name: the name or alias for the input instance The sum of the byte size of each chunk which is currently marked as busy. gauge bytes
fluentbit_output_upstream_total_connections name: the name or alias for the output instance The sum of the connection count of each output plugins. gauge bytes
fluentbit_output_upstream_busy_connections name: the name or alias for the output instance The sum of the connection count in a busy state of each output plugins. gauge bytes

Uptime example

Query the service uptime with the following command:

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

The command prints 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 example

Query internal metrics in JSON format with the following command:

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

The command prints 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
    }
  }
}

Query 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 command returns the same metrics 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

Configure 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 sets an alias to the INPUT section of the configuration file, 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 *

When querying the related metrics, the aliases are returned 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

You can create Grafana dashboards and alerts using Fluent Bit's exposed Prometheus style metrics.

The provided example dashboard is heavily inspired by Banzai Cloud's logging operator dashboard with a few key differences, such as the use of the instance label, stacked graphs, and a focus on Fluent Bit metrics. See this blog post for more information.

dashboard

Alerts

Sample alerts are available here.

Health Check for Fluent Bit

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

Configuration name Description Default
Health_Check enable Health check feature Off
HC_Errors_Count the error count to meet the unhealthy requirement, this is a sum for all output plugins in a defined HC_Period, example for output error: [2022/02/16 10:44:10] [ warn] [engine] failed to flush chunk '1-1645008245.491540684.flb', retry in 7 seconds: task_id=0, input=forward.1 > output=cloudwatch_logs.3 (out_id=3) 5
HC_Retry_Failure_Count the retry failure count to meet the unhealthy requirement, this is a sum for all output plugins in a defined HC_Period, example for retry failure: [2022/02/16 20:11:36] [ warn] [engine] chunk '1-1645042288.260516436.flb' cannot be retried: task_id=0, input=tcp.3 > output=cloudwatch_logs.1 5
HC_Period The time period by second to count the error and retry failure data point 60

Not every error log means an error to be counted. The error retry failures count only on specific errors, which is the example in configuration table description.

Based on the HC_Period setting, if the real error number is over HC_Errors_Count, or retry failure is over HC_Retry_Failure_Count, Fluent Bit is considered unhealthy. The health endpoint returns an HTTP status 500 and an error message. Otherwise, the endpoint returns HTTP status 200 and an ok message.

The equation to calculate this behavior 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

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 running output plugins.

The following configuration file example shows how to define these settings:

[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 *

Use the following command to call the health endpoint:

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

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

Health status = (HC_Errors_Count > 5) OR (HC_Retry_Failure_Count > 5) IN 5 seconds
  • If this equation evaluates to TRUE, then Fluent Bit is unhealthy.
  • If this equation evaluates to FALSE, then Fluent Bit is healthy.

Telemetry Pipeline

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