proposed stemcell network performance tuning

Amit Kumar Gupta

Hi all,

I'd like to propose tuning a couple kernel parameters related to tcp

# This setting determines the time that must elapse before TCP/IP can
release a closed connection and reuse
# its resources. During this TIME_WAIT state, reopening the connection to
the client costs less than establishing
# a new connection. By reducing the value of this entry, TCP/IP can release
closed connections faster, making more
# resources available for new connections. Adjust this in the presence of
many connections sitting in the
# TIME_WAIT state:

echo 5 > /proc/sys/net/ipv4/tcp_fin_timeout

# This allows reusing sockets in TIME_WAIT state for new connections when
it is safe from protocol viewpoint.
# Default value is 0 (disabled). It is generally a safer alternative to

echo 1 > /proc/sys/net/ipv4/tcp_tw_reuse

Currently, these parameters are set by certain jobs in cf-release,
diego-release, and perhaps others. Any VM needing to establish a high
number of incoming/outgoing tcp connections in a short period of time will
be unable to establish new connections without changing these parameters.

We believe these parameters are safe to change across the board, and will
be generally beneficial. The existing defaults made sense for much older
networks, but can be greatly optimized for modern systems.

Please share with the mailing lists if you have any questions or feedback
about this proposal. If you maintain a bosh release and would like to see
how these changes would affect your release, you can create a job which
simply does the above in its startup scripts, and colocate that job with
all the other jobs in a deployment of your release.


Amit Gupta
Cloud Foundry PM, OSS Release Integration team

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