Enabling MySQL Slow Query Logs

In the case your seeing very long pageload times, and have checked your application. It always pays to check the way in which the database performs when interacting with the application, especially if they are on either same or seperate server, as these significantly affect the way that your application will run.


mysql> SET GLOBAL slow_query_log = 'ON' ;
Query OK, 0 rows affected (0.01 sec)

mysql> SET GLOBAL slow_query_log_file = '/slow_query_logs/slow_query_logs.txt';
Query OK, 0 rows affected (0.00 sec)

mysql> SET GLOBAL long_query_time = 5;
Query OK, 0 rows affected (0.00 sec)

Migrating a Plesk site after moving keeps going to default plesk page

So today a customer had this really weird issue where we could see that the website domain that had been moved from one server to a new plesk server, wasn’t correctly loading. It actually turned out to be simple, and when trying to access a file on the domain like I would get the phpinfo.php file.

curl http://www.customerswebsite.com/info.php 

This suggested to me the website documentroot was working, and the only thing missing was probably the index. This is what it actually did turn out to me.

I wanted to test though that info.php really was in this documentroot, and not some other virtualhost documentroot, so I moved the info.php file to randomnumbers12313.php and the page still loaded, this confirms by adding that file on the filesystem that all is well, and that I found correct site, important when troubleshooting vast configurations.

I also found a really handy one liner for troubleshooting which file it comes out, this might not be great on a really busy server, but you could still grep for your IP address as well.

Visit the broken/affected website we will troubleshoot

curl -I somecustomerswebsite.com

Give all visitors to all apache websites occurring now whilst we visit it ourselves for testing

tail -f /var/log/httpd/*.log 

This will show us which virtualhost and/or path is being accessed, from where.

Give only visitors to all apache websites occurring on a given IP

tail -f /var/log/httpd/*.log  | grep 4.2.2.4

Where 4.2.2.4 is your IP address your using to visit the site. If you don’t know what your Ip is type icanhazip into google, or ‘what is my ip’, job done.

Fixing the Plesk website without a directory index

[root@mehcakes-App1 conf]# plesk bin domain --update somecustomerswebsite.com -nginx-serve-php true -apache-directory-index index.php

Simple enough… but could be a pain if you don’t know what your looking for.

Site keeps on going down because of spiders

So a Rackspace customer was consistently having an issue with their site going down, even after the number of workers were increased. It looked like in this customers case they were being hit really hard by yahoo slurp, google bot, a href bot, and many many others.

So I checked the hour the customer was affected, and found that over that hour just yahoo slurp and google bot accounted for 415 of the requests. This made up like 25% of all the requests to the site so it was certainly a possibility the max workers were being reached due to spikes in traffic from bots, in parallel with potential spikes in usual visitors.

[root@www logs]#  grep '01/Mar/2017:10:' access_log | egrep -i 'www.google.com/bot.html|http://help.yahoo.com/help/us/ysearch/slurp' |  wc -l
415

It wasn’t a complete theory, but was the best with all the available information I had, since everything else had been checked. The only thing that remains is the number of retransmits for that machine. All in all it was a victory, and this was so awesome, I’m now thinking of making a tool that will do this in more automated way.

I don’t know if this is the best way to find google bot and yahoo bot spiders, but it seems like a good method to start.

Count number of IP’s over a given time period in Apache Log

So, a customer had an outage, and wasn’t sure what caused it. It looked like some IP’s were hammering the site, so I wrote this quite one liner just to sort the IP’s numerically, so that uniq -c can count the duplicate requests, this way we can count exactly how many times a given IP makes a request in any given minute or hour:

Any given minute

# grep '24/Feb/2017:10:03' /var/www/html/website.com/access.log | awk '{print $1}' | sort -k2nr | uniq -c

Any given hour

# grep '24/Feb/2017:10:' /var/www/html/website.com/access.log | awk '{print $1}' | sort -k2nr | uniq -c

Any Given day

# grep '24/Feb/2017:' /var/www/html/website.com/access.log | awk '{print $1}' | sort -k2nr | uniq -c

Any Given Month

# grep '/Feb/2017:' /var/www/html/website.com/access.log | awk '{print $1}' | sort -k2nr | uniq -c

Any Given Year

# grep '/2017:' /var/www/html/website.com/access.log | awk '{print $1}' | sort -k2nr | uniq -c

Any given year might cause dupes though, and I’m sure there is a better way of doing that which is more specific

