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109b3f47de
* Update multisocket README.md
I was a bit confused why `multisocket` wasn't working for me, but I eventually found 38c020941b/core/dnsserver/register.go (L308):
```
// create one server by default if no NumSockets specified
numSockets := 1
if group[0].NumSockets > 0 {
numSockets = group[0].NumSockets
}
```
I tried to summarize my understanding in the README
Signed-off-by: Ryan Brewster <rpb@anthropic.com>
* Update plugin/multisocket/README.md
Co-authored-by: Ville Vesilehto <ville@vesilehto.fi>
Signed-off-by: Ryan Brewster <rpb@anthropic.com>
---------
Signed-off-by: Ryan Brewster <rpb@anthropic.com>
Co-authored-by: Ville Vesilehto <ville@vesilehto.fi>
73 lines
2.6 KiB
Markdown
73 lines
2.6 KiB
Markdown
# multisocket
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## Name
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*multisocket* - allows to start multiple servers that will listen on one port.
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## Description
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With *multisocket*, you can define the number of servers that will listen on the same port. The SO_REUSEPORT socket
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option allows to open multiple listening sockets at the same address and port. In this case, kernel distributes incoming
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connections between sockets.
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Enabling this option allows to start multiple servers, which increases the throughput of CoreDNS in environments with a
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large number of CPU cores.
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## Syntax
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~~~
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multisocket [NUM_SOCKETS]
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~~~
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* **NUM_SOCKETS** - the number of servers that will listen on one port. Default value is equal to GOMAXPROCS. Maximum value is 1024.
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## Examples
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Start 5 TCP/UDP servers on the same port.
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~~~ corefile
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. {
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multisocket 5
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forward . /etc/resolv.conf
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}
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~~~
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Do not define `NUM_SOCKETS`, in this case it will take a value equal to GOMAXPROCS.
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~~~ corefile
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. {
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multisocket
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forward . /etc/resolv.conf
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}
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~~~
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## Recommendations
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The tests of the `multisocket` plugin, which were conducted for `NUM_SOCKETS` from 1 to 10, did not reveal any side
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effects or performance degradation.
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This means that the `multisocket` plugin can be used with a default value that is equal to GOMAXPROCS.
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However, to achieve the best results, it is recommended to consider the specific environment and plugins used in
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CoreDNS. To determine the optimal configuration, it is advisable to conduct performance tests with different
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`NUM_SOCKETS`, measuring Queries Per Second (QPS) and system load.
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If conducting such tests is difficult, follow these recommendations:
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1. Determine the maximum CPU consumption of CoreDNS server without `multisocket` plugin. Estimate how much CPU CoreDNS
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actually consumes in specific environment under maximum load.
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2. Align `NUM_SOCKETS` with the estimated CPU usage and CPU limits or system's available resources.
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Examples:
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- If CoreDNS consumes 4 CPUs and 8 CPUs are available, set `NUM_SOCKETS` to 2.
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- If CoreDNS consumes 8 CPUs and 64 CPUs are available, set `NUM_SOCKETS` to 8.
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## Limitations
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The `multisocket` value used for a given listen address is taken from the first server block that binds to that address
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in the Corefile. Subsequent server blocks using the same address will not change it. Different addresses may use
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different values.
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The SO_REUSEPORT socket option is not available for some operating systems. It is available since Linux Kernel 3.9 and
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not available for Windows at all.
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Using this plugin with a system that does not support SO_REUSEPORT will cause an `address already in use` error.
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