連接失效問題
例子
其中，Redis常見的報錯就是：
配置項：timeout
報錯信息：Error while reading line from the server
Redis可以配置如果客戶端經過多少秒還不給Redis服務器發送數據，那么就會把連接close掉。
MySQL常見的報錯：
配置項：wait_timeout & interactive_timeout
報錯信息：has gone away
和Redis服務器一樣，MySQL也會定時的去清理掉沒用的連接。
如何解決
1、用的時候進行重連
2、定時發送心跳維持連接
用的時候進行重連
優點是簡單，缺點是面臨短連接的問題。
定時發送心跳維持連接
推薦。
如何維持長連接
tcp協議中實現的tcp_keepalive
操作系統底層提供了一組tcp的keepalive配置：
1 tcp_keepalive_time (integer; default: 7200; since Linux 2.2) 2 The number of seconds a connection needs to be idle before TCP 3 begins sending out keep-alive probes. Keep-alives are sent only 4 when the SO_KEEPALIVE socket option is enabled. The default 5 value is 7200 seconds (2 hours). An idle connection is 6 terminated after approximately an additional 11 minutes (9 7 probes an interval of 75 seconds apart) when keep-alive is 8 enabled. 9 10 Note that underlying connection tracking mechanisms and 11 application timeouts may be much shorter. 12 13 tcp_keepalive_intvl (integer; default: 75; since Linux 2.4) 14 The number of seconds between TCP keep-alive probes. 15 16 tcp_keepalive_probes (integer; default: 9; since Linux 2.2) 17 The maximum number of TCP keep-alive probes to send before 18 giving up and killing the connection if no response is obtained 19 from the other end. 20 8
Swoole底層把這些配置開放出來了，例如：
1 ?php 2 3 $server = new \Swoole\Server('127.0.0.1', 6666, SWOOLE_PROCESS); 4 5 $server->set([ 6 'worker_num' => 1, 7 'open_tcp_keepalive' => 1, 8 'tcp_keepidle' => 4, // 對應tcp_keepalive_time 9 'tcp_keepinterval' => 1, // 對應tcp_keepalive_intvl 10 'tcp_keepcount' => 5, // 對應tcp_keepalive_probes 11 ]);
其中：
1 'open_tcp_keepalive' => 1, // 總開關，用來開啟tcp_keepalive 2 'tcp_keepidle' => 4, // 4s沒有數據傳輸就進行檢測 3 // 檢測的策略如下： 4 'tcp_keepinterval' => 1, // 1s探測一次，即每隔1s給客戶端發一個包（然后客戶端可能會回一個ack的包，如果服務端收到了這個ack包，那么說明這個連接是活着的） 5 'tcp_keepcount' => 5, // 探測的次數，超過5次后客戶端還沒有回ack包，那么close此連接
我們來實戰測試體驗一下，服務端腳本如下：
1 <?php 2 3 $server = new \Swoole\Server('127.0.0.1', 6666, SWOOLE_PROCESS); 4 5 $server->set([ 6 'worker_num' => 1, 7 'open_tcp_keepalive' => 1, // 開啟tcp_keepalive 8 'tcp_keepidle' => 4, // 4s沒有數據傳輸就進行檢測 9 'tcp_keepinterval' => 1, // 1s探測一次 10 'tcp_keepcount' => 5, // 探測的次數，超過5次后還沒有回包close此連接 11 ]); 12 13 $server->on('connect', function ($server, $fd) { 14 var_dump("Client: Connect $fd"); 15 }); 16 17 $server->on('receive', function ($server, $fd, $reactor_id, $data) { 18 var_dump($data); 19 }); 20 21 $server->on('close', function ($server, $fd) { 22 var_dump("close fd $fd"); 23 }); 24 25 $server->start();
我們啟動這個服務器：
1 ~/codeDir/phpCode/hyperf-skeleton # php server.php
然后通過tcpdump進行抓包：
~/codeDir/phpCode/hyperf-skeleton # tcpdump -i lo port 6666 tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on lo, link-type EN10MB (Ethernet), capture size 262144 bytes
我們此時正在監聽lo上的6666端口的數據包。
然后我們用客戶端去連接它：
1 ~/codeDir/phpCode/hyperf-skeleton # nc 127.0.0.1 6666
此時服務端會打印出消息：
~/codeDir/phpCode/hyperf-skeleton # php server.php string(17) "Client: Connect 1"
tcpdump的輸出信息如下：
