聊聊nginx与tomcat的5xx

序

本文主要讲述一下nginx与tomcat的502、504、503错误及其常见的产生原因。

502

定义

502 Bad Gateway : 作为网关或者代理工作的服务器尝试执行请求时，从上游服务器接收到无效的响应。

常见原因

后端服务挂了的情况,直接502
后端服务在重启

实例

将后端服务关掉，然后向nginx发送请求后端接口，日志如下：

access.log 127.0.0.1 - - [22/Dec/2017:20:44:38 +0800] "GET /timeout/long-write HTTP/1.1" 502 537 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/63.0.3239.108 Safari/537.36"
error.log 2017/12/22 20:45:12 [error] 1481#0: *3 kevent() reported that connect() failed (61: Connection refused) while connecting to upstream, client: 127.0.0.1, server: localhost, request: "GET /timeout/long-write HTTP/1.1", upstream: "http://[::1]:8080/timeout//long-write", host: "localhost:8888"

504

定义

504:gateway timeout.作为网关或者代理工作的服务器尝试执行请求时，未能及时从上游服务器（URI标识出的服务器，例如HTTP、FTP、LDAP）或者辅助服务器（例如DNS）收到响应。注意：某些代理服务器在DNS查询超时时会返回400或者500错误

常见原因

该接口太耗时，后端服务接收到请求，开始执行，未能在设定时间返回数据给nginx
后端服务器整体负载太高，接受到请求之后，由于线程繁忙，未能安排给请求的接口，导致未能在设定时间返回数据给nginx

实例

前端返回 <html> <head><title>504 Gateway Time-out</title></head> <body bgcolor="white"> <center><h1>504 Gateway Time-out</h1></center> <hr><center>openresty/1.9.15.1</center> </body> </html>
access.log 192.168.99.1 - - [22/Dec/2017:21:58:20 +0800] "GET /timeout/long-resp HTTP/1.1" 504 591 "-" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/63.0.3239.108 Safari/537.36" "-" "-"
error.log 2017/12/22 21:58:20 [error] 5#5: *7 upstream timed out (110: Connection timed out) while reading response header from upstream, client: 192.168.99.1, server: , request: "GET /timeout/long-resp HTTP/1.1", upstream: "http://192.168.99.100:8080/timeout//long-resp", host: "192.168.99.100:8686"
nginx.conf location /timeout/long-resp { proxy_connect_timeout 30; proxy_read_timeout 100; proxy_send_timeout 10; proxy_pass http://192.168.99.100:8080/timeout/long-resp ; }
java代码 @GetMapping("/timeout/long-resp") public String longResp() throws InterruptedException { TimeUnit.SECONDS.sleep(120); return "finish"; } 服务器接受请求一直没有返回,nginx在等待100秒后报Connection timed out,返回504；但是后端继续执行，在第120秒才执行完。

503(`相对少见`)

定义

503表示service unavailable，表示服务器当前处于暂时不可用状态，无论是有意还是无意，当服务器端处于无法应答的状态时，就会返回该状态码。其中，服务端因维护需要而停止服务属于有意的情况。而当服务器自身负载过高，处于无法响应的状态时，则属于无意的情况。另外，负载均衡器或者web服务器的前置机等这些地方的服务器也有可能返回503.

常见原因

nginx进行限流，超过限速则返回503
后端服务进行常规维护，比如pause tomcat

nginx限流返回503实例

config http{ ## test 503 limit_conn_zone $binary_remote_addr zone=addr:10m; server { listen 8686; location /timeout { limit_conn addr 1; proxy_connect_timeout 30; proxy_read_timeout 100; proxy_send_timeout 2; proxy_pass http://192.168.99.100:8080/timeout/ ; } } }
error.log 2017/12/24 20:58:29 [error] 5#5: *1473 limiting connections by zone "addr", client: 192.168.99.1, server: , request: "GET /timeout/busy HTTP/1.1", host: "192.168.99.100:8686"
access.log 192.168.99.1 - - [24/Dec/2017:20:58:39 +0800] "GET /timeout/busy HTTP/1.1" 503 219 "-" "-" "-" "-"
client wrk -t12 -c200 -d100s -T60s --latency http://192.168.99.100:8686/timeout/busy ➜ ~ curl -i http://192.168.99.100:8686/timeout/busy HTTP/1.1 503 Service Temporarily Unavailable Server: openresty/1.9.15.1 Date: Sun, 24 Dec 2017 12:58:26 GMT Content-Type: text/html Content-Length: 219 Connection: keep-alive <html> <head><title>503 Service Temporarily Unavailable</title></head> <body bgcolor="white"> <center><h1>503 Service Temporarily Unavailable</h1></center> <hr><center>openresty/1.9.15.1</center> </body> </html>

tomcat返回503实例

Http11Processor tomcat-embed-core-8.5.23-sources.jar!/org/apache/coyote/http11/Http11Processor.java @Override public SocketState service(SocketWrapperBase<?> socketWrapper) throws IOException { RequestInfo rp = request.getRequestProcessor(); rp.setStage(org.apache.coyote.Constants.STAGE_PARSE); // Setting up the I/O setSocketWrapper(socketWrapper); inputBuffer.init(socketWrapper); outputBuffer.init(socketWrapper); // Flags keepAlive = true; openSocket = false; readComplete = true; boolean keptAlive = false; SendfileState sendfileState = SendfileState.DONE; while (!getErrorState().isError() && keepAlive && !isAsync() && upgradeToken == null && sendfileState == SendfileState.DONE && !endpoint.isPaused()) { //...... if (endpoint.isPaused()) { // 503 - Service unavailable response.setStatus(503); setErrorState(ErrorState.CLOSE_CLEAN, null); } else { keptAlive = true; // Set this every time in case limit has been changed via JMX request.getMimeHeaders().setLimit(endpoint.getMaxHeaderCount()); if (!inputBuffer.parseHeaders()) { // We've read part of the request, don't recycle it // instead associate it with the socket openSocket = true; readComplete = false; break; } if (!disableUploadTimeout) { socketWrapper.setReadTimeout(connectionUploadTimeout); } } } } 只要endpoint的状态是paused，则返回503
AbstractEndpoint tomcat-embed-core-8.5.23-sources.jar!/org/apache/tomcat/util/net/AbstractEndpoint.java /** * Pause the endpoint, which will stop it accepting new connections. */ public void pause() { if (running && !paused) { paused = true; unlockAccept(); getHandler().pause(); } } /** * Resume the endpoint, which will make it start accepting new connections * again. */ public void resume() { if (running) { paused = false; } } 这里是endpoint的pause以及resume方法
请求当请求进入Http11Processor的service方法到执行endpoint.isPaused()方法期间，tomcat被pause了，这个时候，就会返回503，如下： ➜ ~ curl -i http://localhost:8080/demo/test HTTP/1.1 503 Transfer-Encoding: chunked Date: Sun, 24 Dec 2017 14:10:16 GMT Connection: close

小结

502 通常是后端服务挂了或在重启
504 通常是请求的接口执行耗时，亦或是后端服务负载高，执行耗时
503 通常是nginx限流或后端服务pause进行维护

doc

Nginx状态码总结
nginx错误502，503，504分析
Nginx 502 503 错误触发条件与解决办法汇总

聊聊nginx与tomcat的5xx

序

502

定义

常见原因

实例

504

定义

常见原因

实例

503(相对少见)

定义

常见原因

nginx限流返回503实例

tomcat返回503实例

小结

doc

503(`相对少见`)