We were targeted earlier today by a DDoS attack. There was 20x as many connections as normal on our load balancer (HAProxy), and all the backend nodes continued to go down during this attack.  System structure: HAProxy &gt; Squid &gt; Apache (for ModSecurity) &gt; IIS app layer.   During the attack, I noticed that there was a MaxClients Reached error in Apache, so I bumped the setting from 150 to 250, and it seemed to help to some extent. However, it seemed that I had to keep restarting Apache manually in order for the backends to recover. The attack lasted for about 50 minutes.  After the attack began to subside, a final Apache restart on each node brought us into the green, but now I'm looking into why it occurred in the first place. In the error logs in Apache, I see a lot of these:  [Wed Jun 22 11:46:12 2011] [error] [client 10.x.x.x] proxy: Error reading from remote server returned by /favicon.ico [Wed Jun 22 11:46:13 2011] [error] [client 10.x.x.x] (70007)The timeout specified has expired: proxy: error reading status line from remote server www.example.com   Apache is using default keep-alive settings (keep-alives are enabled and timeout is set to 15 seconds). After doing some additional reading on HAProxy + keep-alives, is it a reasonable conclusion to believe that the DDoS was worsened by keep-alives being enabled?  While the HAProxy max connections are way below the maximums set in Apache, perhaps with the 20x connections too many connections were being opened in the ol' DOS fashion, but then Apache was keeping them open.
This is a  about DoS and DDoS mitigation.   I found a massive traffic spike on a website that I host today; I am getting thousands of connections a second and I see I'm using all 100Mbps of my available bandwidth.  Nobody can access my site because all the requests time out, and I can't even log into the server because SSH times out too!  This has happened a couple times before, and each time it's lasted a couple hours and gone away on its own.  Occasionally, my website has another distinct but related problem: my server's load average (which is usually around .25) rockets up to 20 or more and nobody can access my site just the same as the other case.  It also goes away after a few hours.  Restarting my server doesn't help; what can I do to make my site accessible again, and what is happening?  Relatedly, I found once that for a day or two, every time I started my service, it got a connection from a particular IP address and then crashed.  As soon as I started it up again, this happened again and it crashed again.  How is that similar, and what can I do about it?
I have the bike, I have the best route; but now I want to know, how do I transport my clothing in each day? I typically wear suit pants and a business shirt, but not a suit jacket.   Am I better off leaving my clothes at work, or is there a special bag that would let me carry in shirt/pants without them getting crushed? $a\equiv\bar a\!\pmod{\!kn}\Rightarrow a\equiv\bar a\!\pmod{\! n};\ $ $(a\bmod kn)\bmod n=a\bmod n.\ $ Congruences persist mod factors of the modulus I noticed relation between modulo operation and number which is power of two  Example I have to calculate $ 3431242341 \mod 2^5 $, which is $ 5 $ but it is equivalent to  $ ( 3431242341 \mod 2^9 ) \mod 2^5 $   I tried many examples and it seems to be true in general, and I am not sure if it is a coincidence or true in general that I can use first modulo operation ( greater number) and the result will be the same. How did the Community user earn the Civic Duty badge? Apparently, .  How the heck did that happen? Is there a way to load every label data and every SObject description data using only Javascript without any Apex Server-side code?  How do I import * from @salesforce/schema or @salesforce/label?  I am looking for a way to get all labels or all SObject describe information details to retrieve in LWC at once.  I can see that such syntax is provided by ES6 and is used widely by Salesforce itself, however, it is not possible to use the following syntax in LWC:   import * as schema from '@salesforce/schema'   import * as label from '@salesforce/label'   or this syntax  import {label, schema} from '@salesforce';   since both versions generate error     LWC1512: Missing resource value for @salesforce"   or      LWC1512: Missing resource value for @salesforce/label   Is there a way to load every label data and every SObject description data using only Javascript without any Apex Server-side code?  By the way, if we look as Salesforce Playground we could notice that   the same syntax is used to import everything from lwc  import * as Engine from 'lwc';   however, if we try to insert such line into any of Lightning Web Component, we would receive the following error     LWC1001: Invalid import. Namespace imports are not allowed on "lwc",   instead use named imports "import { LightningElement } from 'lwc'"   or   LWC1517: Invalid LWC import FastBoot recovery failed: partition 'recovery' not support flash How to Select Columns in Editors (Atom,Notepad++, Kate, VIM, Sublime, Textpad,etc) and IDEs (NetBeans, IntelliJ IDEA, Eclipse, Visual Studio, etc) I get the following error when i do sudo apt-get update  W: GPG error: http://ppa.launchpad.net precise Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 6AF0E940624A220   I tried following ways after reading various questions here and also by googling.  