Tail
The tail input plugin allows to monitor one or several text files. It has a similar behavior like tail -f
shell command.
The plugin reads every matched file in the Path
pattern and for every new line found (separated by a \n
), it generates a new record. Optionally a database file can be used so the plugin can have a history of tracked files and a state of offsets, this is very useful to resume a state if the service is restarted.
Configuration Parameters
The plugin supports the following configuration parameters:
Note that if the database parameter DB
is not specified, by default the plugin will start reading each target file from the beginning. This also might cause some unwanted behaviour, for example when a line is bigger that Buffer_Chunk_Size
and Skip_Long_Lines
is not turned on, the file will be read from the beginning each Refresh_Interval
until the file is rotated.
Multiline Configuration Parameters
Additionally the following options exists to configure the handling of multi-lines files:
Docker Mode Configuration Parameters
Docker mode exists to recombine JSON log lines split by the Docker daemon due to its line length limit. To use this feature, configure the tail plugin with the corresponding parser and then enable Docker mode:
Getting Started
In order to tail text or log files, you can run the plugin from the command line or through the configuration file:
Command Line
From the command line you can let Fluent Bit parse text files with the following options:
Configuration File
In your main configuration file append the following Input & Output sections. An example visualization can be found here
Multi-line example
When using multi-line configuration you need to first specify Multiline On
in the configuration and use the Parser_Firstline
and additional parser parameters Parser_N
if needed. If we are trying to read the following Java Stacktrace as a single event
We need to specify a Parser_Firstline
parameter that matches the first line of a multi-line event. Once a match is made Fluent Bit will read all future lines until another match with Parser_Firstline
is made .
In the case above we can use the following parser, that extracts the Time as time
and the remaining portion of the multiline as log
If we want to further parse the entire event we can add additional parsers with Parser_N
where N is an integer. The final Fluent Bit configuration looks like the following:
Our output will be as follows.
Tailing files keeping state
The tail input plugin a feature to save the state of the tracked files, is strongly suggested you enabled this. For this purpose the db property is available, e.g:
When running, the database file /path/to/logs.db will be created, this database is backed by SQLite3 so if you are interested into explore the content, you can open it with the SQLite client tool, e.g:
Make sure to explore when Fluent Bit is not hard working on the database file, otherwise you will see some Error: database is locked messages.
Formatting SQLite
By default SQLite client tool do not format the columns in a human read-way, so to explore in_tail_files table you can create a config file in ~/.sqliterc with the following content:
File Rotation
File rotation is properly handled, including logrotate's copytruncate mode.
Note that the Path
patterns cannot match the rotated files. Otherwise, the rotated file would be read again and lead to duplicate records.
Last updated