fluent-plugin-throttle

A sentry plugin to throttle logs. Logs are grouped by a configurable key. When a group exceeds a configuration rate, logs are dropped for this group.

Installation

install with gem or td-agent provided command as:

# for fluentd
$ gem install fluent-plugin-throttle

Usage

<filter **>
  @type throttle
  group_key kubernetes.container_name
  group_bucket_period_s   60
  group_bucket_limit    6000
  group_reset_rate_s     100
</filter>

Configuration

group_key

Default: kubernetes.container_name.

Used to group logs. Groups are rate limited independently.

A dot indicates a key within a sub-object. As an example, in the following log, the group key resolve to "random":

{"level": "error", "msg": "plugin test", "kubernetes": { "container_name": "random" } }

Multiple groups can be specified using the fluentd config array syntax, e.g. kubernetes.container_name,kubernetes.pod_name, in which case each unique pair of key values are rate limited independently.

If the group cannot be resolved, an anonymous (nil) group is used for rate limiting.

group_bucket_period_s

Default: 60 (60 second).

This is the period of of time over which group_bucket_limit applies.

group_bucket_limit

Default: 6000 (logs per group_bucket_period_s).

Maximum number logs allowed per groups over the period of group_bucket_period_s.

This translate to a log rate of group_bucket_limit/group_bucket_period_s. When a group exceeds this rate, logs from this group are dropped.

For example, the default is 6000/60s, making for a rate of 100 logs per seconds.

Note that this is not expressed as a rate directly because there is a difference between the overall rate and the distribution of logs over a period time. For example, a burst of logs in the middle of a minute bucket might not exceed the average rate of the full minute.

Consider 60/60s, 60 logs over a minute, versus 1/1s, 1 log per second. Over a minute, both will emit a maximum of 60 logs. Limiting to a rate of 60 logs per minute. However 60/60s will readily emit 60 logs within the first second then nothing for the remaining 59 seconds. While the 1/1s will only emit the first log of every second.

group_drop_logs

Default: true.

When a group reaches its limit, logs will be dropped from further processing if this value is true (set by default). To prevent the logs from being dropped and only receive a warning message when rate limiting would have occurred, set this value for false. This can be useful to fine-tune your group bucket limits before dropping any logs.

group_reset_rate_s

Default: group_bucket_limit/group_bucket_period_s (logs per group_bucket_period_s). Maximum: group_bucket_limit/group_bucket_period_s.

After a group has exceeded its bucket limit, logs are dropped until the rate per second falls below or equal to group_reset_rate_s.

The default value is group_bucket_limits/group_bucket_period_s. For example for 3600 logs per hour, the reset will defaults to 3600/3600s = 1/s, one log per second.

Taking the example 3600 log/hour with the default reset rate of 1 log/s further:

Let's say we have a period of 10 hours.
During the first hour, 2 logs/s are produced. After 30 minutes, the hourly bucket has reached its limit, and logs are dropped. At this point the rate is still 2 logs/s for the remaining 30 minutes.
Because the last hour finished on 2 logs/s, which is higher that the 1 log/s reset, all logs are still dropped when starting the second hour. The bucket limit is left untouched since nothing is being emitted.
Now, at 2 hours and 30 minutes, the log rate halves to 1 log/s, which is equal to the reset rate. Logs are emitted again, counting toward the bucket limit as normal. Allowing up to 3600 logs for the last 30 minutes of the second hour.

Because this could allow for some instability if the log rate hovers around the group_bucket_limit/group_bucket_period_s rate, it is possible to set a different reset rate.

Note that a value of 0 effectively means the plugin will drops logs forever after a single breach of the limit until the next restart of fluentd.

A value of -1 disables the feature.

group_warning_delay_s

Default: 10 (seconds).

When a group reaches its limit and as long as it is not reset, a warning message with the current log rate of the group is emitted repeatedly. This is the delay between every repetition.

License

Apache License, Version 2.0

rubrikinc/fluent-plugin-throttle