coredns/plugin/ready

ready

Name

ready - enables a readiness check HTTP endpoint.

Description

By enabling ready an HTTP endpoint on port 8181 will return 200 OK, when all plugins that are able to signal readiness have done so. If some are not ready yet the endpoint will return a 503 with the body containing the list of plugins that are not ready.

Each Server Block that enables the ready plugin will have the plugins in that server block report readiness into the /ready endpoint that runs on the same port. This also means that the same plugin with different configurations (in potentially different Server Blocks) will have their readiness reported as the union of their respective readinesses.

Syntax

ready [ADDRESS] {
    monitor until-ready|continuously
}

ready optionally takes an address; the default is :8181. The path is fixed to /ready. The readiness endpoint returns a 200 response code and the word "OK" when this server is ready. It returns a 503 otherwise and the list of plugins that are not ready. By default, once a plugin has signaled it is ready it will not be queried again.

The ready directive can include an optional monitor parameter, defaulting to until-ready. The following values are supported:

• until-ready - once a plugin signals it is ready, it will not be checked again. This mode assumes stability after the initial readiness confirmation.
• continuously - in this mode, plugins are continuously monitored for readiness. This means a plugin may transition between ready and not ready states, providing real-time status updates.

Plugins

Any plugin wanting to signal readiness will need to implement the ready.Readiness interface by implementing a method Ready() bool that returns true when the plugin is ready and false otherwise.

Examples

Let ready report readiness for both the . and example.org servers (assuming the whois plugin also exports readiness):

. {
    ready
    erratic
}

example.org {
    ready
    whoami
}

Run ready on a different port.

. {
    ready localhost:8091
}