月度归档:2017年08月

LVS、Nginx 及 HAProxy 的工作原理

当前大多数的互联网系统都使用了服务器集群技术,集群是将相同服务部署在多台服务器上构成一个集群整体对外提供服务,这些集群可以是 Web 应用服务器集群,也可以是数据库服务器集群,还可以是分布式缓存服务器集群等等。

在实际应用中,在 Web 服务器集群之前总会有一台负载均衡服务器,负载均衡设备的任务就是作为 Web 服务器流量的入口,挑选最合适的一台 Web 服务器,将客户端的请求转发给它处理,实现客户端到真实服务端的透明转发。

最近几年很火的「云计算」以及分布式架构,本质上也是将后端服务器作为计算资源、存储资源,由某台管理服务器封装成一个服务对外提供,客户端不需要关心真正提供服务的是哪台机器,在它看来,就好像它面对的是一台拥有近乎无限能力的服务器,而本质上,真正提供服务的,是后端的集群。 继续阅读

SSH服务的几个超时参数 以及 类似DDOS攻击的方法

背景

sshd是Linux的一个常用的网络连接的服务,通常被用来远程连接,管理服务器。

一般我们很少去配置sshd,本文要给大家分享几个sshd的参数,有超时参数,有触发拒绝连接的参数等等。

如果你哪天遇到类似的问题,也行能帮助你找到问题的根源。 继续阅读

How to:Python

1、django.core.exceptions.ImproperlyConfigured: Requested setting DEBUG, but settings are not configured.

You must either define the environment variable DJANGO_SETTINGS_MODULE or call settings.configure() before accessing settings.

>>> from django.conf import settings
>>> settings.configure()
>>> from django.test.utils import setup_test_environment
>>> setup_test_environment()

How to setup an SFTP server on CentOS

This tutorial explains how to setup and use an SFTP server on CentOS. Before I start, let me explain what actually SFTP represents and what it is used for. Currently, most people know that we can use normal FTP for transferring, downloading or uploading data from a server to client or client to server. But this protocol is getting hacked easily (if TLS is not used) by anonymous intruders as it the ports are widely open to anyone. Therefore, SFTP has been introduced to as another alternative to meet the main purpose to strengthen the security level.

SFTP stands for SSH File Transfer Protocol or Secure File Transfer Protocol. It uses a separate protocol packaged with SSH to provide a secure connection. 继续阅读

Linux: TMOUT To Automatically Log Users Out

How do I auto Logout my shell user in Linux after certain minutes of inactivity?

Linux bash shell allows you to define the TMOUT environment variable. Set TMOUT to automatically log users out after a period of inactivity. The value is defined in seconds. For example,

export TMOUT=120

export TMOUT=120

The above command will implement a 2 minute idle time-out for the default /bin/bash shell. You can edit your ~/.bash_profile or /etc/profile file as follows to define a 5 minute idle time out:

# set a 5 min timeout policy for bash shell
TMOUT=300
readonly TMOUT
export TMOUT

# set a 5 min timeout policy for bash shell TMOUT=300 readonly TMOUT export TMOUT

Save and close the file. The readonly command is used to make variables and functions readonly i.e. you user cannot change the value of variable called TMOUT.

How Do I Disable TMOUT?

To disable auto-logout, just set the TMOUT to zero or unset it as follows:
$ export TMOUT=0
or
$ unset TMOUT
Please note that readonly variable can only be disabled by root in /etc/profile or ~/.bash_profile.

A Note About TCSH SHELL and OpenSSH Server/Client

SSH allows administrators to set an idle timeout interval in /etc/ssh/sshd_config file. TCSH user should use autologout variable. Please see our previous FAQ “Linux / UNIX Automatically Log BASH / TCSH / SSH Users Out After a Period of Inactivity” for more information.

use MySQL on Django with Python3.6

My environment: Windows 10, Python 3.6, Django 1.11.4., PyMySQL 0.6.1, MySQL Server 5.7 on Windows

How to make it work:

  1. Install PyMySQL version 0.7.11 (https://github.com/PyMySQL/PyMySQL/): you can install it either by using pip, i.e. : pip install PyMySQL or by manually downloading the package; there is a good documentation on their website on how to do that.
  2. Open your Django App __init__.py and paste the following lines:
    import pymysql
    pymysql.install_as_MySQLdb() 
    
  3. Now, open settings.py and make sure your DATABASE property looks like this:
    DATABASES = {
       'default': {
           'ENGINE': 'django.db.backends.mysql',
           'NAME': 'mydb',
           'USER': 'dbuser',
           'PASSWORD': 'dbpassword',
           'HOST': 'dbhost',
           'PORT': '3306'
        }
    }
    
  4. That’s it, you should be able to execute python manage.py syncdb to init your MySQL DB; see the sample output below:
    Creating tables ...
    Creating table django_admin_log
    Creating table auth_permission
    Creating table auth_group_permissions
    ...
    ...
    Creating table socialaccount_socialtoken
    
    You just installed Django's auth system, which means you don't have any superusers defined.
    ...
    
  5. you should be able to execute python manage.py migrate to creates any necessary database tables according
    to the database settings in your mysite/settings.py file and the database migrations shipped with the app; see the sample output below:

    
    Operations to perform:
      Apply all migrations: admin, auth, contenttypes, sessions
    Running migrations:
      Applying contenttypes.0001_initial... OK
      Applying auth.0001_initial... OK
      Applying admin.0001_initial... OK
      Applying admin.0002_logentry_remove_auto_add... OK
      Applying contenttypes.0002_remove_content_type_name... OK
      Applying auth.0002_alter_permission_name_max_length... OK
      Applying auth.0003_alter_user_email_max_length... OK
      Applying auth.0004_alter_user_username_opts... OK
      Applying auth.0005_alter_user_last_login_null... OK
      Applying auth.0006_require_contenttypes_0002... OK
      Applying auth.0007_alter_validators_add_error_messages... OK
      Applying auth.0008_alter_user_username_max_length... OK
      Applying sessions.0001_initial... OK
    

apache禁止访问文件或目录执行权限、禁止运行脚本PHP文件的设置方法

我们来看俩段通常对上传目录设置无权限的列子,配置如下:

代码如下:

<Directory “/var/www/upload”>
<FilesMatch “.php”>
Order Allow,Deny
Deny from all
</FilesMatch>
</Directory>

这些配置表面上看起来是没什么问题的,确实在windows下可以这么说。
但是linux就不同了,大家都是知道的linux操作系统是区分大小写的,这里如果换成大写后缀名*.phP一类就pass了 继续阅读

File System Redirector

The %windir%\System32 directory is reserved for 64-bit applications. Most DLL file names were not changed when 64-bit versions of the DLLs were created, so 32-bit versions of the DLLs are stored in a different directory. WOW64 hides this difference by using a file system redirector.

In most cases, whenever a 32-bit application attempts to access %windir%\System32, the access is redirected to %windir%\SysWOW64. Access to %windir%\lastgood\system32 is redirected to %windir%\lastgood\SysWOW64. Access to %windir%\regedit.exe is redirected to %windir%\SysWOW64\regedit.exe.

If the access causes the system to display the UAC prompt, redirection does not occur. Instead, the 64-bit version of the requested file is launched. To prevent this problem, either specify the SysWOW64 directory to avoid redirection and ensure access to the 32-bit version of the file, or run the 32-bit application with administrator privileges so the UAC prompt is not displayed. 继续阅读