Upstream keepalive: keepalive_timeout directive. The directive configures maximum time a connection can be kept in the cache. By configuring a time which is smaller than the corresponding timeout on the backend side one can avoid the race between closing a connection by the backend and nginx trying to use the same connection to send a request at the same time.

/*
 * Copyright (C) Igor Sysoev
 * Copyright (C) Nginx, Inc.
 */


#ifndef _NGX_CRYPT_H_INCLUDED_
#define _NGX_CRYPT_H_INCLUDED_


#include <ngx_config.h>
#include <ngx_core.h>


ngx_int_t ngx_crypt(ngx_pool_t *pool, u_char *key, u_char *salt,
    u_char **encrypted);


#endif /* _NGX_CRYPT_H_INCLUDED_ */