Add OnReStartFailed which makes the health plugin stay up if the
Corefile is corrupt and we revert to the previous version.
Also needs a fix for the channel handling
See #2659
Testing it will log the following when restarting with a corrupted
Corefile
~~~
2019-05-04T18:01:59.431Z [INFO] linux/amd64, go1.12.4,
CoreDNS-1.5.0
linux/amd64, go1.12.4,
[INFO] SIGUSR1: Reloading
[INFO] Reloading
[ERROR] Restart failed: Corefile:5 - Error during parsing: Unknown directive 'bdhfhdhj'
[ERROR] SIGUSR1: starting with listener file descriptors: Corefile:5 - Error during parsing: Unknown directive 'bdhfhdhj'
~~~
After which the curl still works.
This also needed a change to reset the channel used for the metrics
go-routine which gets closed on shutdown, otherwise you'll see:
~~~
^C[INFO] SIGINT: Shutting down
panic: close of closed channel
goroutine 90 [running]:
github.com/coredns/coredns/plugin/health.(*health).OnFinalShutdown(0xc000089bc0, 0xc000063d88, 0x4afe6d)
~~~
Signed-off-by: Miek Gieben <miek@miek.nl>
076b8d4fba