rate-initial-burst available in httpd 2.4.24 and later.
Rate limiting proxied content does not work correctly up to httpd 2.4.33.
Provides a filter named RATE_LIMIT to limit client bandwidth.
The throttling is applied to each HTTP response while it is transferred to the client,
and not aggregated at IP/client level.
The connection speed to be simulated is specified, in KiB/s, using the environment
variable rate-limit.
Optionally, an initial amount of burst data, in KiB, may be
configured to be passed at full speed before throttling to the
specified rate limit. This value is optional, and is set using
the environment variable rate-initial-burst.
rate-limit causes integer overflow, the rate-limited will be disabled.
If the value specified for rate-limit-burst causes integer overflow, the burst will be disabled.