当使用nginx代理多个网关实例时,
当被请求服务的get 接口异常时,如 error timeout invalid_header http_500 http_502 http_503 http_504,
nginx 会响应 502状态码,
在我之前的认知里,nginx 只会转发 后端服务的响应,一般不会对状态码进行修改
nginx 配置如下:
worker_processes 1;
daemon off;
master_process off;
error_log logs/error.log debug;
events {
worker_connections 1024;
}
http {
include mime.types;
default_type application/octet-stream;
log_format apm '[$time_local]tclient=$remote_addrt'
'upstream_addr=$upstream_addrt'
'upstream_status=$upstream_statust'
'document_root="$document_root"t'
'fastcgi_script_name="$fastcgi_script_name"t'
'request_filename="$request_filename"t'
'request_time=$request_timet'
'upstream_response_time=$upstream_response_timet'
'upstream_connect_time=$upstream_connect_timet'
'upstream_header_time=$upstream_header_timet';
access_log logs/access.log apm;
sendfile on;
keepalive_timeout 65;
upstream gateway {
server 192.168.2.102:12012;
server 192.168.2.102:12011;
}
server {
listen 80;
server_name localhost;
location / {
root html;
index index.html index.htm;
}
location /api/ {
proxy_pass http://gateway/;
proxy_next_upstream error http_503 http_502;
}
error_page 500 502 503 504 /50x.html;
location = /50x.html {
root html;
}
}
}
示例测试代码:
@GetMapping("/excep503")
public ResponseEntity excep503(HttpServletRequest request, Integer times) throws InterruptedException {
Thread.sleep(200);
return ResponseEntity.status(HttpStatus.SERVICE_UNAVAILABLE).body("服务不可用");
}
测试方法:
多次 get 请求一个异常接口
现象:
有时报错 502 ,有时报错 503
返回 503时
access_log 中的 upstream_addr 会有两条: 192.168.2.102:12012, 192.168.2.102:12011
error_log 会出现分别请求 两台网关的日志:
首先请求 connect to 192.168.2.102:12011 ;
102:12011 返回 503 Service Unavailable
报错
upstream server temporarily disabled while re服务器托管网ading response header from upstream
然后 重新指向 connect to 192.168.2.102:12012
102:12012 同样 返回 503 Service Unavailable
返回 502时
access_log 中的 upstream_addr 只会有一条:upstream_addr=192.168.2.102:12011
error_log 只会出现一次请求网关的日志:
请求 connect to 192.168.2.102:12011 ;
102:12011 返回 503 Service Unavailable
报错
upstream server temporarily disabled while reading response header from upstream,
no live upstreams while connecting to upstream,
返回502的原因
根据 查阅相关资料
传入的ft_type为 40000000 匹配到 default ,所以最终状态码为 NGX_HTTP_BAD_GATEWAY ,即 502
nginx-1.24.0srchttpngx_http_upstream.c(ngx_http_upstream_next) 4370行;
switch (ft_type) {
case NGX_HTTP_UPSTREAM_FT_TIMEOUT:
case NGX_HTTP_UPSTREAM_FT_HTTP_504:
status = NGX_HTTP_GATEWAY_TIME_OUT;
break;
case NGX_HTTP_UPSTREAM_FT_HTTP_500:
status = NGX_HTTP_INTERNAL_SERVER_ERROR;
break;
case NGX_HTTP_UPSTREAM_FT_HTTP_503:
status = NGX_HTTP_SERVICE_UNAVAILABLE;
break;
/*
* NGX_HTTP_UPSTREAM_FT_BUSY_LOCK and NGX_HTTP_UPSTREAM_FT_MAX_WAITING
* never reach here
*/
default:
status = NGX_HTTP_BAD_GATEWAY;
}
502 与 503 的 逻辑分岔路:
nginx-1.24.0srchttpngx_http_upstream_round_robin.c(ngx_http_upstream_get_round_robin_peer)449 行
peers = rrp->peers;
ngx_http_upstream_rr_peers_wlock(peers);
if (peers->single) {
peer = peers->peer;
if (peer->down) {
goto failed;
}
if (peer->max_conns && peer->conns >= peer->max_conns) {
goto failed;
}
rrp->current = peer;
} else {
peer = ngx_http_upstream_get_peer(rrp);
if (peer == NULL) {
goto failed;
}
ngx_log_debug2(NGX_LOG_DEBUG_HTTP, pc->log, 0,
"get rr peer, current: %p %i",
服务器托管网 peer, peer->current_weight);
}
其中的 single 标志位是一个用于标识后端服务器组是否只有一个成员的标志,即 upstream_addr 为单个
所以现在的问题是:
为什么 有时upstream_addr是两个 ,有时是一个
debug nginx 源码
nginx启动时 给每个后端节点赋值了一个默认的超时时间 10s
发生异常时将节点标记为不可用:
nginx-1.24.0/src/http/ngx_http_upstream_round_robin.c(ngx_http_upstream_get_peer) 522 行
for (peer = rrp->peers->peer, i = 0;
peer;
peer = peer->next, i++)
{
n = i / (8 * sizeof(uintptr_t));
m = (uintptr_t) 1 tried[n] & m) {
continue;
}
if (peer->down) {
continue;
}
if (peer->max_fails
&& peer->fails >= peer->max_fails
&& now - peer->checked fail_timeout)
{
continue;
}
if (peer->max_conns && peer->conns >= peer->max_conns) {
continue;
}
peer->current_weight += peer->effective_weight;
total += peer->effective_weight;
if (peer->effective_weight weight) {
peer->effective_weight++;
}
if (best == NULL || peer->current_weight > best->current_weight) {
best = peer;
p = i;
}
}
验证
不断请求接口,发现每过10秒,就会恢复503 错误,符合猜测
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