nginx still use the down peer

I use ngx.upstream.get_primary_peers and find a peer is down。But nginx still use the bad peer。

log：
2018/10/12 16:14:36 [debug] 1998#1998: *508497 [lua] test.lua:21: gen_peers_status_info(): name:123.157.76.2:80stat: up

2018/10/12 16:14:36 [debug] 1998#1998: *508497 [lua] test.lua:21: gen_peers_status_info(): name:123.157.76.5:80stat: DOWN

2018/10/12 16:14:36 [debug] 1998#1998: *508497 [lua] test.lua:21: gen_peers_status_info(): name:60.217.244.95:80stat: up

2018/10/12 16:14:36 [debug] 1998#1998: *508497 http cleanup add: 0000000003439608
2018/10/12 16:14:36 [debug] 1998#1998: *508497 http script var: "/a64/0/ads11euyc1dsa0pb.dsaudio"
2018/10/12 16:14:36 [debug] 1998#1998: *508497 consistent hash [peer name]:123.157.76.5:80 4170160978
2018/10/12 16:14:36 [debug] 1998#1998: *508497 stream socket 18

lua file:
local u = "test.domain.com"
local ok, upstream = pcall(require, "ngx.upstream")
if not ok then
error("ngx_upstream_lua module required")
end
local set_peer_down = upstream.set_peer_down
local get_primary_peers = upstream.get_primary_peers
local get_backup_peers = upstream.get_backup_peers
local get_upstreams = upstream.get_upstreams

local function gen_peers_status_info(peers)
local npeers = #peers
for i = 1, npeers do
local peer = peers[i]
local stat = ""
if peer.down then
stat = " DOWN\n"
else
stat = " up\n"
end
ngx.log(ngx.DEBUG,"name:",peer.name,"stat:",stat)
end
return idx
end

local peers, err = get_primary_peers(u)
if not peers then
return "failed to get primary peers in upstream " .. u .. ": "
.. err
end
gen_peers_status_info(peers)
peers, err = get_backup_peers(u)
if not peers then
return "failed to get backup peers in upstream " .. u .. ": "
.. err
end
gen_peers_status_info(peers)

upstream config ：
upstream test.domain.com {
consistent_hash $uri;
#server 123.157.76.2:80 id=1001 weight=1 max_fails=2 fail_timeout=30s;
#server 123.157.76.5:80 id=1002 weight=1 max_fails=2 fail_timeout=30s;
server 123.157.76.2:80;
server 123.157.76.5:80;

    server 60.217.244.95:80 backup;
}

Start by reproducing the reported selection with the Lua code in test.lua and the supplied test.domain.com upstream configuration. Trace the get_primary_peers result through the consistent-hash request path, then determine whether the down peer should be excluded and add a regression test if the relevant test location is found. Done means the reported down peer is no longer selected, or the issue is explained as expected behavior.