script.lua

-- `core` is a static class provided by haproxy containing all
-- the haproxy methods we can use.

-- `register_init` registers a function to be executed after
-- configuration parsing.
core.register_init(function ()
    core.log(core.info, "script loaded: case-200-ok")
end)

-- `register_service` registers a lua function to be executed
-- as a service. Once it's been properly registered, the service
-- can be referenced in the haproxy configuration as `lua.<svc_name>`.
--
-- Depending on the mode (tcp or http), the applet is either an
-- AppletHTTP or AppletTCP class instance.
core.register_service("status_service", "http", function (applet)


    local backend_name = "simple-ad"
    local r = ""

    backend = core.proxies[backend_name]
    servers = backend["servers"]

    local any_up = false

    for k, v in pairs(servers) do

        status = v.get_stats(v)["status"]

        -- If _any_ of the servers are up, we will return OK
        if (status == "UP") then
            any_up = true
        end

    end

    if ( any_up ) then
        core.log(core.info, "Found some servers up")
        applet:set_status(200)
        r = "OK"
    else
        core.log(core.info, "Found NO servers up")
        applet:set_status(500)
        r = "FAILED"
    end

    applet:start_response()
    applet:send(r)
end)