haproxy: enable direct connections apart from pgbouncer ones (#548)

[jimnydev]

This is a tackle at #548

It's a draft, just to double check with you if you'd go this way (say, variable names). I'm not sure if we should provide a direct connections to individual replicas (so I've just provided a generic one, initially).

Also, HAProxy config is added at the end of existing stuff. I can split it so that master and replicas are grouped within existing previous sections (although it would duplicate the check if it should be included).

Thanks!

[vitabaks]

Test

listen master
    bind 10.172.0.20:5000
    maxconn 10000
    option tcplog
    option httpchk OPTIONS /primary
    http-check expect status 200
    default-server inter 3s fastinter 1s fall 3 rise 4 on-marked-down shutdown-sessions
 server pgnode01 10.172.0.20:6432 check port 8008
 server pgnode02 10.172.0.21:6432 check port 8008
 server pgnode03 10.172.0.22:6432 check port 8008

listen master_direct
    bind 10.172.0.20:6000
    maxconn 10000
    option tcplog
    option httpchk OPTIONS /primary
    http-check expect status 200
    default-server inter 3s fastinter 1s fall 3 rise 4 on-marked-down shutdown-sessions
 server pgnode01 10.172.0.20:5432 check port 8008
 server pgnode02 10.172.0.21:5432 check port 8008
 server pgnode03 10.172.0.22:5432 check port 8008

listen replicas
    bind 10.172.0.20:5001
    maxconn 10000
    option tcplog
    option httpchk OPTIONS /replica
    balance roundrobin
    http-check expect status 200
    default-server inter 3s fastinter 1s fall 3 rise 2 on-marked-down shutdown-sessions
 server pgnode01 10.172.0.20:6432 check port 8008
 server pgnode02 10.172.0.21:6432 check port 8008
 server pgnode03 10.172.0.22:6432 check port 8008

listen replicas_direct
    bind 10.172.0.20:6001
    maxconn 10000
    option tcplog
    option httpchk OPTIONS /replica
    balance roundrobin
    http-check expect status 200
    default-server inter 3s fastinter 1s fall 3 rise 2 on-marked-down shutdown-sessions
 server pgnode01 10.172.0.20:5432 check port 8008
 server pgnode02 10.172.0.21:5432 check port 8008
 server pgnode03 10.172.0.22:5432 check port 8008

root@pgnode01:/# systemctl stop pgbouncer
root@pgnode01:/# systemctl stop pgbouncer-2
root@pgnode01:/# psql -h 10.172.0.20 -p 5000 -U postgres
^C
root@pgnode01:/# psql -h 10.172.0.20 -p 6000 -U postgres
Password for user postgres: 
psql (16.1 (Ubuntu 16.1-1.pgdg22.04+1))
SSL connection (protocol: TLSv1.3, cipher: TLS_AES_256_GCM_SHA384, compression: off)
Type "help" for help.

postgres=# \q
root@pgnode01:/# psql -h 10.172.0.20 -p 6001 -U postgres
Password for user postgres: 
psql (16.1 (Ubuntu 16.1-1.pgdg22.04+1))
SSL connection (protocol: TLSv1.3, cipher: TLS_AES_256_GCM_SHA384, compression: off)
Type "help" for help.

postgres=# \q

passed