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;}
#endifngx_http_close_connection(c);return;}}#endifb = 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’?