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Add a ready plugin that allows plugin to signal when they are ready.
Once a plugin is ready it is not queried again.
This uses same mechanism as the health plugin: each plugin needs to
implement an interface.
Implement readines for the *erratic* plugin to aid in testing.
Add README.md and tests moduled after the health plugin; which will be
relegated to just providing process health. In similar vein to health
this is a process wide setting.
With this Corefile:
~~~
. {
erratic
whoami
ready
}
bla {
erratic
whoami
}
~~~
ready will lead to:
~~~ sh
% curl localhost:8181/ready
% dig @localhost -p 1053 mx example.org
% curl localhost:8181/ready
OK%
~~~
Meanwhile CoreDNS logs:
~~~
.:1053
bla.:1053
2019-02-26T20:59:07.137Z [INFO] CoreDNS-1.3.1
2019-02-26T20:59:07.137Z [INFO] linux/amd64, go1.11.4,
CoreDNS-1.3.1
linux/amd64, go1.11.4,
2019-02-26T20:59:11.415Z [INFO] plugin/ready: Still waiting on: "erratic"
2019-02-26T20:59:13.510Z [INFO] plugin/ready: Still waiting on: "erratic"
~~~
*ready* can be used in multiple server blocks and will do the right
thing; query all those plugins from all server blocks for readiness.
This does a similar thing to the prometheus plugin.
Signed-off-by: Miek Gieben <miek@miek.nl>
57 lines
1.3 KiB
Markdown
57 lines
1.3 KiB
Markdown
# ready
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## Name
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*ready* - enables a readiness check HTTP endpoint.
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## Description
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By enabling *ready* an HTTP endpoint on port 8181 will return 200 OK, when all plugins that are able
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to signal readiness have done so. If some are not ready yet the endpoint will return a 503 with the
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body containing the list of plugins that are not ready. Once a plugin has signaled it is ready it
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will not be queried again.
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Each Server Block that enables the *ready* plugin will have the plugins *in that server block*
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report readiness into the /ready endpoint that runs on the same port.
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## Syntax
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~~~
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ready [ADDRESS]
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~~~
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*ready* optionally takes an address; the default is `:8181`. The path is fixed to `/ready`. The
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readiness endpoint returns a 200 response code and the word "OK" when this server is ready. It
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returns a 503 otherwise.
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## Plugins
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Any plugin wanting to signal readiness will need to implement the `ready.Readiness` interface by
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implementing a method `Ready() bool` that returns true when the plugin is ready and false otherwise.
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## Examples
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Let *ready* report readiness for both the `.` and `example.org` servers (assuming the *whois*
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plugin also exports readiness):
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~~~ txt
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. {
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ready
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erratic
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}
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example.org {
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ready
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whoami
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}
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~~~
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Run *ready* on a different port.
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~~~ txt
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. {
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ready localhost:8091
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}
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~~~
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