Comparing Files on the internet or CDN with MD5 to determine if they present same content

So, a customer today was having some issues with their CDN. They said that their SSL CDN was presenting a different image, than the HTTP CDN. So, I thought the best way to begin any troubleshooting process would firstly be to try and recreate those issues. To do that, I need a way to compare the files programmatically, enter md5sum a handly little shell application usually installed by default on most Linux OS.

[user@cbast3 ~]$ curl https://3485asd3jjc839c9d3-08e84cacaacfcebda9281e3a9724b749.ssl.cf3.rackcdn.com/companies/5825cb13f2e6c9632807d103/header.jpeg -o file ; cat file | md5sum
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  382k  100  382k    0     0  1726k      0 --:--:-- --:--:-- --:--:-- 1732k
e917a67bbe34d4eb2d4fe5a87ce90de0  -
[user@cbast3 ~]$ curl http://3485asd3jjc839c9d3-08e84cacaacfcebda9281e3a9724b749.r45.cf3.rackcdn.com/companies/5825cb13f2e6c9632807d103/header.jpeg -o file2 ; cat file2 | md5sum
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100  382k  100  382k    0     0  2071k      0 --:--:-- --:--:-- --:--:-- 2081k
e917a67bbe34d4eb2d4fe5a87ce90de0  -

As we can see from the output of both, the md5sum (the hashing) of the two files is the same, this means there is a statistically very very very high chance the content is exactly the same, especially when passing several hundred characters or more. The hashing algorithm is combination based, so the more characters, the less likely same combination is of coming around twice!

In this case I was able to disprove the customers claim’s. Not because I wanted to, but because I wanted to solve their issue. These results show me, the issue must be, if it is with the CDN, with a local edgenode local to the customer having the issue. Since I am unable to recreate it from my location, it is therefore not unreasonable to assume that it is a client side issue, or a failure on our CDN edgenode side, local to the customer. That’s how I troubleshooted this, and quite happy with this one! Took about 2 minutes to do, and a few minutes to come up with. A quick and useful check indeed, which reduces the number of possibilities considerably in tracing down the issue!

Cheers &
Best wishes,
Adam

Please note the real CDN location has been altered for privacy reasons

Aaron Mehar’s CBS to VHD solution for Rackspace Cloud

Hey. So another one of my colleagues put together this really awesome article. Although I was aware this could be done, he’s done a really good job or putting together the procedures, of turning your CBS BFV (boot from (network) volume) disk into a VHD file.

Rackspace CBS disks works over iscsi and are presented via the network. The difference between instance store on the hypervisor, (utilized by cloud-server images), and the disk store on the CBS is that the CBS disk is not a VHD, but an disk presented over network via iscsi.

So, to take a VHD, or an equivalent cloud-server image snapshot, you need to image the disk manually, as well as convert it to VHD.

Taking an image of a volume is not possible, and would not be downloadable. However there are some workarounds that can be done.

*** Please NOTE ****
This is not supported, and we can not assist beyond these instructions. I could provide some clarity if required, however, my collegaues may not be able to help should I become unavailable.

If you just want the data, then you could just download the data to your local machine, however, if you a VHD to create a local VM, then the below instructions will achieve this.

Steps

Please take special care, making a mistake working with partitioner can wipe all your data

1. Shutdown the server
2. Clone the disk, by Starting a volume clone and start the server back up.
3. Attach the newly created clone to the server
4. create another new CBS volume of a slightly larger size (+5GB is OK)

Now that is done, we can image the disk. You will need to ensure you have the corrects disks. The second disk with data should be xvbd and the new CBS should be xvdc

Create partition and filesystem for xvdbc. Please see this guide: https://support.rackspace.com/how-to/prepare-your-cloud-block-storage-volume/

the image xvdb to xvdc

   dd if=/dev/xvdb of=/mnt/cbsvolume1/myimage.dd

The download the image to your workstation, and install VirtualBox, and run the below command

