Service
The service section of YAML configuration files defines global properties of the Fluent Bit service. The available configuration keys are:
flush
Sets the flush time in seconds.nanoseconds. The engine loop uses a flush timeout to define when to flush the records ingested by input plugins through the defined output plugins.
1
grace
Sets the grace time in seconds as an integer value. The engine loop uses a grace timeout to define the wait time on exit.
5
daemon
Specifies whether Fluent Bit should run as a daemon (background process). Possible values: yes, no, on, and off. Don't enable when using a Systemd-based unit, such as the one provided in Fluent Bit packages.
off
dns.mode
Sets the primary transport layer protocol used by the asynchronous DNS resolver. Can be overridden on a per-plugin basis.
UDP
log_file
Absolute path for an optional log file. By default, all logs are redirected to the standard error interface (stderr).
none
log_level
Sets the logging verbosity level. Possible values: off, error, warn, info, debug, and trace. Values are cumulative. For example, if debug is set, it will include error, warning, info, and debug. The trace mode is only available if Fluent Bit was built with the WITH_TRACE option enabled.
info
plugins_file
Path for a plugins configuration file. This file specifies the paths to external plugins (.so files) that Fluent Bit can load at runtime. Plugins can also be declared directly in the plugins section of YAML configuration files.
none
streams_file
Path for the stream processor configuration file. This file defines the rules and operations for stream processing in Fluent Bit. Stream processor configurations can also be defined directly in the streams section of YAML configuration files.
none
http_server
Enables the built-in HTTP server.
off
http_listen
Sets the listening interface for the HTTP Server when it's enabled.
0.0.0.0
http_port
Sets the TCP port for the HTTP server.
2020
coro_stack_size
Sets the coroutines stack size in bytes. The value must be greater than the page size of the running system. Setting the value too small (for example, 4096) can cause coroutine threads to overrun the stack buffer. For best results, don't change this parameter from its default value.
24576
scheduler.cap
Sets a maximum retry time in seconds.
2000
scheduler.base
Sets the base of exponential backoff.
5
json.convert_nan_to_null
If enabled, NaN is converted to null when Fluent Bit converts msgpack to JSON.
false
json.escape_unicode
Controls how Fluent Bit serializes non‑ASCII / multi‑byte Unicode characters in JSON strings. When enabled, Unicode characters are escaped as \uXXXX sequences (characters outside BMP become surrogate pairs). When disabled, Fluent Bit emits raw UTF‑8 bytes.
true
sp.convert_from_str_to_num
If enabled, the stream processor converts strings that represent numbers to a numeric type.
true
windows.maxstdio
If specified, adjusts the limit of stdio. Only provided for Windows. Values from 512 to 2048 are allowed.
512
Storage configuration
The following storage-related keys can be set as children to the storage key:
storage.path
Sets a location to store streams and chunks of data. If this parameter isn't set, input plugins can't use filesystem buffering.
none
storage.sync
Configures the synchronization mode used to store data in the file system. Using full increases the reliability of the filesystem buffer and ensures that data is guaranteed to be synced to the filesystem even if Fluent Bit crashes. On Linux, full corresponds with the MAP_SYNC option for memory mapped files. Accepted values: normal, full.
normal
storage.checksum
Enables data integrity check when writing and reading data from the filesystem. The storage layer uses the CRC32 algorithm. Accepted values: off or on.
off
storage.max_chunks_up
Sets the number of chunks that can be up in memory for input plugins that use filesystem storage.
128
storage.backlog.mem_limit
Sets the memory allocated for storing buffered data for input plugins that use filesystem storage.
5M
storage.backlog.flush_on_shutdown
If enabled, Fluent Bit attempts to flush all backlog filesystem chunks to their destination during the shutdown process. This can help ensure data delivery before Fluent Bit stops, but can also increase shutdown time. Accepted values: off or on.
off
storage.metrics
If http_server option is enabled in the main service section, this option registers a new endpoint where internal metrics of the storage layer can be consumed. For more details, see Monitoring. Accepted values: off or on.
off
storage.delete_irrecoverable_chunks
If enabled, deletes irrecoverable chunks during runtime and at startup. Accepted values: off or on.
off
storage.keep.rejected
If enabled, the dead letter queue stores failed chunks that can't be delivered. Accepted values: off or on.
off
storage.rejected.path
Sets the subdirectory name under storage.path for storing rejected chunks in the dead letter queue.
rejected
For storage and buffering details, see Buffering and Backpressure.
For scheduler and retry details, see Scheduling and retries.
Configuration example
The following configuration example that defines a service section with hot reloading enabled and a pipeline with a random input and stdout output:
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