1 01:48:40.178439 IP localhost.33933 > localhost.6666: Flags [S], seq 43162537, win 43690, options [mss 65495,sackOK,TS val 9833698 ecr 0,nop,wscale 7], length 0 2 01:48:40.178484 IP localhost.6666 > localhost.33933: Flags [S.], seq 1327460565, ack 43162538, win 43690, options [mss 65495,sackOK,TS val 9833698 ecr 9833698,nop,wscale 7], length 0 3 01:48:40.178519 IP localhost.33933 > localhost.6666: Flags [.], ack 1, win 342, options [nop,nop,TS val 9833698 ecr 9833698], length 0 4 01:48:44.229926 IP localhost.6666 > localhost.33933: Flags [.], ack 1, win 342, options [nop,nop,TS val 9834104 ecr 9833698], length 0 5 01:48:44.229951 IP localhost.33933 > localhost.6666: Flags [.], ack 1, win 342, options [nop,nop,TS val 9834104 ecr 9833698], length 0 6 01:48:44.229926 IP localhost.6666 > localhost.33933: Flags [.], ack 1, win 342, options [nop,nop,TS val 9834104 ecr 9833698], length 0 7 01:48:44.229951 IP localhost.33933 > localhost.6666: Flags [.], ack 1, win 342, options [nop,nop,TS val 9834104 ecr 9833698], length 0 8 01:48:44.229926 IP localhost.6666 > localhost.33933: Flags [.], ack 1, win 342, options [nop,nop,TS val 9834104 ecr 9833698], length 0 9 // 省略了其他的輸出
我們會發現最開始的時候，會打印三次握手的包：
01:48:40.178439 IP localhost.33933 > localhost.6666: Flags [S], seq 43162537, win 43690, options [mss 65495,sackOK,TS val 9833698 ecr 0,nop,wscale 7], length 0 01:48:40.178484 IP localhost.6666 > localhost.33933: Flags [S.], seq 1327460565, ack 43162538, win 43690, options [mss 65495,sackOK,TS val 9833698 ecr 9833698,nop,wscale 7], length 0 01:48:40.178519 IP localhost.33933 > localhost.6666: Flags [.], ack 1, win 342, options [nop,nop,TS val 9833698 ecr 9833698], length 0
然后，停留了4s沒有任何包的輸出。
之后，每隔1s左右就會打印出一組：
1 01:52:54.359341 IP localhost.6666 > localhost.43101: Flags [.], ack 1, win 342, options [nop,nop,TS val 9859144 ecr 9858736], length 0 2 01:52:54.359377 IP localhost.43101 > localhost.6666: Flags [.], ack 1, win 342, options [nop,nop,TS val 9859144 ecr 9855887], length 0
其實這就是我們配置的策略：
1 'tcp_keepinterval' => 1, // 1s探測一次 2 'tcp_keepcount' => 5, // 探測的次數，超過5次后還沒有回包close此連接
因為我們操作系統底層會自動的給客戶端回ack，所以這個連接不會在5次探測后被關閉。操作系統底層會持續不斷的發送這樣的一組包：
1 01:52:54.359341 IP localhost.6666 > localhost.43101: Flags [.], ack 1, win 342, options [nop,nop,TS val 9859144 ecr 9858736], length 0 2 01:52:54.359377 IP localhost.43101 > localhost.6666: Flags [.], ack 1, win 342, options [nop,nop,TS val 9859144 ecr 9855887], length 0
如果我們要測試5次探測后關閉這個連接，可以禁掉6666端口的包：
1 ~/codeDir/phpCode/hyperf-skeleton # iptables -A INPUT -p tcp --dport 6666 -j DROP
這樣會把所有從6666端口進來的包給禁掉，自然，服務器就接收不到從客戶端那一邊發來的ack包了。
然后服務器過5秒就會打印出close（服務端主動的調用了close方法，給客戶端發送了FIN包）：
1 ~/codeDir/phpCode/hyperf-skeleton # php server.php 2 string(17) "Client: Connect 1" 3 string(10) "close fd 1"
我們恢復一下iptables的規則：
1 ~/codeDir/phpCode # iptables -D INPUT -p tcp -m tcp --dport 6666 -j DROP
即把我們設置的規則給刪除了。
通過tcp_keepalive的方式實現心跳的功能，優點是簡單，不要寫代碼就可以完成這個功能，並且發送的心跳包小。缺點是依賴於系統的網絡環境，必須保證服務器和客戶端都實現了這樣的功能，需要客戶端配合發心跳包。還有一個更為嚴重的缺點是如果客戶端和服務器不是直連的，而是通過代理來進行連接的，例如socks5代理，它只會轉發應用層的包，不會轉發更為底層的tcp探測包，那這個心跳功能就失效了。
所以，Swoole就提供了其他的解決方案，一組檢測死連接的配置。
1 'heartbeat_check_interval' => 1, // 1s探測一次 2 'heartbeat_idle_time' => 5, // 5s未發送數據包就close此連接
swoole實現的heartbeat
我們來測試一下：
