gistfile1.txt

http {
  lua_shared_dict healthchecks            1m;

  upstream YOURAPP {
    server 0.0.0.1;   # just an invalid address as a place holder

    balancer_by_lua_block {
        local balancer = require "ngx.balancer"

        -- well, usually we calculate the peer's host and port
        -- according to some balancing policies instead of using
        -- hard-coded values like below
        local host = "127.0.0.2"
        local port = 8080

        local ok, err = balancer.set_current_peer(host, port)
        if not ok then
            ngx.log(ngx.ERR, "failed to set the current peer: ", err)
            return ngx.exit(500)
        end
    }
  }

  keepalive 10;  # connection pool
  };
  
  server {
    init_worker_by_lua_block {
      local hc = require "resty.upstream.healthcheck"

      local ok, err = hc.spawn_checker{
          shm = "healthchecks",  -- defined by "lua_shared_dict"
          upstream = "YOURAPP",  -- defined by "upstream"
          type = "http",

          -- get /healthcheck with a host header
          http_req = "GET /healthcheck HTTP/1.0\r\nHost: some.host.header.if.needed.com\r\n\r\n",

          interval = 2000,  -- run the check cycle every 2 sec
          timeout = 1000,   -- 1 sec is the timeout for network operations
          fall = 3,         -- # of successive failures before turning a peer down
          rise = 2,         -- # of successive successes before turning a peer up

          -- Adding 301 as an acceptable response code in case the route changes somehow
          valid_statuses = {200},  -- a list valid HTTP status code (indicating a healthy upstream)
          concurrency = 10,        -- concurrency level for test requests
      }

      if not ok then
          ngx.log(ngx.ERR, "failed to spawn health checker: ", err)
          return
      end
    }


    location /healthcheck { 
      default_type application/json;

      # Determine if the upstream is healthy by having atleast 1 healthy server
      content_by_lua_block {
        local cjson = require("cjson")
        -- Pcall to avoid barfing on old versions of resty
        local ok, upstream = pcall(require, "ngx.upstream")
        if not ok then
            ngx.status = ngx.HTTP_INTERNAL_SERVER_ERROR
            ngx.log(ngx.ERR, "ngx_upstream_lua module required")
            ngx.exit(ngx.HTTP_INTERNAL_SERVER_ERROR)
            return
        end

        -- This is gonna ugly 
        -- Time is short.. do better 
        local ret = { Status = "DOWN", Data = {} }

        local us, err = upstream.get_upstreams()
        if not us then
            ngx.status = ngx.HTTP_INTERNAL_SERVER_ERROR
            ngx.say(ret)
            ngx.log(ngx.ERR, "failed to get upstream names: " .. err)
            ngx.exit(ngx.HTTP_INTERNAL_SERVER_ERROR)
            return
        end

        local n = #us
        local found = false
        local down = false
        for i = 1, n do
          local u = us[i]
          if u == "YOURAPP" then
            found = true
            local peers, err = upstream.get_primary_peers(u)
            if not peers then
              ret.Error = "failed to get primary peers in upstream " .. u .. ": " .. err
              ngx.status = ngx.HTTP_INTERNAL_SERVER_ERROR
              ngx.say(cjson.encode(ret))
              ngx.log(ngx.ERR, "failed to get primary peers in upstream " .. u .. ": " .. err)
              ngx.exit(ngx.HTTP_INTERNAL_SERVER_ERROR)
              return
            end

            ret.Data = peers

            -- Terminate upstream loop
            break
          end
        end

        if #ret.Data == 0 then
          ngx.status = ngx.HTTP_INTERNAL_SERVER_ERROR
          ngx.say(cjson.encode(ret))
          ngx.exit(ngx.HTTP_INTERNAL_SERVER_ERROR)
          return
        end

        if ret.Data[1].down then
          ngx.status = ngx.HTTP_INTERNAL_SERVER_ERROR
          ngx.say(cjson.encode(ret))
          ngx.exit(ngx.HTTP_INTERNAL_SERVER_ERROR)
          return
        else
          ret.Status = "UP"
          ret.Data[1].down = false
          ngx.status = ngx.HTTP_OK
          ngx.say(cjson.encode(ret))
          ngx.exit(ngx.HTTP_OK)
          return
        end
      }
    }
  }
}