聊聊nginx的keepalive_time参数

序

本文主要研究一下nginx的keepalive_time参数

keepalive_time

Syntax:    keepalive_time time;
Default:    
keepalive_time 1h;
Context:    http, server, location
This directive appeared in version 1.19.10.

nginx的1.19.10版本新增了keepalive_time参数，用于限制一个keep-alive连接处理请求的最长时间。当达到这个时间后，连接会在后续请求处理完成后关闭。

ngx_http_core_module

nginx/src/http/ngx_http_core_module.c

void
ngx_http_update_location_config(ngx_http_request_t *r)
{
    ngx_http_core_loc_conf_t  *clcf;

    //......

    if (r->keepalive) {
        if (clcf->keepalive_timeout == 0) {
            r->keepalive = 0;

        } else if (r->connection->requests >= clcf->keepalive_requests) {
            r->keepalive = 0;

        } else if (ngx_current_msec - r->connection->start_time
                   > clcf->keepalive_time)
        {
            r->keepalive = 0;

        } else if (r->headers_in.msie6
                   && r->method == NGX_HTTP_POST
                   && (clcf->keepalive_disable
                       & NGX_HTTP_KEEPALIVE_DISABLE_MSIE6))
        {
            /*
             * MSIE may wait for some time if an response for
             * a POST request was sent over a keepalive connection
             */
            r->keepalive = 0;

        } else if (r->headers_in.safari
                   && (clcf->keepalive_disable
                       & NGX_HTTP_KEEPALIVE_DISABLE_SAFARI))
        {
            /*
             * Safari may send a POST request to a closed keepalive
             * connection and may stall for some time, see
             *     https://bugs.webkit.org/show_bug.cgi?id=5760
             */
            r->keepalive = 0;
        }
    }

    //......
}    

ngx_http_core_module的ngx_http_update_location_config方法在开启keepalive时会判断connection的存活时间，若大于keepalive_time则关闭keepalive(ngx_current_msec - r->connection->start_time > clcf->keepalive_time)

ngx_http_core_keepalive

nginx/src/http/ngx_http_core_module.c

static char *
ngx_http_core_keepalive(ngx_conf_t *cf, ngx_command_t *cmd, void *conf)
{
    ngx_http_core_loc_conf_t *clcf = conf;

    ngx_str_t  *value;

    if (clcf->keepalive_timeout != NGX_CONF_UNSET_MSEC) {
        return "is duplicate";
    }

    value = cf->args->elts;

    clcf->keepalive_timeout = ngx_parse_time(&value[1], 0);

    if (clcf->keepalive_timeout == (ngx_msec_t) NGX_ERROR) {
        return "invalid value";
    }

    if (cf->args->nelts == 2) {
        return NGX_CONF_OK;
    }

    clcf->keepalive_header = ngx_parse_time(&value[2], 1);

    if (clcf->keepalive_header == (time_t) NGX_ERROR) {
        return "invalid value";
    }

    return NGX_CONF_OK;
}

ngx_http_core_module的ngx_http_core_keepalive方法会解析nginx配置文件的keepalive_timeout配置，第一个参数为keepalive_timeout参数，第二参数为header_timeout

ngx_http_header_filter_module

nginx/src/http/ngx_http_header_filter_module.c

static ngx_int_t
ngx_http_header_filter(ngx_http_request_t *r)
{
    u_char                    *p;
    size_t                     len;
    ngx_str_t                  host, *status_line;
    ngx_buf_t                 *b;
    ngx_uint_t                 status, i, port;
    ngx_chain_t                out;
    ngx_list_part_t           *part;
    ngx_table_elt_t           *header;
    ngx_connection_t          *c;
    ngx_http_core_loc_conf_t  *clcf;
    ngx_http_core_srv_conf_t  *cscf;
    u_char                     addr[NGX_SOCKADDR_STRLEN];

    if (r->header_sent) {
        return NGX_OK;
    }

    //......

    if (r->headers_out.status == NGX_HTTP_SWITCHING_PROTOCOLS) {
        b->last = ngx_cpymem(b->last, "Connection: upgrade" CRLF,
                             sizeof("Connection: upgrade" CRLF) - 1);

    } else if (r->keepalive) {
        b->last = ngx_cpymem(b->last, "Connection: keep-alive" CRLF,
                             sizeof("Connection: keep-alive" CRLF) - 1);

        if (clcf->keepalive_header) {
            b->last = ngx_sprintf(b->last, "Keep-Alive: timeout=%T" CRLF,
                                  clcf->keepalive_header);
        }

    } else {
        b->last = ngx_cpymem(b->last, "Connection: close" CRLF,
                             sizeof("Connection: close" CRLF) - 1);
    }

    //......
}    

ngx_http_header_filter_module的ngx_http_header_filter方法在开启keepalive的时候会写入Connection: keep-alive，若keepalive_header的值大于0则写入Keep-Alive: timeout=%T，可以看到这个值是固定的

ngx_http_set_keepalive

nginx/src/http/ngx_http_request.c

static void
ngx_http_set_keepalive(ngx_http_request_t *r)
{
    int                        tcp_nodelay;
    ngx_buf_t                 *b, *f;
    ngx_chain_t               *cl, *ln;
    ngx_event_t               *rev, *wev;
    ngx_connection_t          *c;
    ngx_http_connection_t     *hc;
    ngx_http_core_loc_conf_t  *clcf;

    //......