1 <?php 2 3 $server = new \Swoole\Server('127.0.0.1', 6666, SWOOLE_PROCESS); 4 5 $server->set([ 6 'worker_num' => 1, 7 'heartbeat_check_interval' => 1, // 1s探測一次 8 'heartbeat_idle_time' => 5, // 5s未發送數據包就close此連接 9 ]); 10 11 $server->on('connect', function ($server, $fd) { 12 var_dump("Client: Connect $fd"); 13 }); 14 15 $server->on('receive', function ($server, $fd, $reactor_id, $data) { 16 var_dump($data); 17 }); 18 19 $server->on('close', function ($server, $fd) { 20 var_dump("close fd $fd"); 21 }); 22 23 $server->start();
然后啟動服務器：
1 ~/codeDir/phpCode/hyperf-skeleton # php server.php
然后啟動tcpdump：
1 ~/codeDir/phpCode # tcpdump -i lo port 6666 2 tcpdump: verbose output suppressed, use -v or -vv for full protocol decode 3 listening on lo, link-type EN10MB (Ethernet), capture size 262144 bytes
然后再啟動客戶端：
1 ~/codeDir/phpCode/hyperf-skeleton # nc 127.0.0.1 6666
此時服務器端打印：
1 ~/codeDir/phpCode/hyperf-skeleton # php server.php 2 string(17) "Client: Connect 1"
然后tcpdump打印：
1 02:48:32.516093 IP localhost.42123 > localhost.6666: Flags [S], seq 1088388248, win 43690, options [mss 65495,sackOK,TS val 10193342 ecr 0,nop,wscale 7], length 0 2 02:48:32.516133 IP localhost.6666 > localhost.42123: Flags [S.], seq 80508236, ack 1088388249, win 43690, options [mss 65495,sackOK,TS val 10193342 ecr 10193342,nop,wscale 7], length 0 3 02:48:32.516156 IP localhost.42123 > localhost.6666: Flags [.], ack 1, win 342, options [nop,nop,TS val 10193342 ecr 10193342], length 0
這是三次握手信息。
然后過了5s后，tcpdump會打印出：
1 02:48:36.985027 IP localhost.6666 > localhost.42123: Flags [F.], seq 1, ack 1, win 342, options [nop,nop,TS val 10193789 ecr 10193342], length 0 2 02:48:36.992172 IP localhost.42123 > localhost.6666: Flags [.], ack 2, win 342, options [nop,nop,TS val 10193790 ecr 10193789], length 0
也就是服務端發送了FIN包。因為客戶端沒有發送數據，所以Swoole關閉了連接。
然后服務器端會打印：
1 ~/codeDir/phpCode/hyperf-skeleton # php server.php 2 string(17) "Client: Connect 1" 3 string(10) "close fd 1"
所以，heartbeat和tcp keepalive還是有一定的區別的，tcp keepalive有保活連接的功能，但是heartbeat存粹是檢測沒有數據的連接，然后關閉它，並且只可以在服務端這邊配置，如果需要保活，也可以讓客戶端配合發送心跳。
如果我們不想讓服務端close掉連接，那么就得在應用層里面不斷的發送數據包來進行保活，例如我在nc客戶端里面不斷的發送包：
1 ~/codeDir/phpCode/hyperf-skeleton # nc 127.0.0.1 6666 2 ping 3 ping 4 ping 5 ping 6 ping 7 ping 8 ping 9 ping 10 ping
我發送了9個ping包給服務器，tcpdump的輸出如下：
1 // 省略了三次握手的包 2 02:57:53.697363 IP localhost.44195 > localhost.6666: Flags [P.], seq 1:6, ack 1, win 342, options [nop,nop,TS val 10249525 ecr 10249307], length 5 3 02:57:53.697390 IP localhost.6666 > localhost.44195: Flags [.], ack 6, win 342, options [nop,nop,TS val 10249525 ecr 10249525], length 0 4 02:57:55.309532 IP localhost.44195 > localhost.6666: Flags [P.], seq 6:11, ack 1, win 342, options [nop,nop,TS val 10249686 ecr 10249525], length 5 5 02:57:55.309576 IP localhost.6666 > localhost.44195: Flags [.], ack 11, win 342, options [nop,nop,TS val 10249686 ecr 10249686], length 0 6 02:57:58.395206 IP localhost.44195 > localhost.6666: Flags [P.], seq 11:16, ack 1, win 342, options [nop,nop,TS val 10249994 ecr 10249686], length 5 7 02:57:58.395239 IP localhost.6666 > localhost.44195: Flags [.], ack 16, win 342, options [nop,nop,TS val 10249994 ecr 10249994], length 0 8 02:58:01.858094 IP localhost.44195 > localhost.6666: Flags [P.], seq 16:21, ack 1, win 342, options [nop,nop,TS val 10250341 ecr 10249994], length 5 9 02:58:01.858126 