I tried  sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 6AF0E1940624A220   It did not help. I also tried  sudo gpg --keyserver hkp://keyserver.ubuntu.com:80 --recv-keys   thinking port 11371(default) may be blocked due to firewall.  I also tried to reset everything as follows  sudo rm /var/lib/apt/lists/* -vf sudo apt-get update &amp;&amp; sudo apt-get upgrade   still i get the same error or get update. Any other possible solution I can try? How can I encourage Stack Overflow to rein in the 'subjective' vigilantes? Why should I put a ~ before \ref or \cite? My question is in the title of this post, but extends to other referencing commands like \eqref, \citep, \citet (and the like) as well. FireFox 66 Quantum disabled all my extensions at midnight! This morning I woke up to:    and the FireFox help page doesn't really help...  Help!  What should I do now??? I need NoScript and AdBlock Plus to improve my surfing speed!!! 0:-) Find all positive integers $a, b, c$ such that $1/a + 1/b + 1/c = 4/3999$ Find all positive integers $a, b, c$ such that $1/a + 1/b + 1/c = 4/3999$.  The contest is just ended, so you may freely answer. (I did not attend the contest: it is an Italian contest for schools and the groups may ask other people for hints. This is how I got involved, but of course asking on MSE would have been cheating)  I found three solutions: I am explaining below what I did. I would like however to know if there is a more general approach. How can this English sentence be translated into a logical expression? ( Translating " unless") You cannot ride the roller coaster if you are under 4 feet tall unless you are older than 16 years old.   Let:   $P$ stands for "you can ride the roller coaster" $Q$ stands for "you are under 4 feet tall" $R$ stands for "you are older than 16 years old"   Is this logical expression correctly translated?  $$P \rightarrow (Q \wedge R)$$ script custom previews in a menu I want to know how to create a menu with previews for an add-on. Until now I know that this is related with the bpy.utils.preview. I'm making an add-on that appends objects from a .blend file, I know how to append objects but what I want to do is to create a menu with previews of the objects /(similar to the matcaps menu - see below), select them and then press an &quot;import button&quot; to append the object. Here's some documentation about the module:    Also, as this is an add-on I don't know if I should have a def register() and a def unregister() inside this .py file as well as in the __init__.py file. How do I fix my USB drive to get its original 8GB size back? My USB drive used to be originally 8GB when I bought it.  I'm trying to reformatted in Windows 7 by right clicking on the drive and selecting Format.... But the capacity only shows 250MB.  Is there something I can do to get the original size back? Maybe it got partitioned in a weird way?   The  flash drive is a SanDisk Cruzer Micro 8GB. I got it from Wal-Mart but this is the same drive. No notification (+15) for accepted answer Yesterday my answer was accepted, but I got no notification in top bar, moreover, top bar still shows that I earned 45 reps  while reputation tab shows right 60 rep.  Update: July, 11 Again having this problem: In the dropdown:  In the rep tab:  You see, first down votes in the drop down are missing. In 1735 Euler gave the value of $\gamma$ as $0.577218.$ The constant is generally defined as the limit of the difference between the harmonic series and $\log n:~\gamma= \lim_{n\to\infty}\sum_{k=1}^{n}\frac{1}{k}-\log n.$ Euler apparently relished this sort of calculation and must have taken quite a few terms to get such a good approximation.  My question is whether without a computer one can now prove that  $$\gamma &lt;  \sqrt{1/3}$$   with at least some savings in terms of the type of work Euler apparently expended? I don't think there's any point in raising the bar to $\gamma &lt; \ln 2\sqrt{\frac{23}{29}} $  because it seems to be the same sort of question.       My own thought was to compare $\frac{1}{2}\int_0^{1/3}\frac{dx}{\sqrt{x}}$ to something like $(-1)\cdot\int_0^\infty e^{-u}\ln u~du$ but I expect there's a better way. Deriving the Coulomb force equation from the idea of photon exchange? Then what is the probability that out of $n$ men $A_1,A_2,....,A_n$ each aged $x$ years,$A_1$ will die and will be the first to die Let $p$ be the probability that a man aged $x$ years will die in a year time.Then what is the probability that out of $n$ men $A_1,A_2,....,A_n$ each aged $x$ years,$A_1$ will die and will be the first to die?  The probability that a man aged $x$ years will die in a year time$=p$  The probability that a man aged $x$ years will not die in a year time$=1-p$  But from here on,i got stuck.Some hints and suggestions are welcome. Here are some tips for tagging questions. These guidelines will help you more accurately tag your questions, which in turn will help them get more attention and lead to better answers faster.     For more information, see "" in the . Is there a way to kill a process tree using the terminal?  By killing a process tree, I mean killing all descendants of a process along with the process it self.  I tagged this question htop because I am using that utility a lot these days and it would be cool if there was an easy way to kill a process tree inside htop (something better than just selecting all the processes in the subtree).