reverseproxy: Remove circuitbreaker module (see #3331)

Moving to https://github.com/caddyserver/circuitbreaker

Nobody was using it anyway -- it works well, but something got fumbled
in a refactoring *months* ago. Turns out that we forgot the interface
guards AND botched a method name (my bad) - Ok() should have been OK().
So it would always have thrown a runtime panic if it tried to be loaded.
The module itself works well, but obviously nobody used it because
nobody reported the error. Fixing this while we move it to the new repo.

Removing this removes the last Bazaar/Launchpad dependency (I think).

go.mod

@@ -24,7 +24,6 @@ require (
 	github.com/smallstep/certificates v0.14.2
 	github.com/smallstep/cli v0.14.2
 	github.com/smallstep/truststore v0.9.5
-	github.com/vulcand/oxy v1.1.0
 	github.com/yuin/goldmark v1.1.28
 	github.com/yuin/goldmark-highlighting v0.0.0-20200307114337-60d527fdb691
 	go.uber.org/zap v1.14.1

go.sum

@@ -161,8 +161,6 @@ github.com/chzyer/test v0.0.0-20180213035817-a1ea475d72b1/go.mod h1:Q3SI9o4m/ZMn
 github.com/client9/misspell v0.3.4/go.mod h1:qj6jICC3Q7zFZvVWo7KLAzC3yx5G7kyvSDkc90ppPyw=
 github.com/cloudflare/cloudflare-go v0.10.2 h1:VBodKICVPnwmDxstcW3biKcDSpFIfS/RELUXsZSBYK4=
 github.com/cloudflare/cloudflare-go v0.10.2/go.mod h1:qhVI5MKwBGhdNU89ZRz2plgYutcJ5PCekLxXn56w6SY=
-github.com/codahale/hdrhistogram v0.0.0-20161010025455-3a0bb77429bd h1:qMd81Ts1T2OTKmB4acZcyKaMtRnY5Y44NuXGX2GFJ1w=
-github.com/codahale/hdrhistogram v0.0.0-20161010025455-3a0bb77429bd/go.mod h1:sE/e/2PUdi/liOCUjSTXgM1o87ZssimdTWN964YiIeI=
 github.com/codegangsta/cli v1.20.0/go.mod h1:/qJNoX69yVSKu5o4jLyXAENLRyk1uhi7zkbQ3slBdOA=
 github.com/coreos/bbolt v1.3.2/go.mod h1:iRUV2dpdMOn7Bo10OQBFzIJO9kkE559Wcmn+qkEiiKk=
 github.com/coreos/bbolt v1.3.3/go.mod h1:iRUV2dpdMOn7Bo10OQBFzIJO9kkE559Wcmn+qkEiiKk=
@@ -375,10 +373,8 @@ github.com/gorilla/mux v1.7.3/go.mod h1:1lud6UwP+6orDFRuTfBEV8e9/aOM/c4fVVCaMa2z
 github.com/gorilla/securecookie v1.1.1/go.mod h1:ra0sb63/xPlUeL+yeDciTfxMRAA+MP+HVt/4epWDjd4=
 github.com/gorilla/websocket v1.4.0/go.mod h1:E7qHFY5m1UJ88s3WnNqhKjPHQ0heANvMoAMk2YaljkQ=
 github.com/gorilla/websocket v1.4.1/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=
-github.com/gorilla/websocket v1.4.2/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=
 github.com/gostaticanalysis/analysisutil v0.0.0-20190318220348-4088753ea4d3/go.mod h1:eEOZF4jCKGi+aprrirO9e7WKB3beBRtWgqGunKl6pKE=
 github.com/gostaticanalysis/analysisutil v0.0.3/go.mod h1:eEOZF4jCKGi+aprrirO9e7WKB3beBRtWgqGunKl6pKE=
-github.com/gravitational/trace v0.0.0-20190726142706-a535a178675f/go.mod h1:RvdOUHE4SHqR3oXlFFKnGzms8a5dugHygGw1bqDstYI=
 github.com/gregjones/httpcache v0.0.0-20180305231024-9cad4c3443a7/go.mod h1:FecbI9+v66THATjSRHfNgh1IVFe/9kFxbXtjV0ctIMA=
 github.com/grpc-ecosystem/go-grpc-middleware v1.0.0/go.mod h1:FiyG127CGDf3tlThmgyCl78X/SZQqEOJBCDaAfeWzPs=
 github.com/grpc-ecosystem/go-grpc-middleware v1.1.0/go.mod h1:f5nM7jw/oeRSadq3xCzHAvxcr8HZnzsqU6ILg/0NiiE=
@@ -477,11 +473,6 @@ github.com/lunixbochs/vtclean v1.0.0/go.mod h1:pHhQNgMf3btfWnGBVipUOjRYhoOsdGqdm
 github.com/magiconair/properties v1.7.6/go.mod h1:PppfXfuXeibc/6YijjN8zIbojt8czPbwD3XqdrwzmxQ=
