背景

网络架构中需要遇到apisix，想做个apisix 访问出错的兜底方案

nginx配置

其中http://11.11.11.11:9080 是apisix访问地址

server {
	listen       80;
	server_name  sfimplat;
	index  index.html index.htm;
	root   /app/sfimplat_micro/web;
	#charset koi8-r;
	access_log  logs/access.log  main;
	
	location /sfimplat {
		proxy_set_header Host $host;
		proxy_set_header   X-Real-IP        $remote_addr;
		proxy_set_header   X-Forwarded-For  $proxy_add_x_forwarded_for;
		proxy_pass http://11.11.11.11:9080;

	} 

	error_page   500 502 503 504  /50x.html;

	location = /40x.html {
		root   html;
	}
	location = /50x.html {
		root   html;
	}
}

实操

error_page 可以捕获状态码，因此最开始我是这样配置的

server {
	listen       80;
	server_name  sfimplat;
	index  index.html index.htm;
	root   /app/sfimplat_micro/web;
	access_log  logs/access.log  main;
	
	location /sfimplat {
		proxy_set_header Host $host;
		proxy_set_header   X-Real-IP        $remote_addr;
		proxy_set_header   X-Forwarded-For  $proxy_add_x_forwarded_for;
		proxy_pass http://11.11.11.11:9080;

	}

	location @fallback {
		proxy_pass http://11.11.11.11:18084;
	}  

	#error_page   500 502 503 504  /50x.html;
	error_page 503 = @fallback;

	location = /40x.html {
		root   html;
	}
	location = /50x.html {
		root   html;
	}
}

反复试验后发现流量无法转入 location @fallback

后来发现 error_page默认仅仅捕获nginx本身的响应状态码，如果想捕获到nginx的upstream的状态码，应该配置proxy_intercept_errors on;

server {
	listen       80;
	server_name  sfimplat;
	index  index.html index.htm;
	root   /app/sfimplat_micro/web;
	access_log  logs/access.log  main;


	location /sfimplat {
		proxy_set_header Host $host;
		proxy_set_header   X-Real-IP        $remote_addr;
		proxy_set_header   X-Forwarded-For  $proxy_add_x_forwarded_for;
		proxy_pass http://11.11.11.11:9080;
		proxy_intercept_errors on;
		error_page 503 = @fallback;
	}

	location @fallback {
		proxy_set_header Host $host;
		proxy_set_header   X-Real-IP        $remote_addr;
		proxy_set_header   X-Forwarded-For  $proxy_add_x_forwarded_for;
		proxy_pass http://11.11.11.11:18084;
	}  

	error_page   500 502 503 504  /50x.html;

	location = /40x.html {
		root   html;
	}
	location = /50x.html {
		root   html;
	}
}

参考资料：
http://nginx.org/en/docs/http/ngx_http_core_module.html#error_page
http://nginx.org/en/docs/http/ngx_http_proxy_module.html#proxy_intercept_errors
https://stackoverflow.com/questions/66651410/nginx-fallback-to-alternative-upstream-on-502-and-503