   VBoxManage convertfromraw myfile.dd myfile.vhd --format VHD

Please take special care, making a mistake working with partitioner can wipe all your data

Help! I can’t login to my cloud-server even though I’ve reset my root password

The most common cause of this is the permit root login is set to no, although there might be other causes, like a really broken sshd_config, instead of just one variable. The procedure for looking into this is pretty much the same regardless of the breakage that has occurred. Here is what you need to do:

Here’s the full procedure:

1) Put server into rescue mode.
2) Login to cloud-server on SSH port, please note rescue mode gives you a new temporary root password allowing you to reset the password for SSH on the ‘original disk’.
3) once logged in mount the /dev/xvdb devices, this may be /dev/xvdb1 or /dev/xvdb2 but is usually /dev/xvdb1 and chroot (change root to the ‘original disk’)

# Mount old disk
mnt /dev/xvdb1 /mnt

# Change to the ‘old disk’
chroot /mnt

# Set the new password for root on the old disk:

passwd
# enter the new password when prompted

and specifically ensure that /etc/ssh/sshd_config has this line:

PermitRootLogin no

changed to:

PermitRootLogin yes

Your developer or sysad won’t be able to login until you reset the root password here, and if you do not know the username to su to root from, it is absolutely critical to perform this work, otherwise you won’t be able to access the server.

Also, once you have allowed the root login, and changed the password to something you recognise you will be able to exit rescue mode thru the control panel and login to the machine as normal.

For more detail about how to do this (although all the steps are here pretty much, please see):

https://support.rackspace.com/how-to/rackspace-cloud-essentials-rescue-mode-on-linux-cloud-servers/

I hope this helps you folks out some,

DISASTER RECOVERY! Exporting a Broken Cloud-server image VHD from Rackspace and attempting to recover data

Thanks to my colleague Marcin for thie guestmount tools protip.

I wrote a previous guide which explains how to download/export a Cloud server image VHD from Rackspace Cloud, which is failing to build. It might allow you to perform data recovery, even if the image can’t be booted. Which I’m guessing someone is going to run into sooner or later, and will be pleased to see this article, it will at least give you a best shot at reading the VHD and recovering it, since as you might know already, just because boot or kernel is broken, doesn’t mean that the data isn’t there!

# A better article to use if you want to download via commandline
https://community.rackspace.com/products/f/25/t/3583

# My article doing this thru a web-browser which might be useful too for some customers
https://community.rackspace.com/products/f/25/t/7089

Once the image gets downloaded to your new cloud instance you can use ‘libguestfs-tools’ package (same name on Ubuntu and CentOS) which contains tools necessary for mounting .vhd image files.

The command would be (read-only mode):

guestmount -a {image-name}.vhd -i --ro {mount-point}

Securing your WordPress with chmod 644 and chmod 755 the easy (but pro) way

Let’s say we have a document root like:

It’s interesting to note the instructions for this will vary from environment to environment, it depends on which user is looking after apache2, etc.

/var/www/mysite.com/htdocs

Make all files read/write and owned by www-data apache2 user only

root@meine:/var/www/mysite.com/htdocs# find . -type f -exec chown apache2:apache2 {} \; 
root@meine:/var/www/mysite.com/htdocs# find . -type f -exec chmod 644 {} \;

Make all folders accessible Read + Execute, but no write permissions

root@meine:/var/www/mysite.com/htdocs# find . -type d -exec chmod 755 {} \;
root@meine:/var/www/mysite.com/htdocs# find . -type d -exec chown apache2:apache2 {} \;

PLEASE NOTE THIS BREAKS YOUR WORDPRESS ABILITY TO AUTO-UPDATE ITSELF. BUT IT IS MORE SECURE 😀

Note debian users, may need to use www-data:www-data instead.

Automating Backups in Public Cloud using Cloud Files

Hey folks, I know it’s been a little while since I put an article together. However I have been putting together a really article explaining how to write bespoke backup systems for the Rackspace Community. It’s a proof of concept/demonstration/tutorial as opposed to a production application. However people looking to create custom cloud backup scripts may benefit from the experience of reading thru it.

You can see the article at the below URL:

https://community.rackspace.com/products/f/25/t/7857