tcp-check expect with exclamation mark

[Dmitriy Kuzmin]

Greetings

I’m using haproxy to load balance readonly queries between redis slaves.
I want to use health check system to exclude slaves from load balancing,
that are in a process of sync with master.
The idea is to look for a string “master_sync_in_progress:1” in response to
“info replication”.
If this string is found then backend should be marked as down.

I’m trying to use “tcp-check expect ! string” (with exclamation mark [!])
to get this working, but backends are permanently down regardless of sync
status.
During sync (slave’s response contains “master_sync_in_progress:1”) health
check status is “L7RSP,TCPCHK matched unwanted content
'master_sync_in_progress:1' at step 5”.
However, when slave’s response contains “master_sync_in_progress:0” (sync
finished) health check status is “L7TOUT, at step 5 of tcp-check (expect
string 'master_sync_in_progress:1’)”.

Does negation with exclamation mark (!) work with tcp-check at all?

I’ve observed this behaviour in haproxy 1.5.18, 1.7.11 and 1.8.9


Example configuration:

global
    log               127.0.0.1 local2
    chroot            /var/lib/haproxy
    pidfile           /var/run/haproxy.pid
    maxconn           4000
    user              haproxy
    group             haproxy
    daemon

defaults
    mode                        tcp
    log                         global
    option                      tcplog
    option                      dontlognull
    option                      redispatch
    retries                     3
    timeout http-request        10s
    timeout queue               1m
    timeout connect             10s
    timeout client              1m
    timeout server              1m
    timeout http-keep-alive     10s
    timeout check               10s
    maxconn                     3000

frontend redis_reads_ft
    bind        /var/run/haproxy/redis_reads
    use_backend redis_reads_bk

backend redis_reads_bk
    option log-health-checks
    balance   roundrobin

    option    tcp-check
    tcp-check connect
    tcp-check send PING\r\n
    tcp-check expect string +PONG
    tcp-check send info\ replication\r\n
    tcp-check expect ! string master_sync_in_progress:1
    tcp-check send QUIT\r\n
    tcp-check expect string +OK

    server sc-redis1_63811 10.10.68.61:63811 check
    server sc-redis1_63812 10.10.68.61:63812 check
    server sc-redis1_63813 10.10.68.61:63813 check


Best regards,
Dmitriy Kuzmin