got 502 error when accessing http sites

[escapezn]

1. What version of Caddy are you using (caddy -version)?

Caddy 0.11.0 (non-commercial use only)

2. What are you trying to do?

Use forwardproxy plugin to serve as a forward proxy.

3. What is your entire Caddyfile?

*.* {
 timeouts none
 tls *@*
 header / Strict-Transport-Security "max-age=31536000;"
# ...
 gzip
# ...
 proxy /ws 127.0.0.1:9613 {
  websocket
  header_upstream -Origin
 }
 forwardproxy {
  basicauth user passwd
  hide_ip
  hide_via
#  probe_resistance secretlink.localhost
  response_timeout 10
  dial_timeout     10
 }
}

4. How did you run Caddy (give the full command and describe the execution environment)?

./caddy --conf=/usr/local/caddy/Caddyfile -agree
centos 6.9 x64

5. Please paste any relevant HTTP request(s) here.

6. What did you expect to see?

7. What did you see instead (give full error messages and/or log)?

When I access https sites over the https proxy, it works fine. But for http site it shows 502 Bad Gateway in broswer.
Caddy's log here
01/Jul/2018:08:40:45 -0400 [ERROR 502 /favicon.ico] dial failed: Lookup of fai led: lookup : no such host 01/Jul/2018:08:40:46 -0400 [ERROR 502 /] dial failed: Lookup of failed: lookup : no such host 01/Jul/2018:08:40:51 -0400 [ERROR 502 /] dial failed: Lookup of failed: lookup : no such host 01/Jul/2018:08:40:53 -0400 [ERROR 502 /image] dial failed: Lookup of failed: l ookup : no such host 01/Jul/2018:08:40:54 -0400 [ERROR 502 /image] dial failed: Lookup of failed: l ookup : no such host 01/Jul/2018:08:40:54 -0400 [ERROR 502 /image] dial failed: Lookup of failed: l ookup : no such host 01/Jul/2018:08:40:54 -0400 [ERROR 502 /image] dial failed: Lookup of failed: l ookup : no such host 01/Jul/2018:08:40:54 -0400 [ERROR 502 /image] dial failed: Lookup of failed: l ookup : no such host 01/Jul/2018:08:40:54 -0400 [ERROR 502 /image] dial failed: Lookup of failed: l ookup : no such host 01/Jul/2018:08:40:54 -0400 [ERROR 502 /image] dial failed: Lookup of failed: l ookup : no such host
What surprised me most is that I have tested an exactly same caddyfile(except domain) on another server , also with caddy 0.11.0, and nothing like this happend.

8. How can someone who is starting from scratch reproduce the bug as minimally as possible?

[sergeyfrolov]

Does that happen for all HTTP hosts or for particular few?
Evidently, it fails to DNS resolve the host you're trying to access. You seem to have redacted the host away, so I can't tell why this would happen.
You can try to run host your-http-host.com or dig your-http-host.com on the server with forwardproxy, and see if it's resolvable and if the resolved address is correct. Perhaps, it gets DNS poisoned?

[escapezn]

Yes, as long as http sites it reports 502.
My host website on this server is absolutely accessible.
With your direction, I typed ./caddy -host my.host
It returned

Activating privacy features... done.
https://my.host
http://my.host

Looks good, right? Then I visit a http site, for example http://earthquake.usgs.gov/ over forwardproxy, the log are

02/Jul/2018:21:17:20 -0400 [ERROR 502 /] dial failed: Lookup of failed: lookup : no such host
02/Jul/2018:21:17:20 -0400 [ERROR 502 /favicon.ico] dial failed: Lookup of failed: lookup : no such host

[escapezn]

It seems like forwardproxy regards the http site I visit is under my domain, http://a.com/b.html as my.host/b.html

[sergeyfrolov]

Bug is fixed (updated version is available on caddyserver.com)