RTFM · Healthchecks

lb.saphira.sendexpect.tcp: the custom-protocol escape hatch

For every protocol nobody wrote a check for: send exact bytes, demand a matching answer. Binary or text, fixed or hex, with a configurable pause between connect and send; this is the check you write against in an afternoon.

What it proves

Whatever transaction you define: the check connects to real:$4, sends your payload, accumulates the response, and is healthy only when the response matches your regex within the timeout. The regex runs over the accumulated buffer (latin-1, dot-matches-newline), so multi-packet answers work naturally.

How it works

The probe engine's sendexpect probe in TCP mode. Payload sources, in priority order: LB_SAPHIRA_SEND (text), LB_SAPHIRA_SEND_HEX (hex, spaces and colons ignored), LB_SAPHIRA_SEND_FILE (raw file; the escape hatch's escape hatch for long binary frames). LB_SAPHIRA_DELAY sleeps between connect and send for protocols that need the server to speak first.

Waiting for a banner? Leave SEND unset and use the ssh-style banner probe via saphira-lb-probe banner, or just set EXPECT and SEND together for a full conversation.

Configuration

Knobs
Variable	Default	Meaning
LB_SAPHIRA_SEND / SEND_HEX / SEND_FILE	(required)	The payload: one of the three
LB_SAPHIRA_EXPECT	(required)	Regex the accumulated response must match
LB_SAPHIRA_DELAY	0	Seconds between connect and send
LB_SAPHIRA_TIMEOUT	3	Whole-exchange deadline
(target port)	$4, else $2	Any TCP port

Wiring it up

ldirectord

# ldirectord.cf - legacy ERP listener
virtual = 203.0.113.10:7777
    protocol = tcp
    scheduler = lc
    real = 192.168.20.140:7777 gate 1
    checktype = external
    checkcommand = "/var/lib/lb/saphira/lb.saphira.sendexpect.tcp"

A binary keepalive, defined in config

# /etc/saphira/lb-healthchecks.d/sendexpect.tcp/erp.conf
LB_SAPHIRA_SEND_HEX=01 00 00 00
LB_SAPHIRA_EXPECT=^ACK

Run it by hand

Manual run

LB_SAPHIRA_SEND='PING' LB_SAPHIRA_EXPECT='PONG' \
  /var/lib/lb/saphira/lb.saphira.sendexpect.tcp erp 7777 192.168.20.140 7777
echo $?
# 0 = reply matched
# 1 = connect refused, timeout, or reply never matched
# 2 = payload or expect not configured

Failure modes

Timeout mid-exchange: the server accepted and went quiet: the payload may be wrong for the dialect
Never matched: right service, wrong regex: debug with saphira-lb-probe sendexpect directly and watch the reply
exit 2: missing payload or expect: the check refuses to guess

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