Balancer option

[X-Oracle]

I want a balancer option which works like this :
First we make an ordered list,

1.the balancer should pick the first,
2.If first one faild, then goes to second,
3.if second failed then goes to third,
4. ...,
5.If all fails then goes to fallback.

OR

Use something (like observatory or burst observatory) to ping all of it and connects to first one in order that has the ping.

Its mechanism is similar to leastping and leastload. But gives more control to user for what should connect it fails.

[firengate]

This option would be awesome!

[majorcheng]

同遇到这个需求，其实要的就是“First Available”（首个可用/主备模式）， 方便比如优先走CF， cf挂了的话（最近经常）走直通。
改也简单， pick的时候总是返回第一个就完事了（可以优化一下for循环第一个符合就跳出，懒得改太多了）。顺手把tag的排序也给干了，不知道之前为啥要排序还不如不排序按照config里面的顺序更友好

diff --git a/app/proxyman/outbound/outbound.go b/app/proxyman/outbound/outbound.go
index 244fcffe..df0c9be6 100644
--- a/app/proxyman/outbound/outbound.go
+++ b/app/proxyman/outbound/outbound.go
@@ -2,7 +2,7 @@ package outbound
 
 import (
        "context"
-       "sort"
+       //"sort"
        "strings"
        "sync"
 
@@ -182,7 +182,7 @@ func (m *Manager) Select(selectors []string) []string {
                }
        }
 
-       sort.Strings(tags)
+       //sort.Strings(tags)
        m.tagsCache.Store(key, tags)
 
        return tags
diff --git a/app/router/balancing.go b/app/router/balancing.go
index 5f8cb1c2..af264c6c 100644
--- a/app/router/balancing.go
+++ b/app/router/balancing.go
@@ -75,10 +75,11 @@ func (s *RoundRobinStrategy) PickOutbound(tags []string) string {
                return ""
        }
 
-       s.mu.Lock()
-       defer s.mu.Unlock()
-       tag := tags[s.index%n]
-       s.index = (s.index + 1) % n
+       //s.mu.Lock()
+       //defer s.mu.Unlock()
+       //tag := tags[s.index%n]
+       //s.index = (s.index + 1) % n
+    tag := tags[0]
        return tag
 }