每秒测量出站请求？

Question

我有一个Web应用程序，该应用程序使用ActiveResource与另一台具有连接速率限制的服务器通信。我很好奇如何才能最好地从运行我的Web应用程序的主机上进行监视，即从服务器上linux上的bash提示符下，如何测量我的计算机每秒向另一台计算机发出的出站请求？

我正在寻找给定接口，主机名和/或它们的某种组合的Linux单行程序，它告诉我与该服务器的连接速率。我已经接近使用tc和iftop之类的工具，但是这些工具报告的是所传输的数据量，而不是所建立的连接……所以它并不是我所要寻找的。我很想看类似的东西：

---

$ awesometool --host thetargethost.com --interface eth0 --interval 5

收集统计数据…

接口eth0上针对targethost.com的每秒请求报告

平均：23请求/秒最小值：12请求/秒最大值39请求/秒

抽取了5个样本

---

谁能指出我一个人？

Answer 1

tcpdump(8)可以提供非常相似的东西；搜索带有设置标志的 TCP 数据包，以捕获三向握手中发往其他对等方的SYN第一个数据包：

$ sudo tcpdump -c 10 -i eth0 "tcp[tcpflags] & (tcp-syn) != 0 and dst 192.168.0.1"
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
18:26:24.800308 IP haig.59419 > 192.168.0.1.telnet: Flags [S], seq 3197302320, win 14600, options [mss 1460,sackOK,TS val 19460844 ecr 0,nop,wscale 7], length 0
...
18:26:27.420132 IP haig.59428 > 192.168.0.1.telnet: Flags [S], seq 1238498237, win 14600, options [mss 1460,sackOK,TS val 19461106 ecr 0,nop,wscale 7], length 0
10 packets captured
10 packets received by filter
0 packets dropped by kernel

您可以使用/usr/bin/timeshell 的time内置功能，或者对输出中的时间戳进行一些算术，以获得每秒的平均速率。（使用十多个包——这只是为了演示。）

更新

我编写了一个小程序来运行tcpdump(8)，对数据包进行计数，并报告在指定的时间间隔内发送了多少数据包：

# ./counter --host 192.168.0.1 --interface eth0 --interval 3
2 requests in 3 seconds; average 0.67 req/seq
20 requests in 3 seconds; average 6.67 req/seq
19 requests in 3 seconds; average 6.33 req/seq
19 requests in 3 seconds; average 6.33 req/seq
^C
# ./counter --host 192.168.0.1 --interface eth0 --interval 5
30 requests in 5 seconds; average 6.00 req/seq
20 requests in 5 seconds; average 4.00 req/seq
1176 requests in 5 seconds; average 235.20 req/seq
1414 requests in 5 seconds; average 282.80 req/seq
0 requests in 5 seconds; average 0.00 req/seq
^C

因为它要求tcpdump(8)使用行缓冲输出，所以我有点担心它可能不会扩展到每秒超过 200-300 个请求，至少在我的硬件上是这样。但是如果没有行缓冲输出，tcpdump(8)则将等到其输出缓冲区（请参阅setvbuf(3)详细信息）已满后再发送任何输出，从而导致极其不稳定的结果。

但如果您的连接率不是那么高，这可能会满足您的需要。如果您的连接率较高，那么最好忽略这个小技巧——我觉得它可能iptables(8)可以对流进行计数。

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <getopt.h>
#include <signal.h>
#include <errno.h>
#include <fcntl.h>
#include <sys/types.h>

#define CMDLEN 1024
#define TCPDUMPLEN 4096

int show_stats;
long counter;

void alarm_handler(int signum)
{
    show_stats = 1;
}

void install_handler(void)
{
    struct sigaction sa;

    memset(&sa, 0, sizeof(sa));

    sigemptyset(&sa.sa_mask);
    sa.sa_handler = &alarm_handler;
    if (sigaction(SIGALRM, &sa, NULL) == -1) {
        perror("Can't install alarm handler");
        exit(1);
    }
}

int count_lines(char *p, int bytes)
{
    int counter = 0;
    char *i;
    for (i=p; i < p+bytes ; i++) {
        if (*i == '\n')
            counter++;
    }
    return counter;
}

int spawn_tcpdump(char *host, char *interface)
{
    int fd[2];
    pid_t child;

    if (pipe(fd) == -1) {
        perror("Can't create pipes");
        exit(1);
    }

    child = fork();

    if (child == -1) {
        perror("Can't fork(2) for tcpdump");
        exit(1);
    }

    if (child == 0) {
        int null;
        int len;
        char syn_and_dst[CMDLEN];

        len = snprintf(syn_and_dst, CMDLEN, "tcp[tcpflags] & (tcp-syn) != 0 and dst %s", host);

        if (len > CMDLEN) {
            perror("host argument too long");
            exit(1);
        }

        /* child writes into pipe */
        close(fd[0]);
        dup2(fd[1], STDOUT_FILENO);

        /* throw away first two lines of tcpdump output */
        null = open("/dev/null", O_WRONLY);

        if (null == -1) {
            perror("Can't open /dev/null");
            exit(1);
        }

        dup2(null, STDERR_FILENO);

        execl("/usr/sbin/tcpdump", "tcpdump", "-l", "-n", "-s 96", "-i", interface, syn_and_dst, (char *) NULL);
        /* can't reach */
        perror("Cannot execute tcpdump");
        exit(1); 
    } else {
        /* parent reads from pipe */
        close(fd[1]);
        return fd[0];
    }
}

int main(int argc, char *argv[])
{
    int tcpdump;
    char *host;
    char *interface;
    long interval;


    while (1) {
        int option_index;
        int c;

        static struct option opts[] = {
            {"host", required_argument, NULL, 'h'},
            {"interface", required_argument, NULL, 'i'},
            {"interval", required_argument, NULL, 'n'},
            {0, 0, 0, 0},
        };

        c = getopt_long(argc, argv, "", opts, &option_index);

        if (c == -1)
            break;

        switch (c) {
            case 'h':
                host = strdup(optarg);
                break;
            case 'i':
                interface = strdup(optarg);
                break;
            case 'n': {
                    char *endptr;
                    interval = strtol(optarg, &endptr, 10);
                    if (!(optarg[0] != '\0' && endptr[0] == '\0')) {
                        fprintf(stderr, "Expected integer; invalid"
                                " input '%s'\n", optarg);
                        exit(1);
                    }
                }
                break;
            default:
                fprintf(stderr, "Option parsing error\n");
                exit(1);
        }

    }

    if (optind < argc) {
        fprintf(stderr, "unexpected arguments: ");
        while (optind < argc) {
            fprintf(stderr, "%s ", argv[optind++]);
        }
        fprintf(stderr, "\n");
    }

    tcpdump = spawn_tcpdump(host, interface);

    install_handler();
    alarm(interval);

    while(1) {
        if (show_stats) {
            printf("%ld requests in %ld seconds; average %2.2f req/seq\n",
                    counter, interval, (double)counter / (double)interval);
            counter = 0;
            show_stats = 0;
            alarm(interval);
        } else {
            char buffer[TCPDUMPLEN];
            int ret;

            memset(buffer, 0, TCPDUMPLEN);
            ret = read(tcpdump, buffer, TCPDUMPLEN);
            if (ret == -1 && errno == EINTR) {
                /* nop */
            } else if (ret == -1) {
                perror("read");
                exit(1);
            } else {
                counter += count_lines(buffer, ret);
            }
        }
    }

    exit(0);
}