DNS for Service Discovery in HAProxy

blog20190724-01.txt

_service._proto.name. TTL class SRV priority weight port target

blog20190724-02.cfg

resolvers mydns
    nameserver dns1 192.168.50.30:53
    accepted_payload_size 8192 # allow larger DNS payloads

blog20190724-03.cfg

backend webservers
    balance roundrobin
    server-template web 5 myservice.example.local:80 check resolvers mydns init-addr none

blog20190724-04.sh

$ dig @192.168.50.30 -p 53 A myservice.example.local

;; QUESTION SECTION:
;myservice.example.local.    IN  A

;; ANSWER SECTION:
myservice.example.local. 90  IN  A  192.168.50.31
myservice.example.local. 90  IN  A  192.168.50.32
myservice.example.local. 90  IN  A  192.168.50.33

blog20190724-05.cfg

backend webservers
    balance roundrobin
    server web1 192.168.50.31:80 check
    server web2 192.168.50.32:80 check
    server web3 192.168.50.33:80 check
    server web4 check disabled
    server web5 check disabled

blog20190724-06.cfg

global
    log stdout local0
    stats socket :9000 mode 660 level admin

blog20190724-07.sh

$ echo "show servers state servers" | nc localhost 9000

# be_id be_name srv_id srv_name srv_addr srv_op_state srv_admin_state srv_uweight srv_iweight srv_time_since_last_change srv_check_status srv_check_result srv_check_health srv_check_state srv_agent_state bk_f_forced_id srv_f_forced_id srv_fqdn srv_port srvrecord
3 servers 1 web1 192.168.50.33 0 32 1 1 400 7 2 0 14 0 0 0 myservice.example.local 80 -
3 servers 2 web2 192.168.50.31 0 32 1 1 290 6 3 0 14 0 0 0 myservice.example.local 80 -
3 servers 3 web3 192.168.50.32 0 32 1 1 401 7 2 0 14 0 0 0 myservice.example.local 80 -
3 servers 4 web4 - 0 32 1 1 404 1 0 0 14 0 0 0 myservice.example.local 80 -
3 servers 5 web5 - 0 32 1 1 404 1 0 0 14 0 0 0 myservice.example.local 80 -

blog20190724-08.cfg

frontend stats
    bind :8404
    stats enable
    stats uri /
    stats refresh 5s

blog20190724-09.sh

$ dig @192.168.50.30 -p 53 SRV _myservice._tcp.example.local

;; QUESTION SECTION:
;_myservice._tcp.example.local. IN      SRV

;; ANSWER SECTION:
_myservice._tcp.example.local. 0 IN     SRV     0 0 8081 host2.
_myservice._tcp.example.local. 0 IN     SRV     0 0 8080 host1.
_myservice._tcp.example.local. 0 IN     SRV     0 0 8082 host3.

;; ADDITIONAL SECTION:
host1.                  0       IN      A       192.168.50.31
host3.                  0       IN      A       192.168.50.33
host2.                  0       IN      A       192.168.50.32

blog20190724-10.cfg

backend webservers
   balance roundrobin
   server-template web 5 _myservice._tcp.example.local resolvers mydns check init-addr none

blog20190724-11.sh

 echo "show servers state servers" | nc localhost 9000

# be_id be_name srv_id srv_name srv_addr srv_op_state srv_admin_state srv_uweight srv_iweight srv_time_since_last_change srv_check_status srv_check_result srv_check_health srv_check_state srv_agent_state bk_f_forced_id srv_f_forced_id srv_fqdn srv_port srvrecord
3 servers 1 web1 192.168.50.33 0 0 1 1 3 5 0 0 7 0 0 0 host3 8082 _myservice._tcp.example.local
3 servers 2 web2 192.168.50.32 0 0 1 1 1 7 2 0 6 0 0 0 host2 8081 _myservice._tcp.example.local
3 servers 3 web3 192.168.50.31 2 0 1 1 3 6 3 4 6 0 0 0 host1 8080 _myservice._tcp.example.local
3 servers 4 web4 - 0 0 1 1 2 5 2 0 6 0 0 0 - 0 _myservice._tcp.example.local
3 servers 5 web5 - 0 0 1 1 2 5 2 0 6 0 0 0 - 0 _myservice._tcp.example.local

blog20190724-12.cfg

backend webservers
    balance roundrobin
    server web1 192.168.50.33:8082 check
    server web2 192.168.50.32:8081 check
    server web3 192.168.50.31:8080 check
    server web4 check disabled
    server web5 check disabled