Buffering & Storage

The end-goal of Fluent Bit is to collect, parse, filter and ship logs to a central place. In this workflow there are many phases and one of the critical pieces is the ability to do buffering : a mechanism to place processed data into a temporal location until is ready to be shipped.
By default when Fluent Bit process data, it uses Memory as a primary and temporal place to store the record logs, but there are certain scenarios where would be ideal to have a persistent buffering mechanism based in the filesystem to provide aggregation and data safety capabilities.
Starting with Fluent Bit v1.0, we introduced a new storage layer that can either work in memory or in the file system. Input plugins can be configured to use one or the other upon demand at start time.
Configuration
The storage layer configuration takes place in two areas:
Service Section
Input Section
The known Service section configure a global environment for the storage layer, and then in the Input sections defines which mechanism to use.
Service Section Configuration
The Service section refers to the section defined in the main configuration file:
Key
Description
Default
storage.path
Set an optional location in the file system to store streams and chunks of data. If this parameter is not set, Input plugins can only use in-memory buffering.
​
storage.sync
Configure the synchronization mode used to store the data into the file system. It can take the values normal or full.
normal
storage.checksum
Enable the data integrity check when writing and reading data from the filesystem. The storage layer uses the CRC32 algorithm.
Off
storage.backlog.mem_limit
If storage.path is set, Fluent Bit will look for data chunks that were not delivered and are still in the storage layer, these are called backlog data. This option configure a hint of maximum value of memory to use when processing these records.
5M
a Service section will look like this:
[SERVICE]
    flush                     1
    log_Level                 info
    storage.path              /var/log/flb-storage/
    storage.sync              normal
    storage.checksum          off
    storage.backlog.mem_limit 5M
that configuration configure an optional buffering mechanism where it root for data is /var/log/flb-storage/, it will use normal synchronization mode, without checksum and up to a maximum of 5MB of memory when processing backlog data.
Input Section Configuration
Optionally, any Input plugin can configure their storage preference, the following table describe the options available:
Key
Description
Default
storage.type
Specify the buffering mechanism to use. It can be memory or filesystem.
memory
The following example configure a service that offers filesystem buffering capabilities and two Input plugins being the first based in memory and the second with the filesystem:
[SERVICE]
    flush                     1
    log_Level                 info
    storage.path              /var/log/flb-storage/
    storage.sync              normal
    storage.checksum          off
    storage.backlog.mem_limit 5M
​
[INPUT]
    name          cpu
    storage.type  filesystem
​
[INPUT]
    name          mem
    storage.type  memory

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Key	Description	Default
storage.path	Set an optional location in the file system to store streams and chunks of data. If this parameter is not set, Input plugins can only use in-memory buffering.
storage.sync	Configure the synchronization mode used to store the data into the file system. It can take the values normal or full.	normal
storage.checksum	Enable the data integrity check when writing and reading data from the filesystem. The storage layer uses the CRC32 algorithm.	Off
storage.backlog.mem_limit	If storage.path is set, Fluent Bit will look for data chunks that were not delivered and are still in the storage layer, these are called backlog data. This option configure a hint of maximum value of memory to use when processing these records.	5M

Key	Description	Default
storage.type	Specify the buffering mechanism to use. It can be memory or filesystem.	memory