Report health of TCP mode frontends to external health-checks

@mattiwei wrote:

Dear all,
I am struggling with a planned setup (yes, it could be done more elegantly, but the solution has to fit into an existing setup):

• haproxy in TCP mode, load-balances between two backend servers.
• an external LB in front needs to be able to check if the frontend (= at least one backend server) is up

Now:
- When the external LB uses a TCP health check, it considers the frontend always up, because the TCP-handshake is successful (haproxy sends a RST right after the TCP handshake, but the external LB (A10) looks only at the SYN/ACK and considers the service is up).
- I can configure a separate HTTP frontend on a different port for testing purposes and have the external LB do an HTTP health check:

listen svc1
  bind 10.0.0.1:5555
  server 192.168.0.1:5555 check

frontend HEALTH-svc1
  bind 10.0.0.1:80 
  mode http
  acl service_dead nbsrv(svc1)  lt 1
  monitor-uri /health
  monitor fail if service_dead

Here's the catch:
I have about 200 TCP mode proxies configured. They all should be health-checked by the external LB, one by one. With the above configuration, I would have to define 200 additional health-check frontends, each using one dedicated TCP port, because this configuration is not intended to work:

*** NOTE CONFIG BELOW DOES NOT WORK, just an example ***
frontend HEALTH-checker
      bind 10.0.0.1:80 
      mode http

      acl svc1_dead nbsrv(svc1)  lt 1
      monitor-uri /health/svc1
      monitor fail if svc1_dead

      acl svc2_dead nbsrv(svc2)  lt 1
      monitor-uri /health/svc2
      monitor fail if svc2_dead

Or have a different approach:

Let haproxy answer to specific URLs with the status of the requested frontend:
GET /health/{frontend_name} => reply with HTTP/200 if frontend is up, HTTP/503 if frontend is down, HTTP/508 if this frontend does not exist.

Is there any way to configure HAProxy to have this functionality? If not: Can I add this to the haproxy wishlist?
Any thoughts on this? Or is there any way to have a similar functionality I missed?

Mathias Weiersmueller

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