HAProxy cheatsheet

Service and config

Command	Description
`systemctl status haproxy`	Service status
`systemctl reload haproxy`	Reload config (graceful)
`haproxy -c -f /etc/haproxy/haproxy.cfg`	Validate config syntax
`haproxy -vv`	Version and build info

Stats and monitoring

Command / URL	Description
`echo "show stat" \| socat stdio /run/haproxy/admin.sock`	Stats via socket
`echo "show info" \| socat stdio /run/haproxy/admin.sock`	Runtime info
`http://host:8404/stats`	Stats web UI (if enabled)
`journalctl -u haproxy -f`	Follow service logs
`ss -tlnp \| grep haproxy`	Check listeners

Runtime socket commands

To query the socket non-interactively from your terminal bash command line, pipe your command string straight into the socat network utility, for example: echo "show info" | sudo socat stdio unix-connect:/var/run/haproxy.sock

Command	Description
`show servers state <backend>`	Server UP/DOWN state
`disable server <backend>/<server>`	Drain a server
`enable server <backend>/<server>`	Re-enable a server
`show errors`	Recent HAProxy errors

Minimal HTTP load balancer

global
    log /dev/log local0
    maxconn 4096

defaults
    log     global
    mode    http
    option  httplog
    timeout connect 5s
    timeout client  50s
    timeout server  50s

frontend http_front
    bind *:80
    default_backend app_servers

backend app_servers
    balance roundrobin
    option httpchk GET /health
    server app1 10.0.1.10:8080 check
    server app2 10.0.1.11:8080 check

ACL routing example

frontend http_front
    bind *:80
    acl is_api path_beg /api
    use_backend api_servers if is_api
    default_backend web_servers

Pro tips

Always haproxy -c before reload — bad config can stop the daemon
Check the stats page first when backends show DOWN — health check path may be wrong
Use option forwardfor so backends see real client IPs
Drain servers with disable server before maintenance, then re-enable

Practice scenarios

Hands-on HAProxy scenarios on live Linux VMs: haproxy