 github.com/magiconair/properties v1.8.0/go.mod h1:PppfXfuXeibc/6YijjN8zIbojt8czPbwD3XqdrwzmxQ=
 github.com/magiconair/properties v1.8.1/go.mod h1:PppfXfuXeibc/6YijjN8zIbojt8czPbwD3XqdrwzmxQ=
-github.com/mailgun/minheap v0.0.0-20170619185613-3dbe6c6bf55f/go.mod h1:V3EvCedtJTvUYzJF2GZMRB0JMlai+6cBu3VCTQz33GQ=
-github.com/mailgun/multibuf v0.0.0-20150714184110-565402cd71fb/go.mod h1:E0vRBBIQUHcRtmL/oR6w/jehh4FJqJFxe86gBnw9gXc=
-github.com/mailgun/timetools v0.0.0-20141028012446-7e6055773c51 h1:Kg/NPZLLC3aAFr1YToMs98dbCdhootQ1hZIvZU28hAQ=
-github.com/mailgun/timetools v0.0.0-20141028012446-7e6055773c51/go.mod h1:RYmqHbhWwIz3z9eVmQ2rx82rulEMG0t+Q1bzfc9DYN4=
-github.com/mailgun/ttlmap v0.0.0-20170619185759-c1c17f74874f/go.mod h1:8heskWJ5c0v5J9WH89ADhyal1DOZcayll8fSbhB+/9A=
 github.com/mailru/easyjson v0.0.0-20190312143242-1de009706dbe/go.mod h1:C1wdFJiN94OJF2b5HbByQZoLdCWB1Yqtg26g4irojpc=
 github.com/manifoldco/promptui v0.3.1/go.mod h1:zoCNXiJnyM03LlBgTsWv8mq28s7aTC71UgKasqRJHww=
 github.com/manifoldco/promptui v0.7.0 h1:3l11YT8tm9MnwGFQ4kETwkzpAwY2Jt9lCrumCUW4+z4=
@@ -774,9 +765,6 @@ github.com/valyala/quicktemplate v1.2.0/go.mod h1:EH+4AkTd43SvgIbQHYu59/cJyxDoOV
 github.com/valyala/tcplisten v0.0.0-20161114210144-ceec8f93295a/go.mod h1:v3UYOV9WzVtRmSR+PDvWpU/qWl4Wa5LApYYX4ZtKbio=
 github.com/viant/assertly v0.4.8/go.mod h1:aGifi++jvCrUaklKEKT0BU95igDNaqkvz+49uaYMPRU=
 github.com/viant/toolbox v0.24.0/go.mod h1:OxMCG57V0PXuIP2HNQrtJf2CjqdmbrOx5EkMILuUhzM=
-github.com/vulcand/oxy v1.1.0 h1:DbBijGo1+6cFqR9jarkMxasdj0lgWwrrFtue6ijek4Q=
-github.com/vulcand/oxy v1.1.0/go.mod h1:ADiMYHi8gkGl2987yQIzDRoXZilANF4WtKaQ92OppKY=
-github.com/vulcand/predicate v1.1.0/go.mod h1:mlccC5IRBoc2cIFmCB8ZM62I3VDb6p2GXESMHa3CnZg=
 github.com/vultr/govultr v0.1.4 h1:UnNMixYFVO0p80itc8PcweoVENyo1PasfvwKhoasR9U=
 github.com/vultr/govultr v0.1.4/go.mod h1:9H008Uxr/C4vFNGLqKx232C206GL0PBHzOP0809bGNA=
 github.com/weppos/publicsuffix-go v0.4.0/go.mod h1:z3LCPQ38eedDQSwmsSRW4Y7t2L8Ln16JPQ02lHAdn5k=
@@ -1203,7 +1191,6 @@ howett.net/plist v0.0.0-20181124034731-591f970eefbb h1:jhnBjNi9UFpfpl8YZhA9CrOqp
 howett.net/plist v0.0.0-20181124034731-591f970eefbb/go.mod h1:vMygbs4qMhSZSc4lCUl2OEE+rDiIIJAIdR4m7MiMcm0=
 howett.net/plist v0.0.0-20200225050739-77e249a2e2ba h1:HiEs/6jQFMHpFqsdPBAk3ieVcsSS8IV+D93f43UuDPo=
 howett.net/plist v0.0.0-20200225050739-77e249a2e2ba/go.mod h1:vMygbs4qMhSZSc4lCUl2OEE+rDiIIJAIdR4m7MiMcm0=
-launchpad.net/gocheck v0.0.0-20140225173054-000000000087/go.mod h1:hj7XX3B/0A+80Vse0e+BUHsHMTEhd0O4cpUHr/e/BUM=
 mvdan.cc/interfacer v0.0.0-20180901003855-c20040233aed/go.mod h1:Xkxe497xwlCKkIaQYRfC7CSLworTXY9RMqwhhCm+8Nc=
 mvdan.cc/lint v0.0.0-20170908181259-adc824a0674b/go.mod h1:2odslEg/xrtNQqCYg2/jCoyKnw3vv5biOc3JnIcYfL4=
 mvdan.cc/unparam v0.0.0-20190209190245-fbb59629db34/go.mod h1:H6SUd1XjIs+qQCyskXg5OFSrilMRUkD8ePJpHKDPaeY=

modules/caddyhttp/reverseproxy/healthchecks.go

@@ -113,7 +113,8 @@ type PassiveHealthChecks struct {
 
 // CircuitBreaker is a type that can act as an early-warning
 // system for the health checker when backends are getting
-// overloaded.
+// overloaded. This interface is still experimental and is
+// subject to change.
 type CircuitBreaker interface {
 	OK() bool
 	RecordMetric(statusCode int, latency time.Duration)