    wev = c->write;
    wev->handler = ngx_http_empty_handler;

    if (b->pos < b->last) {

        ngx_log_debug0(NGX_LOG_DEBUG_HTTP, c->log, 0, "pipelined request");

        c->log->action = "reading client pipelined request line";

        r = ngx_http_create_request(c);
        if (r == NULL) {
            ngx_http_close_connection(c);
            return;
        }

        r->pipeline = 1;

        c->data = r;

        c->sent = 0;
        c->destroyed = 0;
        c->pipeline = 1;

        if (rev->timer_set) {
            ngx_del_timer(rev);
        }

        rev->handler = ngx_http_process_request_line;
        ngx_post_event(rev, &ngx_posted_events);
        return;
    }

    //......

    rev->handler = ngx_http_keepalive_handler;

    //......

    c->idle = 1;
    ngx_reusable_connection(c, 1);

    ngx_add_timer(rev, clcf->keepalive_timeout);

    if (rev->ready) {
        ngx_post_event(rev, &ngx_posted_events);
    }    
}    

ngx_http_request的ngx_http_set_keepalive方法，在b->pos < b->last会尝试读取request line然后执行ngx_http_create_request，若能读到数据则判断是否有timer，有则执行ngx_del_timer(rev)删除timer，然后返回；若进入keepalive逻辑，则会通过ngx_add_timer添加一个定时事件，在keepalive_timeout之后触发

ngx_http_keepalive_handler

nginx/src/http/ngx_http_request.c

static void
ngx_http_keepalive_handler(ngx_event_t *rev)
{
    size_t             size;
    ssize_t            n;
    ngx_buf_t         *b;
    ngx_connection_t  *c;

    c = rev->data;

    ngx_log_debug0(NGX_LOG_DEBUG_HTTP, c->log, 0, "http keepalive handler");

    if (rev->timedout || c->close) {
        ngx_http_close_connection(c);
        return;
    }

#if (NGX_HAVE_KQUEUE)

    if (ngx_event_flags & NGX_USE_KQUEUE_EVENT) {
        if (rev->pending_eof) {
            c->log->handler = NULL;
            ngx_log_error(NGX_LOG_INFO, c->log, rev->kq_errno,
                          "kevent() reported that client %V closed "
                          "keepalive connection", &c->addr_text);
#if (NGX_HTTP_SSL)
            if (c->ssl) {
                c->ssl->no_send_shutdown = 1;
            }
#endif
            ngx_http_close_connection(c);
            return;
        }
    }

#endif

    b = c->buffer;
    size = b->end - b->start;

    if (b->pos == NULL) {

        /*
         * The c->buffer's memory was freed by ngx_http_set_keepalive().
         * However, the c->buffer->start and c->buffer->end were not changed
         * to keep the buffer size.
         */

        b->pos = ngx_palloc(c->pool, size);
        if (b->pos == NULL) {
            ngx_http_close_connection(c);
            return;
        }

        b->start = b->pos;
        b->last = b->pos;
        b->end = b->pos + size;
    }

    /*
     * MSIE closes a keepalive connection with RST flag
     * so we ignore ECONNRESET here.
     */

    c->log_error = NGX_ERROR_IGNORE_ECONNRESET;
    ngx_set_socket_errno(0);

    n = c->recv(c, b->last, size);
    c->log_error = NGX_ERROR_INFO;

    if (n == NGX_AGAIN) {
        if (ngx_handle_read_event(rev, 0) != NGX_OK) {
            ngx_http_close_connection(c);
            return;
        }

        /*
         * Like ngx_http_set_keepalive() we are trying to not hold
         * c->buffer's memory for a keepalive connection.
         */

        if (ngx_pfree(c->pool, b->start) == NGX_OK) {

            /*
             * the special note that c->buffer's memory was freed
             */

            b->pos = NULL;
        }

        return;
    }

    if (n == NGX_ERROR) {
        ngx_http_close_connection(c);
        return;
    }

    c->log->handler = NULL;

    if (n == 0) {
        ngx_log_error(NGX_LOG_INFO, c->log, ngx_socket_errno,
                      "client %V closed keepalive connection", &c->addr_text);
        ngx_http_close_connection(c);
        return;
    }

    b->last += n;

    c->log->handler = ngx_http_log_error;
    c->log->action = "reading client request line";

    c->idle = 0;
    ngx_reusable_connection(c, 0);

    c->data = ngx_http_create_request(c);
    if (c->data == NULL) {
        ngx_http_close_connection(c);
        return;
    }

    c->sent = 0;
    c->destroyed = 0;

    ngx_del_timer(rev);

    rev->handler = ngx_http_process_request_line;
    ngx_http_process_request_line(rev);
}

ngx_http_request的ngx_http_keepalive_handler会在rev->timedout || c->close的时候执行ngx_http_close_connection然后返回，若还能读到请求数据则执行ngx_del_timer(rev)删除定时任务

小结

nginx的1.19.10版本新增了keepalive_time参数(默认1h)，用于限制一个keep-alive连接处理请求的最长时间(即指定connection的最大存活时间)，当达到这个时间后，连接会在后续请求处理完成后关闭。而keepalive_timeout参数(默认75s)则是用于指定connection最大的空闲时间，nginx内部有会给该连接设定一个timer，在keepalive_timeout之后触发，若连接还是空闲则关闭连接。

doc

• keepalive_time
• What's the difference between Nginx 'keepalive_time' and 'keepalive_timeout'?