chore: cache the error message when create new `healthcheck` instance

[membphis]

healthcheck.new may fail, we need to check the return value first.

apisix/apisix/balancer.lua

Line 90 in 4d316bc

local checker = healthcheck.new({

here is the doc:

[membphis]

The patch, it maybe useful for you. welcome PR ^_^

diff --git a/apisix/balancer.lua b/apisix/balancer.lua
index d80cb676..c644bdc3 100644
--- a/apisix/balancer.lua
+++ b/apisix/balancer.lua
@@ -87,11 +87,15 @@ local function create_checker(upstream, healthcheck_parent)
     if healthcheck == nil then
         healthcheck = require("resty.healthcheck")
     end
-    local checker = healthcheck.new({
+    local checker, err = healthcheck.new({
         name = "upstream#" .. healthcheck_parent.key,
         shm_name = "upstream-healthcheck",
         checks = upstream.checks,
     })
+    if not checker then
+        core.log.error("fail to create healthcheck instance: ", err)
+        return
+    end

     local host = upstream.checks and upstream.checks.active and upstream.checks.active.host
     local port = upstream.checks and upstream.checks.active and upstream.checks.active.port