IP localhost.6666 > localhost.44195: Flags [.], ack 21, win 342, options [nop,nop,TS val 10250341 ecr 10250341], length 0 10 02:58:04.132584 IP localhost.44195 > localhost.6666: Flags [P.], seq 21:26, ack 1, win 342, options [nop,nop,TS val 10250568 ecr 10250341], length 5 11 02:58:04.132609 IP localhost.6666 > localhost.44195: Flags [.], ack 26, win 342, options [nop,nop,TS val 10250568 ecr 10250568], length 0 12 02:58:05.895704 IP localhost.44195 > localhost.6666: Flags [P.], seq 26:31, ack 1, win 342, options [nop,nop,TS val 10250744 ecr 10250568], length 5 13 02:58:05.895728 IP localhost.6666 > localhost.44195: Flags [.], ack 31, win 342, options [nop,nop,TS val 10250744 ecr 10250744], length 0 14 02:58:07.150265 IP localhost.44195 > localhost.6666: Flags [P.], seq 31:36, ack 1, win 342, options [nop,nop,TS val 10250870 ecr 10250744], length 5 15 02:58:07.150288 IP localhost.6666 > localhost.44195: Flags [.], ack 36, win 342, options [nop,nop,TS val 10250870 ecr 10250870], length 0 16 02:58:08.349124 IP localhost.44195 > localhost.6666: Flags [P.], seq 36:41, ack 1, win 342, options [nop,nop,TS val 10250990 ecr 10250870], length 5 17 02:58:08.349156 IP localhost.6666 > localhost.44195: Flags [.], ack 41, win 342, options [nop,nop,TS val 10250990 ecr 10250990], length 0 18 02:58:09.906223 IP localhost.44195 > localhost.6666: Flags [P.], seq 41:46, ack 1, win 342, options [nop,nop,TS val 10251145 ecr 10250990], length 5 19 02:58:09.906247 IP localhost.6666 > localhost.44195: Flags [.], ack 46, win 342, options [nop,nop,TS val 10251145 ecr 10251145], length 0
有9組數據包的發送。（這里的Flags [P.]代表Push的含義）
此時服務器還沒有close掉連接，實現了客戶端保活連接的功能。然后我們停止發送ping，過了5秒后tcpdump就會輸出一組：
02:58:14.811761 IP localhost.6666 > localhost.44195: Flags [F.], seq 1, ack 46, win 342, options [nop,nop,TS val 10251636 ecr 10251145], length 0
02:58:14.816420 IP localhost.44195 > localhost.6666: Flags [.], ack 2, win 342, options [nop,nop,TS val 10251637 ecr 10251636], length 0
服務端那邊發送了FIN包，說明服務端close掉了連接。服務端的輸出如下：
1 ~/codeDir/phpCode/hyperf-skeleton # php server.php 2 string(17) "Client: Connect 1" 3 string(5) "ping 4 " 5 string(5) "ping 6 " 7 string(5) "ping 8 " 9 string(5) "ping 10 " 11 string(5) "ping 12 " 13 string(5) "ping 14 " 15 string(5) "ping 16 " 17 string(5) "ping 18 " 19 string(5) "ping 20 " 21 string(10) "close fd 1"
然后我們在客戶端那邊ctrl + c來關閉連接：
1 ~/codeDir/phpCode/hyperf-skeleton # nc 127.0.0.1 6666 2 ping 3 ping 4 ping 5 ping 6 ping 7 ping 8 ping 9 ping 10 ping 11 ^Cpunt! 12 13 ~/codeDir/phpCode/hyperf-skeleton #
此時，tcpdump的輸出如下：
1 03:03:02.257667 IP localhost.44195 > localhost.6666: Flags [F.], seq 46, ack 2, win 342, options [nop,nop,TS val 10280414 ecr 10251636], length 0 2 03:03:02.257734 IP localhost.6666 > localhost.44195: Flags [R], seq 2678621620, win 0, length 0
應用層心跳
1、制定ping/pong協議（mysql等自帶ping協議）
2、客戶端靈活的發送ping心跳包
3、服務端OnRecive檢查可用性回復pong
例如：
1 $server->on('receive', function (\Swoole\Server $server, $fd, $reactor_id, $data) 2 { 3 if ($data == 'ping') 4 { 5 checkDB(); 6 checkServiceA(); 7 checkRedis(); 8 $server->send('pong'); 9 } 10 });
結論
1、tcp的keepalive最簡單，但是有兼容性問題，不夠靈活
2、swoole提供的keepalive最實用，但是需要客戶端配合，復雜度適中
3、應用層的keepalive最靈活但是最麻煩