T6246: improve haproxy http check configuration

[nvollmar]

Change Summary

Improve upon issues raised in backport PR #3332

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

https://vyos.dev/T6246

Related PR(s)

#3325
#3332

Component(s) name

load-balancing

Proposed changes

Improve

How to test

set load-balancing reverse-proxy service front port 4433
set load-balancing reverse-proxy service front backend bk-01

set load-balancing reverse-proxy backend bk-01 mode tcp
set load-balancing reverse-proxy backend bk-01 server s01 address 192.0.2.11
set load-balancing reverse-proxy backend bk-01 server s01 port 4438


set load-balancing reverse-proxy backend bk-01 http-check method get
set load-balancing reverse-proxy backend bk-01 http-check uri /health

set load-balancing reverse-proxy backend bk-01 http-check expect status 200

Should result in a config /run/haproxy/haproxy.cfg

# Frontend
frontend front
    bind :::4433 v4v6  
    default_backend bk-01


# Backend
backend bk-01
    option httpchk
    http-check send meth GET uri /health
    http-check expect status 200
    balance roundrobin
    mode tcp
    server s01 192.0.2.11:4438 

Smoketest result

$ /usr/libexec/vyos/tests/smoke/cli/test_load-balancing_reverse-proxy.py
test_01_lb_reverse_proxy_domain (__main__.TestLoadBalancingReverseProxy.test_01_lb_reverse_proxy_domain) ... ok
test_02_lb_reverse_proxy_cert_not_exists (__main__.TestLoadBalancingReverseProxy.test_02_lb_reverse_proxy_cert_not_exists) ... 
PKI does not contain any certificates!


Certificate "cert" not found in configuration!

ok
test_03_lb_reverse_proxy_ca_not_exists (__main__.TestLoadBalancingReverseProxy.test_03_lb_reverse_proxy_ca_not_exists) ... ok
test_04_lb_reverse_proxy_backend_ssl_no_verify (__main__.TestLoadBalancingReverseProxy.test_04_lb_reverse_proxy_backend_ssl_no_verify) ... 
backend bk-01 cannot have both ssl options no-verify and ca-certificate
set!

ok
test_05_lb_reverse_proxy_backend_http_check (__main__.TestLoadBalancingReverseProxy.test_05_lb_reverse_proxy_backend_http_check) ... ok

----------------------------------------------------------------------
Ran 5 tests in 82.459s

OK

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly