$ go run ok.go

rs=rs0;
0 ~ 0/transcoder-trans-01:27017;
1 ~ 1/transcoder-trans-02:27017;
2 ~ 2/transcoder-trans-03:27017;

$ go run fail.go
rs=rs0;
0 ~ 0/;
1 ~ 0/;
2 ~ 0/;