How to configure mem_buf_limit for fluentbit

[Tejaswi43]

Bug Report

Describe the bug

Hi team, I have a query regarding how to configure mem_buf_limit to handle backpressure when logstash is not available. The issue was identified when fluetbit stopped with OOM kill issue when container memory limit was set to 30 Mi and logstash was not available for longer time. Increased container memory and verified with different log input rate. Based on the test result observed below behavior when mem_buf_limit is set to 1MB
1log/sec ------> could observe restart after longer time
100log/sec -----> restart didn't happen
200log/sec ------> restart didn't happen

Analysis - If mem_buf_limit is not filled then while harvesting logs fluentbit is consuming more memory. When mem_limit is reached there is not much variation in container memory (mostly 3 to 4 Mi increase after overlimit happens).

Question: It would be great if there is some way to figure out mem_buf_limit value. Thanks in advance!

To Reproduce

• Rubular link if applicable:
• Example log message if applicable:

{"log":"YOUR LOG MESSAGE HERE","stream":"stdout","time":"2018-06-11T14:37:30.681701731Z"}

• Steps to reproduce the problem:

Expected behavior

Screenshots

Your Environment

• Version used:2.1.10
• Configuration:
• Environment name and version (e.g. Kubernetes? What version?):
• Server type and version:
• Operating System and version:
• Filters and plugins:

Additional context

[patrick-stephens]

https://docs.fluentbit.io/manual/administration/buffering-and-storage should cover it.
It does depend specifically on your data rates/size plus actual config (e.g. plugins used/filters/etc.) but hopefully the docs give you that info.

Also you're on an old FB version so should update.