Dockerfile

FROM haproxy:2.3
COPY haproxy.cfg /usr/local/etc/haproxy/haproxy.cfg

fly.toml

app = "haproxy-scratch"

kill_signal = "SIGINT"
kill_timeout = 5

[experimental]
  private_network=true

[[services]]
  internal_port = 8085
  protocol = "tcp"

  [services.concurrency]
    hard_limit = 25
    soft_limit = 20

  [[services.ports]]
    handlers = ["http"]
    port = "80"

  [[services.ports]]
    handlers = ["tls", "http"]
    port = "443"

  [[services.tcp_checks]]
    grace_period = "1s"
    interval = "15s"
    port = "8085"
    restart_limit = 6
    timeout = "2s"

haproxy.cfg

global
defaults
	mode tcp
	timeout connect		30s
	timeout client		30s
	timeout server		30s

frontend http_front
   bind *:8085
   default_backend http_back

backend http_back
   server tinypilot tinypilot._peer.internal:80