haproxy代理mongodb

mongodb集群采用的replication set模式，至少3个节点以上。有个问题，当mongodb主节点down的时候，如何让ceilometer自动连接重新选举出来的主节点？

这里有两种解法，至于采用哪种，看需求。

1、采用vip来定位mongodb主节点

使用keepalived来起vip，这里有两个vip，vrrp_instance VI_1是专门给mongodb用的vip，vrrp_instance VI_2是OpenStack HA用的vip

vrrp script chk_mongo_primary脚本专门来检测该节点是不是mongo master节点，如果是的话权重+2，而且vrrp_instance VI_1的vip是可以抢占的；

当mongodb主节点发生切换，vrrp_instance VI_1的vip也会跟着切换。

keepalived.conf配置文件

! Configuration File for keepalivedvrrp_script chk_haproxy {    script "killall -0 haproxy"    interval 2    weight 2}# Define the script used to check if mongod is runningvrrp_script chk_mongod {    script "killall -0 mongod"    interval 2 # every two seconds    weight 2}# Define the script to see if the local node is the primaryvrrp_script chk_mongo_primary {    script "mongo --eval '(!!db.runCommand("ismaster")["ismaster"])?quit(0):quit(1)'"    interval 2 # every two seconds    weight 2}# Configuation for the virtual interfacevrrp_instance VI_1 {    interface br-ex    state node MASTER        # SLAVE on the other nodes    priority 101             # 100 on other nodes    virtual_router_id 55    authentication {        auth_type PASS        auth_pass secret     # Set this to some secret phrase    }    # The virtual ip address shared between the two nodes    virtual_ipaddress {        172.16.140.251/24    }    # Use the script above to check if we should fail over    track_script {        chk_mongod        chk_mongo_primary    }}vrrp_instance VI_2 {    interface br-ex    virtual_router_id 51    state BACKUP    priority 200# if use it,the openstack api do not response normally#    use_vmac virtualmac#    advert_int 1    dont_track_primary    nopreempt    authentication {    auth_type PASS    auth_pass password    }    virtual_ipaddress {       172.16.140.250/24    }    track_script {      chk_haproxy    }    notify /usr/local/bin/keepalivednotify.sh}

2、使用haproxy的tcp-check来检测

haproyx mongodb配置

listen mongodb_cluster    bind openstack_vip:27017    option tcpka    option tcplog    option tcp-check    # MongoDB Wire Protocol    tcp-check send-binary 3a000000 # Message Length (58)    tcp-check send-binary EEEEEEEE # Request ID (random value)    tcp-check send-binary 00000000 # Response To (nothing)    tcp-check send-binary d4070000 # OpCode (Query)    tcp-check send-binary 00000000 # Query Flags    tcp-check send-binary 61646d696e2e # fullCollectionName (admin.$cmd)    tcp-check send-binary 24636d6400 # continued    tcp-check send-binary 00000000 # NumToSkip    tcp-check send-binary FFFFFFFF # NumToReturn    # Start of Document    tcp-check send-binary 13000000 # Document Length (19)    tcp-check send-binary 10 # Type (Int32)    tcp-check send-binary 69736d617374657200 # ismaster:    tcp-check send-binary 01000000 # Value : 1    tcp-check send-binary 00 # Term        tcp-check expect binary 69736d61737465720001 #ismaster True    server controller1 controller1:27017 check inter 2000 rise 2 fall 3    server controller2 controller2:27017 check inter 2000 rise 2 fall 3

这里有个问题，在haproxy监控页面上看到的非master节点都是down的，因为tcp-check的缘故。

上面send-binary为什么那么写？(用tcpdum抓包出来，拿到wireshark分析)

详情参考这里：https://blog.danman.eu/mongodb-haproxy/

http://serverfault.com/questions/625492/how-to-construct-a-mongodb-health-check-in-haproxy

最后发现mongodb的uri本身支持multi host，形如：mongodb://ceilometer:ceilometer@controller2,controller1,controller3/ceilometer?readPreference=primaryPreferred&replicaSet=rs0

详情参考mongodb官方：https://docs.mongodb.com/manual/reference/connection-string/