Add exponential backoff to healthcheck (#3643)

Move exponential backoff initialization to Start()

Signed-off-by: RickyRajinder <singh.sangh@gmail.com>

Move comment

Increase max interval and update README

Remove trailing whitespace

Change Start() param name back to interval

1 files changed, 4 insertions, 2 deletions

diff --git a/plugin/forward/README.md b/plugin/forward/README.md
index cc1845377..b4307d8dd 100644
--- a/plugin/forward/README.md
+++ b/plugin/forward/README.md
@@ -9,8 +9,10 @@
 The *forward* plugin re-uses already opened sockets to the upstreams. It supports UDP, TCP and
 DNS-over-TLS and uses in band health checking.
 
-When it detects an error a health check is performed. This checks runs in a loop, every *0.5s*, for
-as long as the upstream reports unhealthy. Once healthy we stop health checking (until the next
+When it detects an error a health check is performed. This checks runs in a loop,
+starting with a *0.5s* interval and exponentially backing off with randomized intervals
+up to *60s* for as long as the upstream reports unhealthy. The exponential backoff
+will reset to *0.5s* after 15 minutes. Once healthy we stop health checking (until the next
 error). The health checks use a recursive DNS query (`. IN NS`) to get upstream health. Any response
 that is not a network error (REFUSED, NOTIMPL, SERVFAIL, etc) is taken as a healthy upstream. The
 health check uses the same protocol as specified in **TO**. If `max_fails` is set to 0, no checking