A modern logging solution
Eloquent
Installing Fluent Bit
Depending on your use case, you can install Fluent Bit with a package manager, for example, by issuing the Debian/Ubuntu command:
sudo apt-get install td-agent-bit
or running a Docker image:
docker pull fluent/fluent-bit docker run fluent/fluent-bit
as an example of the simplest case.
Configuration
Now construct a configuration file that will allow you to monitor CPU usage and send the metrics to an Elasticsearch instance on localhost. You can use the same [SERVICE]
section as in Listing 5, setting the flush interval of five seconds and logging the events at the info
level (Listing 6).
Listing 6
Fluent Bit CPU Monitoring
[SERVICE] Flush 5 Log_Level info [INPUT] Name cpu Tag cpu.local [OUTPUT] Name es Match * Host localhost Port 9200 Index cpu_metrics
For [INPUT]
, you simply use cpu
as the name and cpu.local
as the tag, which tells Fluent Bit to collect CPU metrics and tag them with cpu.local
. In the [OUTPUT]
section, instead of just displaying data to stdout
, as in Listing 5, you define Host
and Port
, pointing Fluent Bit to a local Elasticsearch instance listening on port 9200
. The logs are stored in the index called cpu_metrics
. The es
plugin has more options (e.g., Buffer_Size
and Retry_Limit
) that can influence the efficiency of the whole setup.
Elasticsearch is a popular option, but many more are possible. If you use AWS, you might want to use the s3
output plugin,
[OUTPUT] Name s3 Match * bucket my-log-bucket region us-west-1 store_dir /tmp/
to send your logs directly to a Simple Storage Service (S3) bucket.
Input Sources
The primary responsibility of Fluent Bit input plugins is to act as gatekeepers, ushering data into the Fluent Bit system. They determine the source of your data, be it system metrics, files, network traffic, or custom sources. One of Fluent Bit's most versatile plugins is tail
, an input plugin. It's designed to read from the end of files, making it particularly useful for tracking logs. With the following setup, Fluent Bit can monitor an application's logfile:
[INPUT] Name tail Path /var/log/myapp.log
You have already seen the cpu
plugin. Fluent Bit's ability to adapt to various data sources extends farther with plugins such as netif
, which collects network interface metrics, or mem
, which is designed to fetch memory usage statistics.
In a more complex scenario, assume you're running a web server and you want to track both the access logs and error logs. Fluent Bit allows you to use multiple input plugins within the same configuration (Listing 7). The dual configuration ensures that both access and error logs flow into Fluent Bit. The distinct tags nginx.access
and nginx.error
allow for easy differentiation and processing downstream.
Listing 7
Two Input Plugins
[INPUT] Name tail Path /var/log/nginx/access.log Tag nginx.access [INPUT] Name tail Path /var/log/nginx/error.log Tag nginx.error
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