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plugin/health: remove ability to poll other plugins (#2547)

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* plugin/health: remove ability to poll other plugins

This mechanism defeats the purpose any plugin (mostly) caching can still
be alive, we can probably forward queries still. Don't poll plugins,
just tell the world we're up and running.

It was only actually used in kubernetes; and there specifically would
mean any network hiccup would NACK the entire server health.

Fixes: #2534

Signed-off-by: Miek Gieben <miek@miek.nl>

* update docs based on feedback

Signed-off-by: Miek Gieben <miek@miek.nl>
This commit is contained in:
Miek Gieben
2019-03-07 22:13:47 +00:00
committed by GitHub
parent db0b16b615
commit c778b3a67c
10 changed files with 18 additions and 173 deletions
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39
plugin/health/README.md
View File

@@ -6,9 +6,8 @@
## Description
By enabling *health* any plugin that implements
[health.Healther interface](https://godoc.org/github.com/coredns/coredns/plugin/health#Healther)
will be queried for it's health. The combined health is exported, by default, on port 8080/health .
Enabled process wide health endpoint. When CoreDNS is up and running this returns a 200 OK http
status code. The health is exported, by default, on port 8080/health .
## Syntax
@@ -17,12 +16,9 @@ health [ADDRESS]
~~~
Optionally takes an address; the default is `:8080`. The health path is fixed to `/health`. The
health endpoint returns a 200 response code and the word "OK" when this server is healthy. It returns
a 503. *health* periodically (1s) polls plugins that exports health information. If any of the
plugins signals that it is unhealthy, the server will go unhealthy too. Each plugin that supports
health checks has a section "Health" in their README.
health endpoint returns a 200 response code and the word "OK" when this server is healthy.
More options can be set with this extended syntax:
An extra option can be set with this extended syntax:
~~~
health [ADDRESS] {
@@ -33,8 +29,8 @@ health [ADDRESS] {
* Where `lameduck` will make the process unhealthy then *wait* for **DURATION** before the process
shuts down.
If you have multiple Server Blocks and need to export health for each of the plugins, you must run
health endpoints on different ports:
If you have multiple Server Blocks, *health* should only be enabled in one of them (as it is process
wide). If you really need multiple endpoints, you must run health endpoints on different ports:
~~~ corefile
com {
@@ -48,21 +44,6 @@ net {
}
~~~
Note that if you format this in one server block you will get an error on startup, that the second
server can't setup the health plugin (on the same port).
~~~ txt
com net {
whoami
erratic
health :8080
}
~~~
## Plugins
Any plugin that implements the Healther interface will be used to report health.
## Metrics
If monitoring is enabled (via the *prometheus* directive) then the following metric is exported:
@@ -96,7 +77,7 @@ Set a lameduck duration of 1 second:
## Bugs
When reloading, the Health handler is stopped before the new server instance is started.
If that new server fails to start, then the initial server instance is still available and DNS queries still served,
but Health handler stays down.
Health will not reply HTTP request until a successful reload or a complete restart of CoreDNS.
When reloading, the health handler is stopped before the new server instance is started. If that
new server fails to start, then the initial server instance is still available and DNS queries still
served, but health handler stays down. Health will not reply HTTP request until a successful reload
or a complete restart of CoreDNS.