Tag Archives: vps

 

Lesson Learned: Backup Before Upgrading

Friday started with off quite crazy with a surprise from my web hosting server. I don’t really know why but I decided to run an apt-get upgrade last night and everything seemed fine until this morning when I was unable to log back on via SSH. So what did I do? Reboot, obviously and it broke everything. Ping was lost, services are down, websites not working, oh my!

I know my web hosting provider wouldn’t help much since I’m renting a virtual private server with root access which comes with a lot of responsibility, besides I was quite sure I’d handle it faster than I would have opened a support request and described the details, and I did!

Luckily I was able to use the Change OS feature and grabbed Ubuntu 11.04 which was installed within 20 minutes with all my old files in the /old directory. The rest was up to my typing speed — install necessary software, copy the old MySQL databases, restore the users, set up nginx and php-fpm and voila. I was back online. Approximate downtime: 45 minutes.

Lesson learned: backup your full VPS container before upgrading. Thank you Media Temple for providing the freedom to break things and the tools to fix them :)

Published 7 months ago with 2 comments tagged , , ,


 

Linux Dummy: Unscheduled Maintenance

If anyone of you have tried to access the blog yesterday night, you might have noticed that nothing was working. Sorry! I’ll say it straight, it’s completely my fault. Yesterday evening I decided to set up a cron job for automatic backups on my VPS – a full MySQL dump and a compressed archive of the www directory. So I got a couple of error messages stating that I don’t have the right to access some files which were in the wp-content/upload and wp-content/cache folders… I was frustrated!

Next… Never attempt to do this, okay? I logged in as root, changed owner on all files and folders including sub-folders of the www directory, set it to kovshenin:kovshenin. Voila, the backup worked! In a couple of minutes my VPS ran out of memory and I couldn’t even logon via SSH to reboot the server!

Now that’s funny! I called my hosting provider this morning and asked them what happened? They said everything’s fine, rebooted my server. I managed to logon by SSH, ran the “top” command, and looked at my memory usage growth! 100% was reached in 17 minutes, and bang! Disconnect. Two more calls to my provider didn’t help. They said that the only thing they can do is reset my yesterday’s VPS state completely.

So what really happened? I’m not sure but I bet it’s the WP-Super Cache plugin for WordPress! You see, cached files were created by the user that the httpd (apache) daemon ran – thus, one called “webmaster”. The user “kovshenin” apperantly didn’t have access to those files, and the change owner command spoiled all the cache! Now the static files were owned by “kovshenin”, and “webmaster” (apache) didn’t have any rights for those files. WP-Super Cache must have been in an infinite loop trying to access those, and of course, with no luck – therefore memory leak.

After another reboot I managed to quickly get into the WordPress control panel, enable Maintenance Mode and disable all the other plugins. Enabled them one by one. Setting 0777 as the rights for the cache directory and two WP-Super Cache config files solved the problem. The site was working fine again, and the new generated cache files were owned by “webmaster”… The day has been saved.

But what about the backups? Finally, I came to a thought that both “kovshenin” and “webmaster” users should be in the same groups. So I added “webmaster” to the “kovshenin” group, and “kovshenin” to the “webmaster”. Everything’s great! Apart from the fact that my Google Analytics now shows 0 visitors for 21.05.2009. Jeez, what a dummy…

Published 3 years ago with 3 comments tagged , , , , , , ,


 

Benchmarking: Your Web Hosting is Not That Perfect

Today I realized that the VPS I’m renting for $20/mo is not as good as it seemed at first. Ever thought about high loads? Okay, this may sound like some DDoS hacking tools, but no! 100 requests with 10 simultaneous made my virtual private server think for ~ 1,5 minutes. Jeez!

It took me quite some time to find good software for running some load tests on my webserver, linux has some good utilities (linux.com/feature/143896), but I suggest you start from ApacheBench which is a command line utility bundled with the Apache distribution. It’s cross-platform, therefore you can use it on Windows (I did). Anyways, here’s how you launch a test:

ab -n 100 -c 10 http://www.microsoft.com/

Why did I pick Microsoft? Well, if I get like 10,000 views tomorrow and everybody tries that command, that’d be a DDoS attack on Microsoft servers and I think they’re good enough to handle it. My server would just explode :)

Anyways, take a look at what the results may be like:

Benchmarking www.kovshenin.com (be patient).....done

Server Software:        Apache/2.2.8
Server Hostname:        www.kovshenin.com
Server Port:            80

Document Path:          /
Document Length:        84 bytes

Concurrency Level:      10
Time taken for tests:   90.984 seconds
Complete requests:      100
Failed requests:        1
   (Connect: 0, Receive: 0, Length: 1, Exceptions: 0)
Write errors:           0
Non-2xx responses:      100
Total transferred:      36564 bytes
HTML transferred:       8674 bytes
Requests per second:    1.10 [#/sec] (mean)
Time per request:       9098.438 [ms] (mean)
Time per request:       909.844 [ms] (mean, across all concurrent requests)
Transfer rate:          0.39 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0   15   3.4     16      16
Processing:  2203 8866 8879.2   6188   48797
Waiting:     1969 8532 8664.9   5891   48750
Total:       2219 8880 8879.6   6203   48813

Percentage of the requests served within a certain time (ms)
  50%   6203
  66%   7281
  75%   8141
  80%   8313
  90%  17078
  95%  32266
  98%  43813
  99%  48813
 100%  48813 (longest request)

Ah.. And a failed request there, how sad… You might also want to check out your load on the server while benchmarking. Use the ‘top’ command, it should produce similar output:

Yup, although the super cache plugin is working, wordpress consumes a lot of memory… I also ran this with a 500/100 requests, that made my server go down for like 6 minutes, I had over 200 failed requests and my blog kept saying database connection error until the test had finished. Free memory dropped down to 0! Scary? For more information about how ab works, read Apache HTTP server benchmarking tool documentation at apache.org.

Published 4 years ago with no comments tagged , , , , , , , ,



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